Editing Catherine Halsey

{{Status|Canon}}{{Status|Featured}}
{{Character infobox
|variant=Human
|name=Catherine Halsey
|image=[[File:H5G - Halsey.jpg|350px]]
|homeworld=[[Endymion]]<ref name="WaypointCatherineHalsey">[https://www.halowaypoint.com/en-us/universe/characters/catherine-elizabeth-halsey '''Halo Waypoint''' - ''Catherine Halsey'']</ref>
|birth=[[2492#March|March 19, 2492]]{{Ref/Reuse|WaypointCatherineHalsey}}
|death=
|causeofdeath=
|parents=
|siblings=
|spouses=
|children=[[Miranda Keyes]] {{C|daughter}}
|species=[[Human]]{{Ref/Reuse|WaypointCatherineHalsey}}
|gender=Female{{Ref/Reuse|WaypointCatherineHalsey}}
|height={{Convert|170.2|cm|ftin|sp=us}}<ref name="H4TEVG14">''[[Halo 4: The Essential Visual Guide]]'', ''page 14''</ref>
|mass=*{{Convert|56.7|kg|lb}} {{C|pre-amputation}}<ref name="HTEVG">'''[[Halo: The Essential Visual Guide]]''', ''page 90''</ref>
*{{Convert|117|lb|kg|disp=flip}} {{C|post-amputation}}{{Ref/Reuse|WaypointCatherineHalsey}}
|hair=*Gray{{Ref/Reuse|WaypointCatherineHalsey}}
*Black {{C|formerly}}<ref name="HTFORTAS">''[[Halo: The Fall of Reach - The Animated Series]]''</ref>{{Ref/Reuse|HSS22}}
|eyes=Blue{{Ref/Reuse|WaypointCatherineHalsey}}
|affiliation=[[Office of Naval Intelligence]]{{Ref/Reuse|WaypointCatherineHalsey}} {{C|formerly}}
|rank-title=Doctorate|rank=MD, PhD
|sn=*CC-409871{{Ref/Reuse|WaypointCatherineHalsey}}
*CIN-10141-026-SRB4695{{Ref/Reuse|HTFOR6}}
|notable=[[Artificial limb|Prosthetic arm]]
}}
{{Quote|For a long time I had thought that we had to sacrifice a few for the good of the entire human race. I have killed and maimed and caused a great deal of suffering to many people—all in the name of self-preservation. But now I'm not sure that philosophy has worked out too well. I should have been trying to save every single human life—no matter what it cost.|Catherine Halsey to [[John-117]] regarding her changed views.}}<ref name="HFS27">''[[Halo: First Strike]]'', ''Chapter 27''</ref>

'''Doctor Catherine Elizabeth Halsey''', (Civilian Consultant 409871, phonetically identified as "'''Charlie Hotel'''"),<ref>[[Halo Graphic Novel, Page 122|'''Halo Graphic Novel''', ''page 122'']]</ref> is a key scientific adviser of the [[Office of Naval Intelligence]], best known for her work with the [[SPARTAN-II program]], developing and creating [[smart AI]]s such as [[Cortana]], and for overseeing the development of the [[MJOLNIR Powered Assault Armor]]. She served as a scientific adviser for ONI from [[2515]] to [[2522]], when she was made chief scientist,<ref name="alph">'''[[Halo 3: ODST]]''', map ''[[Alpha Site]]'' - [[ONI Memorial]]</ref> a position she held until the end of the [[Human-Covenant War]].<ref>'''Halo: Glasslands''', ''page 286''</ref>

Halsey held considerable authority within ONI, despite being a [[civilian]], and commanded respect from important military figures.<ref name="fs123">'''Halo: First Strike''', ''page 123''</ref> Though generally well-regarded among her peers, she endured intense personal guilt for condemning the Spartans to the life of a super soldier. After the Covenant War, Dr. Halsey was stripped of her position, incarcerated, and treated as a [[war criminal]] by the UNSC at large, which led to her apparent defection to [[Jul 'Mdama]]'s [[Jul 'Mdama's Covenant|reformed Covenant]].<ref>'''Spartan Ops''', episodes ''[[Catherine]]'' through ''[[Exodus (Spartan Ops)|Exodus]]''</ref> After almost a year among the enemy, she was recaptured by the UNSC and commissioned to work on urgent scientific matters, particularly concerning the rise of the [[Guardian]]s.<ref>'''Halo 5: Guardians'''</ref>

==Biography==
===Early life and education===
{{Quote|The Office of Naval Intelligence had apparently had their eye on me for years and knew that the only way to convince me to join them was to get ''me'' to convince me. It worked. I joined.|Catherine Halsey recalls her recruitment by ONI in [[Dr. Halsey's personal journal|her journal]].}}{{Ref/Reuse|HJ12410}}
[[File:Halsey self portrait.jpg|thumb|300px|This self-portrait was sketched by Halsey at the age of eighteen, just a few months after she began her work on Reach.{{Ref/Reuse|HJ8810}}]]
Catherine Elizabeth Halsey was born on [[2492#March|March 19, 2492]] within the colony of [[Endymion]]'s coastal city of [[Port Vernon]].{{Ref/Reuse|WaypointCatherineHalsey}} While an impressionable young child, her father recited to her every adventurous tale of [[Wikipedia:L. Frank Baum|L. Frank Baum]]'s [[Wikipedia:Land of Oz|Oz]].<ref name="HJ9447">''[[Dr. Halsey's personal journal]]'', ''September 4, 2547''</ref> At this age, she was already contemplating ideas having to do with [[artificial intelligence]]s and their longevity.{{Ref/Reuse|HJ9447}} As an adolescent, she was already smarter than her parents and was continually reading, learning, and talking, being eager to share her knowledge with anyone who would listen.<ref name="HTFOR25">''[[Halo: The Fall of Reach]]'', ''Chapter 25''</ref> Among the works Halsey read was an [[English]] translation of [[Wikipedia:Dante Alighieri|Dante]]'s ''[[Wikipedia:Inferno (Dante)|Inferno]]''.{{Ref/Reuse|HG18}} The first game of [[chess]] Catherine that played with her mother was the only one she ever lost to her.<ref name="HJ11749">''[[Dr. Halsey's personal journal]]'', ''November 7, 2549''</ref> Upon beating her daughter she had said, in [[Human languages|Italian]], "When the game is over, the king and pawn go into the same box."{{Ref/Reuse|HJ11749}} At a young age, Halsey was sent to the elite academy [[Endymion Gifted]], where she continued to defy educatory standards. She was eventually afforded a trip to [[Circumstance]] in [[2501]] from the Dean of Biological Science at [[Koletre-Browning University]], who completely funded her education until the completion of her second doctoral thesis sometime after her fifteenth birthday in [[2507]].{{Ref/Reuse|WaypointCatherineHalsey}} While working on that second thesis, Halsey learned various [[Wikipedia:Command-line interface|line command]]s, long discarded and forgotten due to their archaic nature, with which she could interact with computer programs.<ref name="HFS13">''[[Halo: First Strike]]'', ''Chapter 13''</ref> 

In 2507, while still a doctoral candidate, Halsey met Doctor [[Elias Carver]] at an academic social mixer and couldn't resist correcting his obsolete algorithm implementation when she heard him describing the matrix mechanics of the socio-economic and politico-economic vectors of human expansion.<ref name="HJ12410">''[[Dr. Halsey's personal journal]]'', ''December 4, 2510''</ref> She outlined a corrective matrix calculation to him which revised his dimensional parameters so that the sixteen dimensions were used rather than seven. Doctor Carver did not appreciate being challenged by someone he saw as a young upstart, but her words seemingly caused [[Captain]] [[Michael Stanforth]] of the [[United Nations Space Command]]'s [[Office of Naval Intelligence]] to take note of her. Three weeks later, a [[Wikipedia:Grant (money)|grant]] she had proposed for using [[artificial intelligence]]s to control N-dimensional matrices was green-lit by the UNSC, with its funding contingent on the successful testing of a model of its choosing. Naturally, it was Carver's model which she was directed to test. Halsey knew his flawed model would produce flawed results, so she ran her sixteen dimensional variant as a [[Wikipedia:Controlling for a variable|control]] in addition to his seven-dimensional version. Carver's model predicted a breakdown of social order in the [[Outer Colonies]] within twenty years unless strict governmental control was established, reinforced by an immediate and permanent military presence. Catherine ran more than fourteen hundred simulations during this time, varying every parameter, and even in the best-case scenario it was clear to her that the Outer Colonies at large would [[Insurrection|rebel]] against the [[Unified Earth Government]] ''soon''. She determined that at a minimum, the resulting conflict would lead to thirty years of war and the deaths of five billion people. The maximum effect was unbounded and could involve interminable war and a new [[Wikipedia:Dark Ages (historiography)|Dark Age]] for [[humanity]]. Halsey took her findings to Stanforth only to learn that ONI had already reached the same conclusion. The agency had been keeping an eye on her for years and it had been decided that in order to recruit her, she would need to convince herself that working with the agency was necessary to save the human race.{{Ref/Reuse|HJ12410}} [[Ysionris Jeromi]], who considered Halsey his star pupil at the time, discouraged her from working with ONI.<ref name="HTFOR6">''[[Halo: The Fall of Reach]]'', ''Chapter 6''</ref> Halsey, however, had no problem admitting that ONI's tactic had worked on her.{{Ref/Reuse|HJ12410}} She allowed herself to be recruited in [[2508]] and in early [[2510]] she was brought to the [[Inner Colony]] of [[Reach]] and contracted to work as a [[civilian]] consultant on a number of classified projects.{{Ref/Reuse|WaypointCatherineHalsey}}<ref name="HJ8810">''[[Dr. Halsey's personal journal]]'', ''August 8, 2510''</ref><ref name="HM60">''[[Halo Mythos]]'', ''page 60''</ref>

===Spartan origins===
{{Quote|There is an ancient saying, "The beginning of wisdom is ignorance." So where do we begin to create the ultimate warrior? With innocence.|Halsey, writing in her journal, appropriates a maxim oft attributed to [[Wikipedia:Socrates|Socrates]] for her own ends.}}{{Ref/Reuse|HJ61913}}
After arriving at Reach, Doctor Halsey spent a few months setting up the new laboratory afforded to her.{{Ref/Reuse|HJ8810}} For weeks prior to [[2510#August|August 8, 2510]] she found it impossible to concentrate due to the confluence of new [[Insurrectionist|insurgent]] reports, new ideas, and the constant supervision of ONI. At one point during this time she stopped at a local shop while coming from the main base where she was stationed and purchased a cup of [[coffee]] and a [[Dr. Halsey's personal journal|journal]] in which she could record her thoughts and research notes without having to fear them being read by anyone in ONI. By August 8, the day on which she recorded her first entry in this journal, she had begun to undertake [[Spartan-II Program|a project]] she had been simultaneously dreading, desiring, and being inspired by. By this point Catherine had already designed a number of intrusion algorithms that could be employed to bypass [[artificial intelligence]]-enhanced data recording and storage systems.{{Ref/Reuse|HJ8810}} By [[2510#December|December 4]] of that year Halsey's new lab was still unstaffed apart from herself and racks of [[A.I.]] matrices and optical routers which were yet to be removed from their sealed crates.{{Ref/Reuse|HJ12410}} While sitting in the lab on this date Halsey endeavored to create her second entry in her journal, recalling the series of events which had led her to Reach and to be working for ONI. She ended the entry by asking how many lives would need to be spent to save all humanity and whether any price was too high to pay in order to ensure its security, resuming her work thereafter. Evidently to aid in this endeavor, she also made herself a reminder to acquire more dark [[coffee]].{{Ref/Reuse|HJ12410}} On [[2511#February|February 15, 2511]], Doctor Halsey in her journal went over details of the [[ORION Project]] and recorded ways in which she believed [[Spartan-II Program|its successor]] could improve on what it had accomplished.<ref name="HJ21511">''[[Dr. Halsey's personal journal]]'', ''February 15, 2511''</ref>[[File:HM-Halsey.png|250px|thumb|left|At just twenty-two or twenty-three years old, Halsey became the youngest scientific advisor in ONI's history in 2515.{{Ref/Reuse|WaypointCatherineHalsey}}]] ORION had been designed to create a nontraditional force of soldiers in order to remove the budding dissident leadership in the Outer Colonies without massive carnage, and to this end volunteers were recruited from the UNSC's [[UNSC Special Forces|Special Forces]]. Based on the failures documented surrounding the genetic augmentation and immunosuppressant administration provided to ORION candidates, Halsey determined that the most suitable candidates for a future generation of augmented warriors would need to be prepubescent and possess more malleable and robust [[Wikipedia:DNA|DNA]] structures and [[Wikipedia:DNA polymerase|repair enzymes]]. In order to locate individuals with the improbable genetic criteria required, she calculated that thirty-nine billion DNA records would need to be screened. Halsey realized the [[Colonial Administration Authority]]'s [[Outer Colony vaccination program]] possessed the largest DNA database at that time and resolved to recalibrate her selection criteria to find markers which would expedite the sifting process. Additionally, she recognized that in order to mitigate the [[Wikipedia:Posttraumatic stress disorder|posttraumatic stress disorder]] and sympathy for the insurgents exhibited by many from ORION, total indoctrination would be required. She was opposed to the sort of brainwashing several of her counterparts in the intelligence community had suggested, noting instead that the mission of "[[Spartan-II Program|Generation-II ORION]]" demanded at least a decade of training, persuasion and acclimation. Above all, she wrote, absolute control must be maintained over those chosen. It was clear to Halsey, based on these parameters, that children were ideal for this project. The ethical and moral implications of such an idea forced her to take extra time to think about this, however. Illustrations drawn in her journal on this date outlined her considerations of various [[human augmentation]]s suitable for the next generation of the ORION Project, which she also was considering renaming something more inspirational on behalf of her military counterparts.{{Ref/Reuse|HJ21511}} Just over a week later, on [[2511#February|February 23]], Halsey read the news about a [[Nuclear weapon|nuclear]] [[terrorism|terror attack]] at the [[Haven arcology]] on [[Mamore]] which left two million dead and millions more expected to die from the fallout.<ref name="HJ22311">''[[Dr. Halsey's personal journal]]'', ''February 23, 2511''</ref> It was reported that the [[Freedom and Liberation Party]] was claiming responsibility and upon learning this Halsey became even more convinced than she already had been that she ''had'' to stop the violence in the Outer Colonies from escalating further.{{Ref/Reuse|HJ22311}}

On [[2511#July|July 30, 2511]] Halsey received test results for a new [[polymerized lithium niobocene]].<ref name="HJ73011">''[[Dr. Halsey's personal journal]]'', ''July 30, 2511''</ref> The material had been developed for discharging the vast amount of static energy that plagued ships in [[Slipspace|slipstream space]] but Halsey was interested in its potential applications as a sheath or suit of artificial muscle for a Gen-II ORION soldier. Though manufacturing an entire suit with it was cost-prohibitive at that point, Halsey mentioned in her journal on this date that Stanforth, now a vice admiral and the head of [[ONI#Section Three|ONI Section Three]], had assured her this would be addressed in the "production phase" of the project.{{Ref/Reuse|HJ73011}}{{Ref/Reuse|HTFOR1}} Given the scope, Halsey remained doubtful.{{Ref/Reuse|HJ73011}} Additionally, although she believed there was a way to couple the polymerized lithium niobocene to a wearer's nerve inductions to increase reaction time and had created notes on the subject and stored them within the A.I. [[Jorjet]], she had yet to solve the matter of the energy required for such a design. She'd concluded a small nuclear or fusion reactor would need to be attached to the suit, which would be unwieldy, dangerous, and expensive.{{Ref/Reuse|HJ73011}} Halsey and others agreed that the concept behind the Navy's original [[MJOLNIR Powered Assault Armor#Mark I exoskeleton|Mark I prototype]] [[powered exoskeleton]]s needed to be scrapped for [[Mjolnir|Project: MJOLNIR]].{{Ref/Reuse|HJ73011}}{{Ref/Reuse|HTFOR8}} Needing to be plugged into a generator or to rely on [[Wikipedia:Wireless power transfer|broadcast power]] made them wholly inefficient for battlefield use.{{Ref/Reuse|HTFOR8}} Looking over the Mark I's antiquated design at this time, Halsey still wondered how much of it could remain useful.{{Ref/Reuse|HJ73011}}

On [[2511#September|September 8, 2511]] Halsey recorded in her journal that she had recently finalized the control parameters for a [[Wikipedia:Fast Fourier transform|Fast Fourier transform]] X-ray [[Wikipedia:3D|3D]] scan for mapping a brain's ionic density patterns that indicate individual links.<ref name="HJ9811">''[[Dr. Halsey's personal journal]]'', ''September 8, 2511''</ref> This meant that a deep stimulating scan could then cultivate growth linkages in a cloned brain, thereby allowing [[Mind transfer|memories to be transferred]] for the first time. Complete human clones could feasibly now be produced that were indistinguishable from the individual they were based on. The potential application of this breakthrough for ORION-II was obvious, and Halsey was of the mind that stealing children away and replacing them with clones would mean there would be no going back. By the time she updated her journal with this, she had already informed the vice admiral that they were ready to initiate the next phase of the project: candidate procurement. She had done this knowing that only a small fraction of the clones they produced could be expected to live a normal lifespan due to the amount of DNA base-pair errors rapid [[flash cloning]] of large volumes of tissue produced. Beyond what this breakthrough meant for her current project, Halsey also speculated on whether this technique could imprint the next-generation of [[artificial intelligence]]s and in so doing avoid the [[Wikipedia:Wave function|wavefunction]] collapse that had plagued the functionality of previous generations.{{Ref/Reuse|HJ9811}}

On [[2513#June|June 19, 2513]], Doctor Halsey settled on a new name for the project.<ref name="HJ61913">''[[Dr. Halsey's personal journal]]'', ''June 19, 2513''</ref><ref name="H61913">[[343 Industries|Halo]] on Twitter 06/19/2513 [https://twitter.com/Halo/status/215143433965273088]</ref> Stanforth had seemed to hint that rechristening the project would serve to distance it from the failures of ORION.{{Ref/Reuse|HJ61913}} After having [[Jorjet]] and [[Déjà]] (an A.I. created to assist her with the program) give her a refresher on military history which produced a number of contenders, she decided "SPARTAN" best represented the project's aims.{{Ref/Reuse|HJ61913}}{{Ref/Novel|Id=HSS20|HSS|Chapter=20}} The [[Wikipedia:Sparta|Spartans]] of [[Wikipedia:Ancient Greece|Ancient Greece]] had been known for their legendary training of young boys and eugenic customs, and the [[Wikipedia:Battle of Thermopylae|defense of Greece]] made at [[Wikipedia:Thermopylae|Thermopylae]] was a well-known and cherished tale within the military community.{{Ref/Reuse|HJ61913}} Coincidentally, Halsey did not fail to note, her project had originally been funded for three hundred candidates. In order to honor the sacrifices made by the men and women of the original ORION effort, she opted to call the project "[[Spartan-II Program|SPARTAN-II]]", preserving its status as the second iteration of that first effort.{{Ref/Reuse|HJ61913}} In [[2515]], Halsey was officially named a scientific advisor for ONI.{{Ref/Reuse|WaypointCatherineHalsey}}

===Candidate selection===
{{Quote|no=three|q1=We screen these subjects for certain genetic markers. Strength, agility, even predispositions for aggression and intellect. But we couldn’t remote test for everything. We don’t test for luck.|Catherine Halsey|q2=Luck? You believe in luck, Doctor?|Jacob Keyes|q3=Of course not. But we have one hundred and fifty test subjects to consider, and facilities and funding for only half that number. It’s a simple mathematical elimination, Lieutenant. That child was one of the lucky ones—either that or he is extraordinarily fast. Either way, he’s in.|Catherine Halsey|Doctor Halsey defends her peculiar means of testing [[John-117|John]].}}<ref name="HTFOR2">''[[Halo: The Fall of Reach]]'', ''Chapter 2''</ref>
[[File:FORAS HalseyKeyesHan.png|350px|thumb|It only took one brief encounter between Halsey and Keyes as they both came out of cryostasis for her to crystallize their roles and the rules of conduct, making him understand she was in charge despite being a [[civilian]].{{Ref/Reuse|HTFOR1}}]]
By [[2517#July|July 21, 2517]], Halsey had been provided with her own team, to which she delegated much of the responsibly for screening Outer Colonies candidates for SPARTAN-II.<ref name="HJ72117">''[[Dr. Halsey's personal journal]]'', ''July 21, 2517''</ref> She did this so it might be completed within a reasonable time frame and so that she could personally focus on processing those from a single region of space: [[FLEETCOM Sector Four|Sector 4]].{{Ref/Reuse|HJ72117}} The children from this [[sector]] which met the criteria Halsey had identified in her original study had files assembled personally by her.{{Ref/Reuse|HTFOR2}} In total, one hundred and fifty subjects were to be considered. The Spartan-II program, of which Halsey was the chief scientist and administrative overseer, had only been granted facilities and funding for half that number, however, so only seventy-five would ultimately be selected.{{Ref/Reuse|HTFOR2}}{{Ref/Reuse|HO4}} And even then, an ONI representative reminded Halsey that not all would make it through the [[Project ASTER|augmentation procedures]] when the time came for that.{{Ref/Reuse|HTFOR3}} Vice Admiral Stanforth had agreed to lend Halsey a {{Class|Vancouver|courier}} called the ''Han'', provided that she agreed to at least one naval officer accompanying her.{{Ref/Reuse|HTFOR1}} Halsey was given free reign to choose her attaché and after reading through the file of one [[Lieutenant (disambiguation)|Lieutenant Junior Grade]] [[Jacob Keyes]], she requested him based on his demonstrated ability to keep a secret. Keyes was then, without any explanation provided to him as to why, assigned to pilot the ''Han'', protect the doctor, and otherwise stay out of her way.<ref name="HTFOR1">''[[Halo: The Fall of Reach]]'', ''Chapter 1''</ref>{{Ref/Reuse|HJ72117}} On July 21 Halsey wrote in her journal that she was considering recommending him for permanent reassignment to her staff.{{Ref/Reuse|HJ72117}} The ''Han'' also came with its own dedicated artificial intelligence by the name of [[Toran]].{{Ref/Reuse|HJ72117}}

Halsey was awakened from [[cryostasis]] alongside Keyes shortly after 0430 hours on [[2517#August|August 17]] while the ''[[Han]]'' was still in slipspace but set to emerge soon in the [[Eridanus system]].{{Ref/Reuse|HTFOR1}} Giving not so much as an acknowledgement that they were both naked, Halsey simply climbed out of her tube and told the lieutenant to get cleaned up and dressed as she headed for the showers herself, making it clear to Keyes that she was in charge. Halsey was already strapped into the navigator's couch and on the bridge and tapping in commands across four keypads when he joined her soon thereafter. The doctor welcomed him and asked that he be seated at the communication station to monitor channels when they reentered normal space. She then had [[Toran]] provide her with [[astronavigation]] maps of the system and asked if any planets between their current position and [[Eridanus II]] could be used to pick up a [[Wikipedia:Gravity assist|gravitational boost]] to let them arrive sooner. Additionally, in rapid succession she had the A.I. begin to play [[Rachmaninov's Piano Concerto Number Three]], begin a preburn warmup cycle for their [[fusion engine]]s, and halt the rotation of the shuttle's central carousel section to conserve power. Toran obliged with each request and informed her that they would be exiting slipspace in about five minutes, give or take three minutes. From the way Keyes was glancing at her, Halsey could tell he was impressed at her ability to put Toran through his paces so rigorously, so she asked if he had a question for her. In response he composed himself before inquiring as to the exactly what they were doing. Halsey told him that they were on a reconnaissance mission of sorts, as they were heading to Eridanus II in order to observe [[John-117|a child]] whom she hoped would only be the first of many. She suggested the junior lieutenant should just think of it as a UNSC-funded psychological study and then sternly told him that was exactly what he was to say it was to anyone who asked. The ''Han'' soon decelerated as it dropped out of slipspace near a gas giant and then began a hard burn, accelerating for sixty-seven seconds before arcing away from the planet. As soon as the boost was complete Toran informed the two humans that their [[Wikipedia:Estimated time of arrival|ETA]] was forty-three minutes and three seconds. At this, Halsey unlocked her harness and floated free. Just before they had dropped into normal space, Keyes had started to ask her if she knew how dangerous the Eridanus system was then and now she finally answered him in the affirmative. After stretching and strapping herself back into her couch, she reminded her escort that he was supposed to be monitoring their comms for that very reason. Catherine spent the next thirty minutes with her back to Keyes while she read over reports on her navigation screens. The Keyes eventually spoke up to candidly ask why he was there, and Halsey told him the truth about why she had selected him for the job. She also assured him that though he may have rather been on the {{UNSCShip|Magellan}} then, which now-rescinded orders had previously had him rotating to, the child they were traveling to observe could make all the difference for the ongoing struggle against the [[Insurrection]]. Once Toran announced they were approaching Eridanus II Halsey had him plot an atmospheric vector for the [[Luxor]] [[Luxor Spaceport|spaceport]] and ordered Keyes to make ready to land.{{Ref/Reuse|HTFOR1}}
[[File:FORTAS Halseyplayground.png|thumb|350px|left|For a moment after meeting John, Halsey envied the boy's innocence.{{Ref/Reuse|HTFOR2}} Her own, after all, was already long dead.{{Ref/Reuse|HTFOR2}}]]
Halsey and Keyes made their way onto the campus of [[Elysium City]]'s [[Elysium City Primary Education Facility Number 119|Primary Education Facility Number 119]] under the guise of parents inspecting the school for their little girl.{{Ref/Reuse|HTFOR2}} By 1130 hours they were watching children at play from the semi-shade of a canvas awning. Halsey, wearing a sundress and straw hat, urged the lieutenant to appear more relaxed and even tried to help by slipping her arm through his, but her efforts were in vain. It was Keyes, however, who first identified their subject, a six-year-old boy named [[John-117|John]], after Halsey showed an image to him. John was atop a grassy hill at the end of the school's playground, engaged in a particularly vicious game of [[king of the hill]]. Halsey's first instinct was to point her [[data pad]] at the boy to record the incident for later study. After glancing around to see that the only other adult present was marching an injured girl toward the nurse's office Halsey ordered Keyes to stay back and keep watch while she walked over to get a closer look at their boy. She stopped at four meters from the base of the hill and asked to speak with John, whom the other boys assumed must be in trouble. She led him to the edge of a nearby sandpit and asked his name, which he freely offered before holding out his hand to be shook. She asked what he was had been doing and John answered that he had been winning. Seeing that the boy was fond of games, she produced a [[quarter]] and told him that if he could guess which side of the coin would be facing upwards when it landed after being flipped, he could keep it. She let it go but before it could hit the ground John snatched it out of the air and confidently declared "Eagle!" referring to the side of the quarter which was, indeed, facing up when he opened his hand. Assured he could keep the coin for himself, he asked if they could play again but Halsey told him that had been the only one she had. She told him he ought to go back to his friends and returned to the lieutenant, asking to make sure he had recorded the interaction. He had, and after reviewing the footage Halsey sent it to Toran on the ''Han''. She explained to Keyes that the one thing they couldn't test their candidates for remotely was luck, further clarifying that she meant her test as a simple way to eliminate half of the qualified children due to the budgetary constraints of the program. She remarked that John whether John was lucky or just extraordinarily fast, he had made the cut. Keyes still did not fully understand her interest in the child and said as much, to which she replied that she hoped he never would fully understand their purpose there.{{Ref/Reuse|HTFOR2}}

After similar visits to multiple other children in Sector Four, The ''Han'' took them to [[Dwarka]], a harsh world still in the process of being [[Terraforming|terraformed]].<ref name="HEPP">''[[Halo: Evolutions]]'', ''[[Pariah]]'', ''Prologue''</ref> The child to be considered there was an orphan by the name of [[Soren-066|Soren]]. The report Halsey had previously read indicated the boy had survived on his own for around three months following the deaths of his mother and stepfather. Halsey left Keyes aboard the ''Han'' and approached Soren alone at the place he was being cared for by this point. She asked him his name, but admitted she already knew what it was and only wanted to see if he'd be willing to tell her. He had not been, evidently being deeply distrustful of the doctor. A pair of glasses Halsey wore allowed her to review [[holographic]] files on the lenses as she spoke to the boy, and as a result of his circumstances she chose to pursue a different strategy. She was as honest with him insofar as she told him she'd come to see him because she wanted to make him stronger, faster, and smarter than he could ever hope to be without her help. She also made sure he understood that if he chose to accept her offer, he would be faced with the hardest experiences he had yet―even harder than what had happened after his parents died. Faced with the choice of leaving with Doctor Halsey or being placed in a foster home, he quickly agreed to go with her. Halsey was able to convince the authorities that she was adopting the boy and bring him aboard the ''Han''. There she showed Keyes the footage she'd recorded of their conversation. The lieutenant was uneasy with her decision to take then child then. Halsey was sure that Soren would be a good fit, however, and defended his acquisition by pointing out at least he had been warned concerning what lay ahead.{{Ref/Reuse|HEPP}}

===SPARTAN-II===
[[File:Halseyrecruits.png|thumb|350px|Dr. Halsey looks over the profiles of the abducted children.]]
{{Main|SPARTAN-II program}}
Halsey and Keyes had returned to [[Reach]] by [[2517#September|September 10]] and it is on this date that Halsey told [[Déjà]] to let others know she had settled on the final seventy-five subjects.<ref name="HFORBC">''[[Halo: Fall of Reach]]'', ''[[Halo: Fall of Reach - Boot Camp|Boot Camp]]''</ref> Halsey was stationed in low Reach orbit when she gave final approval to kidnap the seventy-four which still remained to be acquired. Halsey later recorded a private spoken journal entry, using [[Encryption code|RED encryption]] and her private key, in which she voiced how regrettable she felt what she was doing was. She had planned to keep the recording private but changed her mind and just had Déjà erase it entirely once she had finished.{{Ref/Reuse|HFORBC}} On [[2517#September|September 15]] Halsey, writing in her journal, expressed that every child had exceeded the selection criteria and her own expectations.<ref name="HJ91517">''[[Dr. Halsey's personal journal]]'', ''September 15, 2517''</ref> She was particularly impressed by two: [[Linda-058|Number 058]], a girl named [[Linda-058|Linda]] who had engineered her own intelligence network at school to spy on her teachers, and John (Number 117), who had won king of the hill forty-five times in the two weeks before their meeting. Halsey noted that [[Caleb Aagard|Number 095]], a boy by the name of [[Caleb Aagard|Caleb]], had never been located. Later that day Halsey added an addendum to her journal entry after [[Retrieval team Gamma]] reported that [[Kelly-087|Number 087]], a girl named [[Kelly-087|Kelly]], had remarkably eluded capture for six hours before coming forward on her own, having believed her capture attempt to be an elaborate game for her upcoming birthday. Gamma's report caused Halsey to ensure new retrieval protocols were implemented to prevent similar mistakes in the future.{{Ref/Reuse|HJ91517}} The next day, [[2517#September|September 16]], Catherine and Jacob Keyes finally parted company after months together.{{Ref/Reuse|HJ91617}} Halsey felt he was beginning to suspect there was more to their incursions than mere field observations so she requested that he be reassigned to the ''Magellan'' with a commission to full lieutenant both for his own protection and the protection of the program. Taken with Keyes, she recalled in her journal on this date an occasion which he had gotten a job done himself rather than waiting for the assistance of a technical crew.<ref name="HTFOR3">''[[Halo: The Fall of Reach]]'', ''Chapter 3''</ref><ref name="HJ91617">''[[Dr. Halsey's personal journal]]'', ''September 16, 2517''</ref> Despite saying their goodbyes on the sixteenth, Halsey and Keyes briefly met once more the following day before parting for good.<ref name name="H91717">[[343 Industries|Halo]] on Twitter 09/17/2517 [https://twitter.com/Halo/status/247786318162186240]</ref> Once all the children had been collected Déjà undertook a psychological evaluation of each and provided the results and her recommendations to Doctor Halsey.{{Ref/Reuse|HTFOR3}} For years after this the doctor kept what she believed was the only set of records concerning the families who had lost children.<ref name="HG18">''[[Halo: Glasslands]]'', ''Chapter 18''</ref>
[[File:FORTAS HalseyAmphitheater.PNG|thumb|300px|left|Halsey briefs the trainees.]]
By 2300 hours on [[2517#September|September 23]] Halsey was standing on a platform at the center of an amphitheater within ONI's [[CASTLE Base]] (where her facilities were), itself located far beneath the planet's [[Reach FLEETCOM Military Complex|FLEETCOM military complex]].{{Ref/Reuse|HTFOR3}}<ref name="HMD12">''[[Halo: Mortal Dictata]]'', ''Chapter 12''</ref> When Déjà asked if she was ready to speak to the abducted children she told the A.I. she almost was but wished for her to summon [[Chief Petty Officer]] [[Franklin Mendez]], the [[drill instructor]] who would be overseeing the trainees' physical training and hand-to-hand combat, to join her first. She directed Mendez to join her on the platform once he entered. Déjà asked the doctor for her thoughts on the candidates' psychological evaluations and Halsey, while thanking her for their thoroughness, informed her she was forgoing her recommendation to lie to the children. Halsey argued that though the truth had its own risks, lying to the children about the circumstances of their kidnappings or even inducing memory loss could jeopardize the program's goals. Before Déjà could offer a response Halsey clicked her microphone and gave the command to bring the abductees in. Once all seventy-five were seated, she explained that per [[Naval Code 45812]], they were thereby conscripted into SPARTAN-II. She said that they were to be the [[UEG]]'s protectors and promised that here they would become the best they could be. She also informed them that they could not return to their homes or families. She closed by telling them to rest then, since their training would begin the next day. Halsey then instructed CPO Mendez to escort the trainees to their barracks to be fed and put to bed, also advising that they be kept plenty busy the following day in order to keep them from thinking about what had just been done to them.{{Ref/Reuse|HTFOR3}} Before all the children could file out of the amphitheater one boy asked Halsey if they were there to stop everyone from fighting and killing each other.{{Ref/Reuse|HTFOR3}}<ref name="HJ92317">''[[Dr. Halsey's personal journal]]'', ''September 23, 2517''</ref> Before the day was done Halsey noted in her journal that the first phase of the program's indoctrination was under way and that her team of ONI child psychologists was assuring her the children wouldn't even remember their names or families after just six months under Mendez' tutelage. Even so, she also wrote that she was working with Déjà to continue indoctrination protocols and the candidates' education.{{Ref/Reuse|HJ92317}} Before falling asleep Halsey nursed a glass of wine in bed while she viewed reporting on the [[Insurrection]].{{Ref/Reuse|HFORBC}} The news of an escalating death toll reinforced what she was doing to the children and she said as much to Déjà before having the A.I. show her footage of the children being fed.{{Ref/Reuse|HFORBC}} Over the course of the first three days Halsey met regularly to talk with the girl [[Naomi-010]] within CASTLE Base.{{Ref/Reuse|HMD12}} During one of these sessions, despite having originally intended to avoid lying to the children, Catherine told her that her father wouldn't be coming to rescue her because he knew she had an important job to do as a Spartan.{{Ref/Reuse|HMD12}} On the fifth day of training, the children were given haircuts.<ref name="HJ92817">''[[Dr. Halsey's personal journal]]'', ''September 28, 2517''</ref> Halsey took note in her journal that [[Kelly-087]] had clawed at and disarmed the master sergeant barber of his clippers before needing to be pinned down by three other attendants.{{Ref/Reuse|HJ92817}}

On [[2517#December|December 24]] Doctor Halsey received a batch of after-action reports regarding the fates of the clones used to replace most of the stolen children.<ref name="HJ122417">''[[Dr. Halsey's personal journal]]'', ''December 24, 2517''</ref> Overall, the clones' longevity had outpaced what laboratory experiments had predicted and Halsey wondered if this could have been owed to the efforts of parents to nurture them back to health. She assigned [[Codename: JACKBOOT|JACKBOOT]] to track this further. Writing in her journal, she expressed remorse for her inability to detach herself emotionally from the reports of suffering, death, and grieving.{{Ref/Reuse|HJ122417}} Seeing as the use of cloning for the Spartan program's purposes violated many legal statutes, Catherine made sure at some point that one of her A.I.s obfuscated her culpability in the budget.<ref name="HG14">''[[Halo: Glasslands]]'', ''Chapter 14''</ref> Halsey regularly observed the conscripted children from a distance and scribbled notes down during their exercises, with Soren sometimes noticing her watching him in particular.<ref name="HEP2">''[[Halo: Evolutions]]'', ''[[Pariah]]'', ''Chapter 2''</ref><ref name="HTCP8">''[[Halo: The Cole Protocol]]'', ''Chapter 8''</ref> By [[2518#December|December 10]] of [[2518]], she and CPO Mendez had identified [[Kurt-051]], [[Jerome-092]], [[Frederic-104]], and [[John-117]] as potential leaders for all the trainees. Though Chief Mendez wanted to wager on Kurt, she was confident John would be their leader eventually, something she had been convinced of since the day she'd met him. Halsey was also pleased that they had not yet witnessed the sort of aggressive alpha dominance predicted by ONI's specialists in any of the children.<ref name="HJD1018">''[[Dr. Halsey's personal journal]]'', ''December 10, 2518''</ref>

===Work continues===
[[File:SquadLeaderPromotion.png|thumb|350px|Halsey and Mendez meet with John.]]
{{Quote|I've instructed Déjà to emphasize the history of military training—that to simulate combat conditions, lethal force is often employed; that accidents are an inherent risk... perhaps even inevitable. Mendez spoke with [[Carris-137|the child]]. She understands. She will recover. This bodes well. There will be many deaths before boot is over.|Doctor Halsey considers the cost of the Spartan-II training and expresses optimism about the trainees' psychological hardiness.}}{{Ref/Reuse|HJS2020}}
One day, around five months into training, Doctor Halsey asked to see two children who had made repeated attempts to escape the program: [[Jai-006]] and [[Adriana-111]].{{Ref/Reuse|HTCP8}} When Chief Mendez brought Jai into her office she at first pretended he had been the one to initiate the visit before casually asking if he wanted to leave. The boy responded enthusiastically that he did, so she asked him to recall what she'd said to them all when they'd first arrived. Nodding regretfully at his clear recollection and persistent defiance, she then drew his attention to a small dart which she claimed could induce a selective neural paralysis and cause him to forget all of his experiences on Reach so far. She said that should he break out of the forest surrounding the complex again, he would be shot in the head with one of these darts and wake up in a city with no memory of what had happened, provided it didn't do further damage to him. On the other hand, she advised, he could continue his training under people who cared about what happened to him. To contrast his new life with his old, she told him that when [[State Dorm Five-Five|the orphanage]] on [[Bhuj]] he'd been housed in was called nobody there had even noticed he'd been missing since she had transferred him. Not even Bhuj's vendors, she'd claimed, remembered him. She finished by exploiting his blossoming friendship with Adriana and making him understand that she could also make her forget about him. Halsey told him that this was her final offer: if he tried to escape that night what she'd said about erasing memories would come to pass. If he stayed, conversely, she offered him a family and a chance to be remembered. Adriana's similar meeting with her left the girl in tears later that evening and unwilling to tell Jai what the doctor had said to her.{{Ref/Reuse|HTCP8}}

On [[2519#July|July 12, 2519]] the trainees were scattered throughout a [[Reach Military Wilderness Training Preserve|military wilderness training preserve]] in the [[Highland Mountains]] and left to find their own way to the extraction point, with the stipulation that the last to arrive would have to walk back to the base.<ref name="HTFOR5">''[[Halo: The Fall of Reach]]'', ''Chapter 5''</ref> John stubbornly refused to accept those parameters and led the children to steal the [[D96-TCE Albatross]] from the guards posted at the extraction point and, with help from [[Déjà]], fly them all back.{{Ref/Reuse|HTFOR5}} At around 2104 hours Halsey met John and Mendez in the latter's office, greeting the boy as she seated herself across from the Chief.{{Ref/Reuse|HTFORTAS}}{{Ref/Reuse|HFORBC}}{{Ref/Reuse|HTFOR5}} Once Mendez had finished questioning John regarding his actions, he looked to Halsey for advice regarding what ought to be done with him.{{Ref/Reuse|HTFOR5}} At this, she offered that it was obvious to her he should be made squad leader over the rest.{{Ref/Reuse|HTFOR5}} On [[2520#September|September 20, 2520]], the trainees experienced their first casualty in the form of a handler who was accidentally killed by [[Carris-137]].<ref name="HJS2020">''[[Dr. Halsey's personal journal]]'', ''September 20, 2520''</ref> Catherine saw Carris crying outside the barracks following this but decided to leave her alone. She and Chief Mendez both agreed that no disciplinary action was necessary. Memorial services were held with all candidates in attendance and training resumed thereafter. Halsey had Déjà emphasize to the children that throughout the history of military training lethal force had often been employed and that deaths were an inherent risk. Sure that Carris would recover after speaking with Mendez, Halsey chronicled her thoughts on the matter. She thought the girl's response boded well, since it seemed certain there would be many more deaths before boot camp was finished.{{Ref/Reuse|HJS2020}}  
[[File:Halsey MemoryCropped.PNG|thumb|300px|left|Halsey smiles at Keyes during their brief romance.]]
On [[2521#October|October 15, 2521]], while enjoying a slice of custard pie from [[Havadi Goodwan|Havadi]]'s, Halsey took the time to muse somewhat in her journal on the vulnerabilities created by the standardization of operating systems, highlighting the recent disabling of [[UNSC Persephone|a patrolling destroyer]] by a [[terrorist]] who hacked its code.<ref name="HJN1724">''[[Dr. Halsey's personal journal]]'', ''October 15, 2521''</ref> Given that the [[UNSC]], conversely, had not had much success penetrating the homegrown collections of software employed in the [[Outer Colonies]], she concluded that the time had come to think outside the box as far as programming practices were concerned. She had spared no resource in the development of routines that allowed the newly-operational third-generation A.I.s to penetrate any system software. Additionally, they had already learned to mutate and defend established UNSC operating systems from attack, a side effect of the routines which Halsey found serendipitous. Before she concluded writing that day, she took note of the frustration she felt at the way the acronyms for [[Illegal Entry Protocols|illegal entry protocols]] and [[Counter-Illegal Entry Protocols|counter-illegal entry protocols]] had been commonly misspelled and then vocalized based on those misspellings.{{Ref/Reuse|HJN1724}} On [[2522#June|June 5, 2522]] Halsey was finally offered the position of chief scientist within ONI, after years of only officially serving in an advisory role involving a series of undocumented but well-paid contracts.{{Ref/Reuse|HJN1724}}<ref name="JS6526">[[Jessica Shea]] on Twitter 06/05/2522 [https://twitter.com/bsangel/status/606903711663681536]</ref> Since she had always lacked the time or interest to spend the money earned, these contracts had always benefited her little. Halsey accepted the offer, but was uncertain why it had been presented to her then. In her journal she theorized that the promotion might have something do to with the curiosity of her colleagues and the wider scientific community or might simply reflect suspicions that her temporary unofficial advisory role was in reality none of those things.{{Ref/Reuse|HJN1724}} Once around this time, when [[Soren-066]] was nearly eleven years old, she approached him as he ran through an exercise with the other children.{{Ref/Reuse|HEP2}} Soren had been hesitating, unsure of which team to join, so she asked if everything was alright. The boy replied in the affirmative, but slipped up and called her "Sir" before blushing and correcting his mistake. Halsey just smiled and told him he shouldn't get distracted by irrelevant data, then pointed past him as both teams ran for the skirmish ground and added that above all he shouldn't let himself get left behind.{{Ref/Reuse|HEP2}} 

On [[2524#January|January 18, 2524]] [[Wikipedia:Canada–France–Hawaii Telescope|CFHT]]-[[Mars]] captured a ten-minute [[Wikipedia:Exposure (photography)|exposure]] image of an [[High Charity|anomalous object]] within the star cluster [[Wikipedia:NGC 2244|NGC 2244]] and nearing human space.{{Ref/Reuse|HJextras}}<ref name="H11824">[[343 Industries|Halo]] on Twitter 01/18/2524 [https://twitter.com/Halo/status/424662516803710976]</ref> [[J.C.|An acquaintance]] of Halsey's later sent her the image for evaluation along with a note describing the unidentified object as having guided movement and not belonging to the UNSC.{{Ref/Reuse|HJextras}}{{Ref/Reuse|H11824}} They also gave her a way to reach them on [[ChatterNet]], should she wish to weigh in on this mystery.{{Ref/Reuse|HJextras}} [[2524#August|August 22, 2524]] left Halsey furious after she learned that her candidates had been rerouted during a training exercise to a [[UNSC Special Forces|Special Forces]] camp on the other side of [[Reach]].{{Ref/Reuse|HJN1724}} Mendez had told her that "interested parties" within [[ONI]] wished to observe the teens in action firsthand, which made her immediately wonder about someone trying to usurp her project or cut its budget. She took her grievances to Admiral Stanforth, who claimed to know nothing about what had happened and told her to stop being paranoid. Convinced he was not being truthful and that something was going on without her knowledge, she requested that the production of the next-generation A.I. matrix strata be expedited so her new intrusion and counter-intrusion software could be developed to aid the Spartans and protect herself.{{Ref/Reuse|HJN1724}} On [[2524#November|November 17]] of that same year, Catherine made an entry in her journal following a conference she had attended at the [[University of Calippus]].{{Ref/Reuse|HJN1724}} While at the conference, she had reunited with [[Jacob Keyes]] and had sex with him.{{Ref/Reuse|WaypointCatherineHalsey}}{{Ref/Reuse|HJN1724}}<ref name="HG6">''[[Halo: Glasslands]]'', ''Chapter 6''</ref> She was unsure whether her decision to do so had been a result of the dizzying pressure she was under, a response to a chance encounter with a kindred spirit in a strange place, or something else, but she was glad it had been him she'd run into.{{Ref/Reuse|HJN1724}} The romantic liaison with Keyes left her pregnant with [[Miranda Keyes|a daughter]].{{Ref/Reuse|WaypointCatherineHalsey}}

===ASTER===
[[File:FORTAS HalseyAlert.PNG|thumb|350px|Dr. Halsey looking at a holographic display detailing which Spartans did not survive their augmentations.]]
{{Quote|no=four|q1=I have doubts, Déjà. I thought the reasons so compelling when we first started Project: SPARTAN. Now? I... I just don’t know.|Catherine Halsey|q2=I have been over the ONI projections of Outer Colony stability three times, Doctor. Their conclusion is correct: massive rebellion within twenty years unless drastic military action is taken. And you know the ‘drastic military action’ the brass would like. The Spartans are our only option to avoid overwhelming civilian losses. They will be the perfect pinpoint strike force. They can prevent a civil war.|Déjà|q3=Only if they survive to fulfill that mission. We should delay the procedures. More research needs to be done. We could use the time to work on [[MJOLNIR]]. We need time to—|Catherine Halsey|q4=There is another reason to proceed expeditiously. Although I am loath to bring this to your attention, I must. If the Office of Naval Intelligence detects a delay in their prize project, you will likely be replaced by someone who harbors... fewer doubts. And regrettably for the children, most likely someone less qualified.|Déjà|Halsey shares her concerns with Déjà.}}{{Ref/Reuse|HTFOR6}}
On [[2525#February|February 23, 2525]] Halsey got a chance to have a long chat with [[John-117|John]] during which, to her surprise, she learned he was convinced the Spartans were to enter a new, more severe phase of training.<ref name="HJF2325">''[[Dr. Halsey's personal journal]]'', ''February 23, 2525''</ref> Writing in her journal, she expressed her desire to share everything she could concerning the upcoming [[Project ASTER|augmentations]] and wondered if any of them would refuse were she to offer them the choice of whether or not to proceed. Déjà had continued to update and run Catherine's revision of [[Elias Carver]]'s model weekly by this point, and the results were only growing worse. This data made Halsey more resolute in her conviction that nobody involved had any choice but to forge the Spartans.{{Ref/Reuse|HJF2325}} Five days later, she gave birth to her daughter, [[Miranda Keyes|Miranda]].<ref name="WaypointMirandaKeyes">[https://www.halowaypoint.com/en-us/universe/characters/miranda-keyes '''Halo Waypoint''' - ''Miranda Keyes'']</ref> Near the end of February Halsey and the rest of her team sent their prototype suit of [[Mjolnir]] armor to [[UNSC Special Forces|Naval Special Weapons]] for evaluation.<ref name="HJ63025">''[[Dr. Halsey's personal journal]]'', ''June 30, 2525''</ref>

As the day for the Spartans' surgeries drew near, Catherine eventually summoned Soren to speak with her in her office.<ref name="HEP3">''[[Halo: Evolutions]]'', ''[[Pariah]]'', ''Chapter 3''</ref> The fourteen-year-old boy could tell that she was overworked and not getting enough sleep and even after she instructed him to sit she continued to scan through electronic files while whispering silently to herself. When she was finally ready to talk she asked Soren if he could remember the day they'd met on [[Dwarka]] and inquired as to his thoughts on the choice he'd made to join the Spartan program. He confirmed he was glad he chose the way he did, but Halsey shared that she had wondered whether it was right to lay such a burden on him at that age. Brushing the issue aside, she then let him know she'd asked for him then because she wished to give him another choice. She went on to explain the next step she had planned for he and the others: their physical augmentation. Halsey did not shy away from telling Soren the risks the necessary operations and therapies posed. When he asked why she had singled out him alone to give the choice of moving forward in this way to, she claimed that he was essentially to function as the [[Wikipedia:Control group|control group]] of the experiment but still could not say why he specifically had been chosen for this. After she had secured his consent the boy left and Halsey asked Déjà if she'd been listening and what her thoughts were on the matter. The A.I. pointed out that Halsey had misrepresented what a control group actually is and that she hadn't quite told him everything about the upcoming ordeal. In addition, she said she could tell that Halsey's purported justification for the reveal was spurious and it seemed to her more likely that the doctor was only trying to ease her conscience. Halsey could not disagree, dismissing Déjà to be alone with her thoughts.{{Ref/Reuse|HEP3}}

On March 9, the day before [[Project ASTER|Project: ASTER]] was to be initiated, Halsey and the seventy-five teens could be found aboard [[Medical Facility Endurance]] in orbit over Reach.<ref name="HTFOR6"/> At 1130 hours the doctor was pacing in the observation room while she waited for Déjà to decrypt [[UNSC Priority Transmission 09872H-98|a transmission]] from Vice Admiral [[Ysionris Jeromi]]. Catherine had previously proposed a hypothetical series of experiments involving [[Wikipedia:Bonobo|bonobo]]s to he and his team in order to obfuscate her true intentions for the protocols. To her dismay, the latest from Jeromi informed her that further analysis had failed to yield viable alternatives that might mitigate any of the risks inherent to her "hypothetical" experimentation. As soon as she was finished with the file he'd sent Halsey erased all traces of it and even sent Déjà to track its pathways all the way back to the {{UNSCShip|Hopeful}} to destroy his related notes and files. Given the news, Halsey seriously considered delaying the procedures and only put such thoughts aside due to Déjà pointing out that ONI would only find someone else to move the project forward if she started dragging her feet. Chief Mendez met the doctor in the hall outside the observation room and at her insistence followed her up the stairs to the hospital's pre-op wing. Upon seeing John in Room 117 she forced a smile and asked how he was feeling. John, thinking of the procedures as just another exercise, asked her if she could just this once tell him how to win. To that, she could only lean in close and tell him he needed to survive.{{Ref/Reuse|HTFOR6}} Later that day Halsey divided the various augmentations into two groups according to their risks of failure or long-term side effects not adequately studied.<ref name="HJ3925">''[[Dr. Halsey's personal journal]]'', ''March 9, 2525''</ref> Those that she considered to have unacceptable fail rates were to be tabled for then in order that further research could be done. Already she had begun to quietly arrange [[Operation: TENDRIL|long-term studies]] on the gradual application of cyclo-synthetic neural transmission gene sequences during subjects' early lives and noted in her journal that research on the injection of [[Wikipedia:Virus|viral]] [[Wikipedia:Neutrophil|microphage]]s at neuron surfaces was pending. Halsey closed that day's journal wishing there was a god to pray to.{{Ref/Reuse|HJ3925}} As she was being readied for the procedures within Lab 7, Halsey visited the girl [[Yasmine Zaman|Yasmine]] and assisted a nurse in strapping her down.<ref name="ILBPM">''[[i love bees]]'', [[Princess Monologue|princess monologue]]</ref><ref name="ILB12">''[[i love bees]]'', ''[[Axon Clips Chapter 12|Chapter 12]]''</ref> She attempted to reassure the girl that she would barely feel anything apart from slight pain that accompanies injections.{{Ref/Reuse|ILBPM}}{{Ref/Reuse|ILB12}}{{Ref/Note|In the [[Axon Clips Chapter 11|eleventh chapter]] of ''[[i love bees]]'' the A.I. [[Durga]] recites the date [[2537#September|September 16, 2537]] immediately after mentioning Yasmine's involuntary recruitment for the Spartan-II program. Following this recitation Durga mentions Yasmine's post-procedural designation as a medical washout. It may be likely that an error was introduced by seemingly having records which show her as having been abducted for the Spartan-II program years after Project: ASTER had been initiated. Whether the given date actually refers to her original childhood conscription, however, is not completely clear. She is also stated to have died prior to [[2546#January|January 2546]]. The possibility exists that each given date is in error due to having twenty years mistakenly added to the dates [[2517#September|September 17, 2517]] and [[2526#January|January 2526]].}} While visiting [[Serin-019]] before the procedures commenced the girl asked her how different she would feel when she woke up.{{Ref/Reuse|HG15}} Halsey was honest with her and let her know just how painful and persistent the side effects of the surgical enhancements would be if she survived—possibly lasting months or even years.{{Ref/Reuse|HG15}}

During the augmentation process [[Soren-066]] was returned to the Spartan compound on Reach, where he then woke during the procedures and violently attacked medical staff.<ref name="HEP4">''[[Halo: Evolutions]]'', ''[[Pariah]]'', ''Chapter 4''</ref> The young teen was stopped in a hall beyond the operating room he'd escaped from by CPO Mendez and a line of five or six marines. Out of breath from running, Catherine arrived on the scene just after Soren was hit numerous times with tranquilizer darts, pleading for him not to be hurt. Soren's last words before collapsing were used to ask Doctor Halsey what she had done to him.{{Ref/Reuse|HEP4}} When Project: ASTER's procedures were completed, only thirty-three of the teenagers had ostensibly been augmented successfully.{{Ref/Reuse|HTFOR6}} As far as these thirty-three were made aware, twelve others had been injured during the operations so severely that they would be unfit to be Spartans and the remaining thirty had died.{{Ref/Reuse|HTFOR6}} The truth, conversely, was that those pronounced dead were in fact cryogenically preserved in the hopes that they could be revived later, and some of those that were crippled would go on to be rehabilitated and join the ranks of [[Spartan-II]]s in the future.<ref name="HJ4125">''[[Dr. Halsey's personal journal]]'', ''April 1, 2525''</ref><ref name="HW2PLA130">''[[Halo Wars 2]]'', [[Phoenix Logs|phoenix logs]], [[Phoenix Logs#Alice-130|Alice-130]]</ref>

===Aftermath===
{{Quote|Was the need commensurate with the risk? We had to move quickly. The onset of puberty was the gating factor—that and the pressure from a growing insurgent threat. Must move forward. Find solutions. I'm sure the vice admiral's ONI trauma experts are reporting that I'm 'not letting go'. They can all go to hell.|Halsey relays her thoughts and feelings in her journal following the many failures produced by the augmentation processes.}}{{Ref/Reuse|HJ4125}}
By [[2525#March|March 30]] Halsey had joined the forty-five who had unambiguously survived aboard the {{UNSCShip|Atlas}}, an {{Class|Epoch|heavy carrier}} heading for the [[Lambda Serpentis system]].{{Ref/Reuse|HTFORTAS}}{{Ref/Reuse|HTFOR6}}<ref name="CF100">[https://www.halowaypoint.com/en-us/news/sweet-centennial '''Halo Waypoint''' - ''Canon Fodder #100: Sweet Centennial'']</ref> She had told John that some of the side effects he was experiencing which were causing him to be clumsy were actually good, since they were evidence of stronger muscles and faster reflexes.<ref name="HTFOR7">''[[Halo: The Fall of Reach]]'', ''Chapter 7''</ref> The next day she reflected in her journal on how her training as a scientist had conditioned her to view failure, struggling to reconcile the scientist's duty to regard all data as useful with the malformations and excruciating deaths visited on her Spartans.{{Ref/Reuse|HJ4125}} She allowed herself to question whether the need to push forward with ASTER had been commensurate with the threat the [[Insurrection]] posed. Halsey guessed that Stanforth's trauma experts would be reporting she was having difficulty "letting go", but she committed to moving forward and finding solutions for those who might still be saved. To this end the doctor had ordered that no candidate autopsies be performed. The bodies of washouts were cryogenically preserved, pending further study. Her hope was that some, if not all, of them could someday be revived. Closed casket funeral services at midnight the day before, she noted, would help the survivors attain psychological closure. She was uncertain how they might react in the future to the resurrection of their comrades but was certain ONI would find a use for them regardless. Those now afflicted by serious malformations, after all, had already been offered various "desk" duties within ONI. [[Serin-019]] was among those Halsey told the others had died, though in truth she had only been terribly crippled and would be delivered to [[Earth]] for ONI to take custody of her.{{Ref/Reuse|HG15}}<ref name="HG3">''[[Halo: Glasslands]]'', ''Chapter 3''</ref> Catherine had assigned Déjà to investigate as-yet theoretical therapies for the washouts' resuscitation. She was particularly interested in the potential of the complete restructuring of bones and attendant nanografts, something she thought could prove especially useful for [[Kirk-018]] and [[René-081]]. Even so, she decided she would allow the washouts to adjust to their new jobs for several months before suggesting some of these experimental procedures. By then, she figured, they would be willing to try anything to recover, as she couldn't imagine them to survive the vigorous indoctrination and training they had to only become passive spectators.{{Ref/Reuse|HJ4125}} [[File:FORTAS HalseyMendez.PNG|thumb|left|350px|Halsey and Mendez observe John remotely.]]The Atlas was patrolling the Lambda Serpentis system by April 22 and it was shortly after 0430 hours on this date that ONI engineered a hostile encounter between John and four [[ODST|orbital drop shock trooper]]s in order to test his capability.{{Ref/Reuse|HTFOR7}}<ref name="HTF5">''[[Halo: The Flood]]'', ''Chapter 5''</ref> Halsey observed the encounter in the ship's gym remotely, cooly remarking upon the boy's steady heart rate and pulse.{{Ref/Reuse|HTFORTAS}} John had broken the nose of one ODST when their sergeant intervened to propose that they settle their dispute in a nearby boxing ring.{{Ref/Reuse|HTFOR7}} Mendez, watching along with Halsey, questioned the wisdom of what was happening but his hesitation was rebuffed by her.{{Ref/Reuse|HTFORTAS}} She pointed out that John was only doing what they'd built him to do. As the chief left her to make his way to the gym she simply renewed her interest, wondering what effect the augmentations might have had on his adrenaline.{{Ref/Reuse|HTFORTAS}} Not long after the Spartans on the ''Atlas'' returned to Reach five of them elected to quit the program and escape.<ref name="HLH">''[[Halo Legends]]'', ''[[Homecoming]]''</ref>{{Ref/Reuse|HTTS19}} [[Daisy-023]], [[Ralph-103]], [[Joseph-122]], [[Oscar-129]], and one other boy managed to get ahold of [[M6C magnum]]s and hold at least seven individuals at gunpoint within a hallway, one of whom was Doctor Halsey. Daisy declared that they were leaving and could not be prevented from doing so. Daisy eventually was able to secure passage offworld and traveled to [[Sargasso]], where she had been born. Unbeknownst to her, she was followed by Halsey. Catherine caught up to the teenage girl outside her old home, having been flown there in an [[AV-14 Hornet]]. As Daisy was first laying eyes upon her own [[Flash cloning|clone]], Halsey chose to speak to her from the Hornet through a radio in her ear. She explained the rationale behind the production of the clones in [[2517]] and urged her to return home to Reach. In the end, Daisy, Ralph, and Joseph were brought back into the fold; Oscar and the other boy committed suicide.{{Ref/Reuse|HLH}}<ref name="HTTS19">''[[Hunt the Truth]]'', ''[[Hunt the Truth Season 1|Season 1]] Episode 09''</ref>

It was not until early June that Soren, counted among the washouts, awoke from a comatose state.<ref name="HEP5">''[[Halo: Evolutions]]'', ''[[Pariah]]'', ''Chapter 5''</ref> Repeatedly during the three months in which he was out it had been thought he would die and at one point the decision was even made to disconnect [[Wikipedia:Life support|life support]], but after four minutes of flatlining his heart had then begun to beat anew. Halsey paid him a visit in the brig where he was being held almost immediately after he woke up, flanked by an armed guard of two marines. She greeted the boy before looking him over and dismissing her guards, who were resistant at first but gave in when she claimed rank by virtue of being within a science facility. Halsey apologized for the restraints limiting Soren's movement and assured him she had argued against them but had been overruled. Following this she sat down on the floor within his reach and he joined her shortly thereafter. When Soren let her know he wasn't feeling quite right she said the analgesic [[Drugs|medications]] he was on were likely to blame and that others were dealing with varying degrees of pain just like he was. She explained that his body had reacted poorly to the administered muscular enhancement injections and [[Wikipedia:Thyroid|thyroid]] implant, ultimately resulting in intense musculoskeletal pain that she believed would diminish over time but likely never go away completely. She did note to him, however, that he had become stronger than anyone had imagined the Spartans could be. When Soren asked how many of his brothers and sisters remained, she told him almost half had died. At that she apologized before leaving without a further word a moment later.{{Ref/Reuse|HEP5}} By [[2525#June|June 27]] planning was underway for experimental surgery, therapies, and rehabilitations for more than eighty percent of the washouts.<ref name="HJ62725">''[[Dr. Halsey's personal journal]]'', ''June 27, 2525''</ref> Halsey noted in her journal that several of these protocols could take years to complete and that A.I.s were predicting a survival rate of no greater than fifty percent, but she also believed that her Spartans would exceed expectations just as they always had.{{Ref/Reuse|HJ62725}} The day which followed was the doctor's last official one at [[Camp Hathcock]].<ref name="HJ62825">''[[Dr. Halsey's personal journal]]'', ''June 28, 2525''</ref> [[UNSC Fleet Command|FLEETCOM]] had offered her a corner suite in the [[Olympic Tower]] in [[New Alexandria (location)|New Alexandria]], but she had turned it down in favor of [[CASTLE Base]], which was to serve as her new home from then on.{{Ref/Reuse|HJ62825}}<ref name="HRNA">''[[Halo: Reach]]'', ''[[New Alexandria]]''</ref> Her funding was shunted to higher profile projects and her access to classified materials was severely restricted around this time.{{Ref/Reuse|HTFOR25}} Each morning she became forced to pass through a dozen security checkpoints and submit to a barrage of retina, voice, fingerprint, and brainwave identification scans after descending into the base's labyrinth to reach her office.{{Ref/Reuse|HTFOR25}} On [[2525#June|June 30, 2525]] Halsey was shocked to learn Naval Special Weapons had approved limited-run production of Mjolnir.{{Ref/Reuse|HJ63025}} She had expected at least another three months to elapse before she got such news. She made a note to herself in her journal so she would be reminded to follow up with her source regarding [[First Battle of Harvest|what]] had prompted NAVSPECWEP's prompt decision. One file in the official response Catherine received also contained a partial routing code which she was able to backtrack through NAVSPECWEP's firewalls. Doing this revealed a volunteer had been put into the prototype suit against an emphatic warning she had made about the armor's reactive circuitry being fine-tuned for augmented Spartans. The man who had volunteered suffered the breaking of several bones and the snapping of his spine in three places. Halsey, in her journal, pledged that day she would find out who was responsible for ignoring the specific safety measures she'd put in place to prevent something like this and for failing to enable all the monitors.{{Ref/Reuse|HJ63025}}

===Time of testing===
[[File:TFORAS HalseyDeja.PNG|thumb|350px|Halsey and Déjà.]]
{{Quote|no=three|q1=Something has happened, Chief. Something ONI and the Admiralty never expected. The brass wants to deploy the Spartans. They want to test them in a real combat mission.|Catherine Halsey|q2=They’re as ready for that as I can make them. But this is far ahead of your schedule. What happened? I’ve heard rumors there was some heavy action near [[Harvest]] colony.|Franklin Mendez|q3=Your rumors are out-of-date, Chief. There’s no more fighting at Harvest. There ''is'' no more Harvest.|Catherine Halsey|Halsey breaks the horrifying news about Harvest to Chief Mendez.}}{{Ref/Reuse|HTFOR8}}
By [[2525#September|September 1, 2525]], Halsey had begun applying the new liquid metal crystal version of [[polymerized lithium niobocene]].<ref name="HJ9125">''[[Dr. Halsey's personal journal]]'', ''September 1, 2525''</ref> Its amorphous nature allowed it to be "poured" into a capillary system where microelectric fields could direct crystallization geometries. The material scaled fractally to double a Mjolnir wearer's strength, but Halsey believed she could exceed even this were she to ignore what she considered archaic safety regulations. In her journal she defended such a move by arguing that nobody had anticipated this technology when such regulations were put in place.{{Ref/Reuse|HJ9125}} Over the next ten days, Halsey spent some time on another trip that took her away from the [[Epsilon Eridani system]].{{Ref/Reuse|HTFOR8}} At one some point during this period [[Déjà]] brought to her attention a transmission from the planet [[Harvest]] in the [[Epsilon Indi system]] which the A.I. had been attempting to decode.{{Ref/Reuse|HTFORTAS}}{{Ref/Reuse|HTFOR8}} Halsey had Déjà show her what little she had and also asked for a feed from the planet, but nothing of the sort was accessible. The doctor urged her to keep trying.{{Ref/Reuse|HTFORTAS}} 

On [[2525#September|September 11]] Halsey had just returned to Reach.<ref name="HTFOR8">''[[Halo: The Fall of Reach]]'', ''Chapter 8''</ref> Chief Mendez was surprised to find her reclining in his chair when he opened the door to his office at 0930 hours that day, as he had been under the impression she would be gone for yet another week. She told him their situation had changed and asked to know where the Spartans were, since she had failed to locate them in their barracks or on any of the ranges. The Chief told her they'd been forced to find them other facilities recently and offered to show her what he meant. He then escorted her to his personal [[M12 Warthog]] and drove them both off of [[Reach FLEETCOM Military Complex|the base]] and onto winding mountain roads leading to a series of [[titanium]] mines. They passed a manned guardhouse before descending steeply underground through a tunnel which wound downward in a spiral. Mendez revealed that dozens of old [[MJOLNIR Powered Assault Armor#Mark I exoskeleton|Mark I]] exoskeletons had been stored down there and were now being used by the Spartans' trainers, three of whom had been accidentally killed on the first day back from [[Lambda Serpentis system|Lambda Serpentis]]. The vehicle came to a stop within a large cavern, Mendez helping her out and leading her to a small prefabricated one-room building. At the push of a button by Mendez the room climbed a track along the wall until they were twenty meters off the floor. When floodlights snapped on a game of [[Capture the Flag]] was illuminated in a large section of the cavern; trainers in armor defending against Spartans. Halsey could not see any of her Spartans at first, but she soon identified a glimpse of motion as Kelly. The trainers were armed with 30mm miniguns loaded with [[stun round]]s, but when one almost landed shots on John at point-plank range the doctor briefly panicked, for even stun rounds could kill at that distance.[[File:HTFOR Laden.PNG|left|thumb|350px|The five Spartans who infiltrated [[Eridanus Secundus]] to capture Colonel Watts did so by stowing away aboard the {{Class|Parabola|freighter}} ''[[Laden]]''.{{Ref/Reuse|HTFOR9}}]] Once the flag had been stolen without any sign of the Spartans remaining Halsey asked to see what she'd just witnessed again, sure that it had been recorded. Unfortunately, the teens had already found the cameras and disabled them. The Spartans' newfound impressive abilities made Catherine conclude there must be unexplained synergistic effects brought on by the combined modifications. Once she made sure to inquire about any physiological or mental instabilities, she then asked Mendez whether he thought they were ready to kill others in real combat. He believed they were, so she let him know [[First Battle of Harvest|something]] unexpected had happened and that [[UNSC High Command|the Admiralty]] wanted them deployed as a first test. Mendez rightly guessed that the rumors he'd heard about heavy action at Harvest had something to do with this, so it was left to Halsey to inform him that the colony there had been wiped out. She proceeded to bring the observation room back to the floor and told him she wanted the Spartans ready to muster at 0400 hours the next day for a briefing aboard the {{UNSCShip|Pioneer}}, a {{Class|Halberd|light destroyer}} which would take them on [[Operation: TALON|a mission]] ONI had been saving for the right crew at the right time. Tomorrow, she said, they would see if all the pain they'd put the Spartans through had been worth it.{{Ref/Reuse|HTFOR8}} At 0605 hours the next day both Halsey and Mendez met the Spartans in the ''Pioneer''{{'}}s briefing room while ''en route'' to the [[Eridanus system]].<ref name="HTFOR9">''[[Halo: The Fall of Reach]]'', ''Chapter 9''</ref> The doctor walked to a the podium and greeted them with good news: Command had decided to finally put their abilities to the test. The doctor explained that intelligence suggested an [[Eridanus Secundus|insurgent base]] had been established in the [[Eridanus system]]'s [[Asteroid|asteroid belt]] by rebel elements who had escaped [[Operation: TREBUCHET]] years before. She further introduced them to the [[United Rebel Front|URF]] leader [[Robert Watts]] and announced that they were to infiltrate the base to capture him alive to be returned to UNSC-controlled space. Halsey then stepped aside so Chief Mendez could go over the details of [[Operation: TALON|the operation]]. When finished, he and Halsey left the room.{{Ref/Reuse|HTFOR9}}

===Meeting the enemy===
{{Quote|no=five|q1=May I suggest that we go to battle stations, Captain?|Catherine Halsey|q2=I don't see the point.|Wallace|q3=We haven't let this be widely known, but when the aliens were first detected at Harvest, they appeared at extreme range... and then they were suddenly much closer.|Catherine Halsey|q4=An intrasystem jump?|John-117|q5=Correctly surmised, Spartan.|Catherine Halsey.|Doctor Halsey makes sure the ''Commonwealth''{{'}}s captain knows the threat posed by the Covenant in [[space warfare|naval engagements]].}}{{Ref/Reuse|HTFOR12}}
At some point following October 7, Doctor Halsey officially requested access to [[ONI Colonial Security Estimate 2525.10.110|the data archive]] of an [[RQ-XII Drone|RQ-XII drone]] originally deployed from the {{UNSCShip|Walk of Shame}} and recovered by the {{CMAShip|Heracles}} at [[Harvest]].{{Ref/Reuse|HCHE}} Her request was granted with a warning that all queries would be logged in accordance with [[Office of Naval Intelligence Protocol A1|protocol]]. Halsey searched the archive using the keywords "AO.AI", "Mack" "rampancy" and "lifespan limits". The data captured in the log was formed of messages from the agricultural operations A.I. [[Mack]] intended for [[Sif]], the planet's shipping operations A.I. The garbled messages demonstrated the A.I.'s descent into rampancy over a period of eight months.<ref name="HCHE">''[[Halo: Contact Harvest]]'', ''Epilogue''</ref> The ''Pioneer'' did not return to [[Reach]] until [[2525#November|November 2 of 2525]].{{Ref/Reuse|HTFORTAS}} At 0600 hours that day Halsey met the Spartans within the same secure briefing amphitheater where she'd introduced herself to them years earlier.<ref name="HTFOR11">''[[Halo: The Fall of Reach]]'', ''Chapter 11''</ref> They were also joined by Chief Mendez and Admiral [[Michael Stanforth|Stanforth]], who informed the teenagers that [[Harvest]] had been [[First Battle of Harvest|annihilated]] some time ago by what appeared to be alien attackers. The adversary responsible called itself "the Covenant" and had broadcast a message announcing that the destruction of [[humanity]] was the will of its [[Forerunner|god]]s. Stanforth told them that the UNSC had been ordered to full alert and that the largest fleet action in human history was being mobilized in response. And because of the UNSC-wide mobilization, the Spartans' training was to be accelerated to its final phase: [[Mjolnir|Project: MJOLNIR]]. Halsey spoke briefly with Mendez and Stanforth following the meeting's conclusion before leaving with the admiral.{{Ref/Reuse|HTFOR11}} At some point soon after the revelation of their new alien enemies, the doctor and others made sure to add a refractive coating to the design of the shell for each set of armor in order to disperse energy weapon attacks.<ref name="HTFOR13">''[[Halo: The Fall of Reach]]'', ''Chapter 13''</ref> By [[2525#November|November 6]], Halsey and the Spartans had departed [[Reach]] aboard the {{Class|Paris|heavy frigate}} {{UNSCShip|Commonwealth}}.<ref name="HTFOR12">''[[Halo: The Fall of Reach]]'', ''Chapter 12''</ref> The next three weeks were spent handling a variety of minor missions under her guidance on their way out to [[Chi Ceti IV]] on the edge of [[UNSC]]-controlled space. All of the Spartans worked together to put down multiple insurrectionist factions on [[Jericho VII]] and also to remove a [[black market]] bazaar near the [[Roosevelt military base]].{{Ref/Reuse|HTFOR12}}<ref name="HBB17">''[[Halo: Battle Born]]'', ''Chapter 17''</ref><ref name="Dispatch">[https://www.halowaypoint.com/en-us/news/discovery-dispatch-february-21-2019 '''Halo Waypoint''' - ''Discovery Dispatch'']</ref> 
[[File:TFORAS HalseyWallace.PNG|thumb|350px|Captain Wallace told Doctor Halsey that he might have had her removed from his ship's bridge had its bulkheads not been sealed, in response to what he saw as outbursts against his orders from someone with no combat experience.{{Ref/Reuse|HTFOR12}}]]
It was at 1750 hours on [[2525#November|November 27]] that the ''Commonwealth'' finally emerged in real space in the [[Chi Ceti system]].{{Ref/Reuse|HTFOR12}} Halsey then immediately summoned John to the bridge, where she waited with the ship's Captain [[Wallace]]. The doctor called his attention to a screen displaying deconvoluted radar signals, including one which was repeatedly appearing and might represent another ship eighty million kilometers away. Though Wallace didn't see the need Halsey urged that they go to battle stations and let him and John know that at Harvest the aliens had been observed making an intrasystem slipspace jump, something beyond the capability of human technology. This new information was enough to change the captain's mind and before long the ship had changed its heading and its bulkheads had been sealed. The doctor informed John that they'd be taking one of the ''Commonwealth''{{'}}s dropships to the surface of [[Chi Ceti IV]] and instructed him to get the others ready to depart, seeing as it was vital the Spartans reached Project: MJOLNIR before the [[Covenant]] did. Almost immediately after he'd relayed orders to muster them [[Unrelenting|an alien ship]] [[Maugen-pattern armored cruiser|a third]] the size of the ''Commonwealth'' suddenly appeared three thousand kilometers off its prow. Both vessels quickly engaged one another and Halsey was surprised to see that even a Covenant ship of such small size was equipped with [[energy shielding]]. Even a direct hit from the frigate's [[Magnetic Accelerator Cannon|magnetic accelerator cannon]] only served to disable its shields rather than destroy the ship. Captain Wallace gave orders to ready another round at that, but Halsey argued against this, instead imploring him to initiate evasive maneuvers. Having the doctor second-guess his command led the captain to threaten her with being ''gagged''. Yet soon enough they were been struck amidships by the enemy's weapons and multiple decks had melted in Section One. When fires were reported throughout various sections Catherine suggested the crew don [[respirator pack]]s so the atmosphere could be vented on all decks outside the [[bridge]] and this time, Captain Wallace assented to her recommendation. When he demanded to know what they'd been hit with she explained that the aliens could evidently [[Plasma torpedo|guide]] the trajectory of [[Plasma weaponry|plasma]] through space. Their MAC system having been destroyed, Halsey next floated the idea of attacking with [[Nuclear weapon|nuclear missile]]s but was once more rebuffed by Wallace since the enemy was far too close to them to make their use safe. Both she and John then concluded that using [[GA-TL1 Longsword]]s to distract the aliens could afford them the safe distance they would need to use nuclear weaponry. To their dismay the smaller ship still remained intact, although obviously crippled, after being hit with the blast of a [[Shiva-class nuclear missile|Shiva-class warhead]]. For her part Halsey could at least appreciate that even if they couldn't destroy the enemy's ships they could evidently at least slow them. With the Covenant craft moving off Wallace ordered the ''Commonwealth'' to execute a [[Wikipedia:Planetary flyby|flyby orbit]] so that Halsey and the teenagers could depart for the [[Damascus Materials Testing Facility]] in [[Vhalkem]] as they passed by it. He told the doctor he would attempt to lead the Covenant ship away if it came back but that they should plan to reconvene in orbit no later than 1900 hours. She immediately turned back to John and told him to they needed to hurry, as there was much she had to show the Spartans.{{Ref/Reuse|HTFOR12}}

===MJOLNIR===
{{Quote|Even though this technology will save humanity in [[Human-Covenant War|the war to come]], I must remind myself: liquid crystal cannot rise on its own. [[Titanium]] alloy cannot prevail in the face of extinction. Armor cannot hope. It all means nothing until you step inside.|Halsey shares her thoughts with her Spartans.}}{{Ref/Reuse|BSI}}  
After landing, it took around fifteen minutes for a freight elevator to carry Halsey and the Spartans down into the depths of [[Chi Ceti IV]], finally depositing them in an underground hangar at around 1845 hours.{{Ref/Reuse|HTFOR13}} Catherine only had to clear her throat to garner the attention of the space's three technicians and to make at least a dozen A.I. avatars vanish from view. She then wasted no time introducing the Spartans to Project: MJOLNIR and breaking down the basic parts of the armor suite for them.
{{Expand-section}}

===Alpha Corvi II===
{{Main|Battle of Alpha Corvi II}}
{{Quote|no=three|q1=UNSC Command is pleased... But they still don't trust the Spartan-II project.|Catherine Halsey|q2=So we noticed.|Linda-058|q3=There is concern that your presence will negatively influence marine battle readiness. Luckily for you, Alpha Corvi II provides another chance for you to prove yourselves.|Catherine Halsey|Doctor Halsey provides motivation for John, Fred, Kelly, and Linda.}}<ref name="HCD1">''[[Halo: Collateral Damage]]'', ''[[Halo: Collateral Damage Issue 1|Issue #1]]''</ref>
[[File:HCD1 HalseyJohn.png|300px|thumb|Blue Team's actions on Alpha Corvi II were still not enough to endear Halsey's Spartans to the rest of the UNSC which knew about them, but they had more success in that regard [[Operation: SILENT STORM|a few months later]].{{Ref/Reuse|HCD3}}<ref name="HSS23">''[[Halo: Silent Storm]]'', ''Chapter 23''</ref>]]
On [[2525#December|December 3, 2525]], Halsey met with [[Blue Team]] within the ready room assigned to it on the ''[[UNSC Persian Gate|Persian Gate]]'' while still ''en route'' to the [[Alpha Corvi system]].{{Ref/Reuse|HCD1}} She stated that seeing as they had had the past two days to get used to the idea, in their gut, that a [[Spartan]] fall in battle, it was now time to put their grief aside. She told them that though they should honor that emotion, it would only be a hindrance to the [[Human-Covenant War|upcoming fight]] they were sure to be sorely needed for. [[Lieutenant Commander]] [[Yao]] entered then and took it upon herself to brief the team on the [[Covenant]]'s present [[Battle of Alpha Corvi II|attack]] on [[Alpha Corvi II]]. She explained the role Blue Team was to play in the defense of [[Jamshid]], the planet's largest city, but then left the remainder of the briefing to Halsey. Once Yao had left, Halsey encouraged the four teens by letting them know the [[Mjolnir]] armor had performed better than had been hoped for during the [[Battle of Chi Ceti|engagement]] at [[Chi Ceti IV]] and that much of that had been due to their operating skills. And though she could say that UNSC Command was pleased, she reminded them that the Spartan-II project still wasn't trusted and that there was especially concern that their presence could negatively influence [[marine]] battle readiness. Luckily for them, she offered, Alpha Corvi II just provided another chance for them to prove themselves. Once an [[A.I.]] aboard the ''Persian Gate'' named [[Nora]] provided Doctor Halsey with updated medical scans for each member of Blue Team, she confirmed with John that he was well enough to fight. She also asked whether he would tell her if he wasn't to which he simply said that she'd find out if that ever happened. Taking her leave, she instructed the Spartans to suit up as they'd be exiting slipspace within thirty minutes. She later rejoined them after they'd arrived at the colony to see them off. During the Spartans' insertion via [[D77-TC Pelican]], she remained in contact with them and let them know that while their first priorities were the neutralization of the enemy and the defense of [[Black Reef]], a mining settlement they'd been redirected to after the ''Persian Gate'' was contacted by the ground, she also wanted them to try to find out why the aliens were targeting it specifically. She asked that they pay attention to the enemies' tactics, unit composition, weapons. As the craft drew near its landing zone, she closed by telling the four of them not to expect any help from marines on the ground, as Command didn't want the two groups interacting.{{Ref/Reuse|HCD1}}

Over the course of the engagement that ensued on the surface, Blue Team followed a group of Covenant within the mines beneath Black Reef and contact was eventually lost with them.<ref name="HCD2">''[[Halo: Collateral Damage]]'', ''[[Halo: Collateral Damage Issue 2|Issue #2]]''</ref> Yao was anxious to know what the Spartans were doing and was also overly concerned that they wouldn't be able to escape back to the surface, seeing as the mine entrance they'd entered through had been blown up. Halsey confidently asserted, however, that they were just following their orders and that their resourcefulness should not be underestimated. As the fighting wore on, both planetside and in orbit, the probabilities of both tactical victory and survival of the UNSC fleet began to decrease sharply. At the recommendation of Nora, Yao ordered a general evacuation order for all UNSC personnel on the surface and also ordered for Blue Team to be located so they could provide extraction coordinates. Halsey asked that one Pelican be set aside specifically for her Spartans but Yao just told her to ask again once they reestablished comm contact.{{Ref/Reuse|HCD2}} Blue Team was able to exit the mine by moving underwater toward the shore of the island Black Reef sat on.<ref name="HCD3">''[[Halo: Collateral Damage]]'', ''[[Halo: Collateral Damage Issue 3|Issue #3]]''</ref> Yao, worried, inquired as to whether Mjolnir was designed for submarine operations, to which Halsey admitted it wasn't but surmised that her Spartans must be improvising. The Pelican ''[[Tango 807]]'' collected the team and ferried it back to the ''Persian Gate'' and Halsey met the four of them as they exited. John was incensed that members of the [[United Rebel Front]] who had aided them against the Covenant were being left behind to die, but Halsey tried to make him understand that every fight will always involve some collateral damage and that the most important thing was that he got his team out. She then pushed to find out if he had been able to ascertain what the Covenant had been looking for in the mines. The ''Persian Gate'' jumped from the system a short time later, leaving Alpha Corvi II to the aliens.{{Ref/Reuse|HCD3}}

===A change in tactics===
[[File:HJ Drawing.PNG|thumb|300px|left|Blue Team had encountered [[Sangheili]] on [[Alpha Corvi II]] so it is likely Doctor Halsey also knew of the saurian race when she [[Dr. Halsey's personal journal|drew]] these representations of Covenant species.{{Ref/Reuse|HCD1}}{{Ref/Reuse|HJ22426}}]]
On [[2526#February|February 24, 2526]], Halsey puzzled in her journal over the meaning of the term "Covenant", specifically wondering whether it referred to an agreement between the various species or to a bond believed to be shared between them and a higher power they worshiped.<ref name="HJ22426">''[[Dr. Halsey's personal journal]]'', ''February 24, 2526''</ref> She believed that finding the answer was necessary in order to better understand and exploit the aliens' psychology. In addition, she questioned how many races might belong to the collective that yet remained unknown to humans.{{Ref/Reuse|HJ22426}} On [[2526|March 5 of 2526]] twelve Spartans of [[Gold Team|Gold]], [[Green Team|Green]], and [[Blue Team|Blue]] teams [[Skirmish over Netherop|boarded]] a [[Covenant]] [[Covenant frigate|frigate]] above the uninhabited planet of [[Netherop]] in the [[Ephyra system]].<ref name="HSS2">''[[Halo: Silent Storm]]'', ''Chapter 2''</ref> During the boarding action a sensor operator on a nearby [[prowler]] activated SQUADCOM and gave away the Spartans' presence.<ref name="HSS3">''[[Halo: Silent Storm]]'', ''Chapter 3''</ref> Following the ship's destruction, Halsey shared a portion of their [[TEAMCOM]] download with the responsible crewman and his commanding officer, Lieutenant Commander [[Hector Nyeto]], so that they could hear how the Spartans had reacted to being compromised.<ref name="HSS7">''[[Halo: Silent Storm]]'', ''Chapter 7''</ref> Nyeto later claimed that Halsey had yelled at the operator and by the time she let them both go he was so sick about the mistake that he was volunteering to find [[Daisy-023]] to introduce himself.{{Ref/Reuse|HSS7}} Unknown to Halsey then, the activation had actually been intentional, as Nyeto and those loyal to him wanted the Spartans killed on behalf of the [[Insurrection]].{{Ref/Reuse|HSS23}}

===SILENT STORM===
{{Quote|no=four|q1=The UNSC has two choices at the moment, the one rotten and the other lousy. Either we engage the enemy right now and start losing fleets in battles we have no chance of winning, or we mass at strong points and let the enemy glass everything else.|Preston Cole|q2=I should think the answer is obvious. We mass at the strong points. It will take the Covenant ''at least'' two years to locate all of our undefended worlds, and by then the Materials Group will have reverse-engineered—|Catherine Halsey|q3=Catherine, FLEETCOM can't ''do'' that. We'd be leaving hundreds of worlds defenseless. We'd be condemning billions of colonists to death by plasma incineration.|Michael Stanforth|q4=And if you commit prematurely, you will lose every fleet you send—and leave hundreds of worlds defenseless anyway. I think you need to make FLEETCOM understand that, Admiral Stanforth. There is nothing you can do to save those people—not until I can give you the tools you need to fight.|Catherine Halsey|Doctor Halsey argues, unsuccessfully, for a strategy that would sacrifice billions but conserve military losses.}}{{Ref/Reuse|HSS4}}
By [[2526#March|March 7]] she was aboard the {{Class|Valiant|super-heavy cruiser}} {{UNSCShip|Everest}} within a deep space transitional zone of the [[Dynizi system]].<ref name="HSS4">''[[Halo: Silent Storm]]'', ''Chapter 4''</ref> At shortly after 0840 hours, in a compartment located within the Flag Deck's secure conference suite, Halsey met with vice admirals Stanforth and [[Preston Cole]], who commanded the ''Everest''. The three of them had met to plan a means by which the Navy could feasibly fight back against the Covenant. Catherine had also concluded that [[Staff Sergeant]] [[Avery Johnson]] of the [[UNSC Marine Corps|Marine Corps]] would also be a valuable asset to have at their disposal, so he soon joined the meeting as well. When Johnson entered the room he found Halsey forcefully arguing the necessity of another attempt at capturing a [[Covenant]] ship, [[Skirmish over Netherop|such a mission]] having been recently tried and failed by twelve of her Spartans. She argued that it was of paramount importance that they gathered as much of the aliens' technology as they could, since she believed the only way to beat the aggressors was through reverse-engineering it. She also was of the opinion that the best strategy at that moment would involve massing fleets at strong points, leaving most colonies undefended while she and others within ONI's [[Materials Group]] worked over the next year or two to deliver the ability to fight back. Halsey implored Stanforth to make FLEETCOM understand this, but ultimately backed down and admitted that she had been making assumptions about the aliens' strategy that were unjustified with what little they knew about them. In the face of this admission, however, she stressed once more the importance of capturing an enemy vessel. As far as she was concerned the recent try had not been a total failure thanks to the capture of a few [[Type-26 Banshee]]s and the destruction of [[Radiant Arrow|the ship]]. It was with reluctance that Halsey finally agreed such an acquisition couldn't be the prime objective of the [[Operation: SILENT STORM|upcoming operation]]—it would need to be secondary to blunting the enemy's advance against their worlds. When the conversation eventually turned to why Avery had been handpicked to assist with this op Halsey reminded him of his experience [[First Battle of Harvest|fighting]] the Covenant just a little over a year prior and his history as an [[ORION Project]] volunteer. She had hoped his [[Special operations]] background and creativity exhibited at [[Harvest]] would lend themselves to the creation of new infiltration tactics for each ship they targeted. Additionally, the doctor pointed out that his experiences with ORION made him able to relate to the Spartans, introducing the sergeant to what they were and how they had been trained. Stanforth described Johnson's role to be a sort of "big brother" to the Spartans during the mission, with Halsey making sure he understood he'd never be able to replace [[John-117|their squad leader]].{{Ref/Reuse|HSS4}}

The next day Halsey joined Johnson and both admirals aboard the {{class|Point Blank|prowler}} {{UNSCShip|Vanishing Point}} in deep space within the [[Polona sector]].<ref name="HSS5">''[[Halo: Silent Storm]]'', ''Chapter 5''</ref> At 0558 hours she led [[John-117]] into the ship's tactical planning center for a meeting with the aforementioned men, Captain [[Halima Ascot]], and [[Colonel]] [[Marmon Crowther]], commander of the [[21st Space Assault Battalion]] of [[ODST|orbital drop shock trooper]]s. Halsey took the first open chair around the TPC's conference table and before long was being introduced by Cole as leading their effort to analyze and reverse-engineer alien tech. The mission those present had gathered to discuss, [[Operation: SILENT STORM]], was being conceived of as a desperate mission with the stated aim of boarding as many Covenant capital ships as possible in order to detonate small-yield tactical [[nuclear weapon]]s within their hulls. When Colonel Crowther balked at these aims, Halsey suggested that John be put in command of his troopers. She had previously broached this suggestion with Cole, who rebuffed it for a second time, stating that John was not ready to lead something of that scale. Halsey began to argue in kind but was cut of by John himself, who agreed with the admiral. This earned him a scowl from the doctor but she did not press the point any further after that. Ascot, who would be leading an all [[prowler]] force dubbed [[Task Force Yama]], let Halsey know she would be confined to the ''Vanishing Point'' for her own safety for the operation's duration. Halsey began to protest this but relented when Cole threatened to ship her back to [[Reach]] should she try to leave the ship.{{Ref/Reuse|HSS5}} Following this meeting Catherine gave Johnson access to the Spartans' TEAMCOM to facilitate his role as liaison between they and the ODSTs and also made it clear to John that he should give the sergeant's advice a lot of weight—especially when navigating the vagaries of protocol inherent in their attachment to the 21st.{{Ref/Reuse|HSS7}}<ref name="HSS8">''[[Halo: Silent Storm]]'', ''Chapter 8''</ref>

===Seoba===
{{Main|Battle of Seoba}}
[[Task Force Yama]] reached the [[Kolaqoa system]] and the planet [[Biko]]'s third moon, [[Seoba]], on March 18.{{Ref/Reuse|HSS7}} Seeing as Biko lay right in the path of the enemy's current invasion route, it had been picked as the perfect spot to lie in wait for the Covenant.{{Ref/Reuse|HSS5}} The task force was soon met with resistance from insurrectionists working in concert with the [[Biko Independence Army]] during its [[Operation: ICE DANCE|insertion]] of Spartans and ODSTs to an abandoned [[Seoba Ice Quarry|ice quarry]] on the moon.{{Ref/Reuse|HSS8}} 

The following day, Halsey was transported from the ''Vanishing Point'' for an impromptu after action debriefing held around a folding conference table within [[Assembly Chamber 4L430]] in one of the quarry's abandoned habitats.<ref name="HSS11">''[[Halo: Silent Storm]]'', ''Chapter 11''</ref> She was seated between Captain Ascot and Colonel Crowther; also present were Captain [[Nelly Hamm]], Sergeant Johnson, Lieutenant Commander Nyeto, and John-117, who the debriefing principally concerned. During [[Ghost Flight]]'s insertion [[Alpha Company (Black Daggers)|Alpha Company]] had taken on an inordinate amount of casualties, and the unorthodox manner in which John had partially led that drop was being questioned. Halsey pushed back against the very notion that anything had gone wrong with the drop, seeing as the dockyards had been captured in less than an hour. She was surprised to hear, however, that it appeared the enemy had been expecting them. Regardless, Captain Hamm claimed that while still in the {{UNSCShip|Ghost Song}} John had dumped a wounded trooper in her lap for the sole purpose of keeping her preoccupied so he could do things as he saw fit. Halsey was quick to defend him, but John confirmed the captain's accusation. Nyeto also spoke in John's defense, but in doing so let on that he may be younger than the age currently being claimed for him. As the conversation shifted to this matter Halsey protested its relevance and told Captain Ascot the true ages of the Spartans were compartmentalized and classified Top Secret Level One. She also assured her, however, that their training and judgment was unparalleled. Despite her efforts at further concealment the lieutenant commander explained how he'd realized the Spartans must all be around fifteen years old then. He claimed to have a friend who had trained with a bunch of eight-year-olds on [[Reach]] seven years prior. Halsey responded by leaning forward so her upper body shielded Nyeto from Ascot demanded how he could know those eight-year-olds were her Spartans, and once again it was John's inability to convincingly lie that had given away the truth. The doctor was finally forced to resort to saying the Spartans' ages could not leave the room, but Colonel Crowther was quick to threaten her with incarceration for violations of the [[Uniform Code of Military Justice]]. Catherine asked the man if he really thought his superiors would let the [[Judge Advocate General]] hear about this before emphatically declaring that despite their youth, the Spartans were ''not'' children. Ascot and Crowther determined that they were to be sidelined for the remaining duration of SILENT STORM—something Halsey strongly urged them to reconsider.{{Ref/Reuse|HSS11}}

After a long silence, the debriefing returned once more to the matter of Alpha Company's casualties. This soon led the discussion to the topic of how the insurrectionists had seemingly been ready for their arrival, with John realizing and convincing the others that they had instead been waiting for the Covenant, with the intent to meet them for negotiations. While they were planning for the Covenant's inevitable arrival, [[Bloodstar Flotilla|a flotilla]] of the alien ships arrived in-system and set course for Seoba. As the UNSC leaders rushed out of the chamber to ready their forces, John offered the assistance of he and his Spartans for the task force's boarding attempts, with Halsey vouching that this kind of mission is exactly what she created them for. Still, Crowther refused and ordered John and his compatriots to load the roughly 300 captured insurgents onto [[Emmeline|a transport]] to be sent to Biko. After John accepted the assignment, they all left the chamber and Halsey was transported back to the ''Vanishing Point'', which had moved to a safer position two planetary orbits out from Biko.{{Ref/Reuse|HSS11}} 

In the ensuing battle, Captain Ascot's {{UNSCShip|Starry Night}} was shot down and John decided that they would search for survivors, as the Spartans were the only unit readily available to assist.{{Ref/Novel|Id=HSS13|HSS|Chapter=13}} Back in the quarry, they found the prowler's crash site, but [[Worthy Silence|an]] [[intrusion corvette]] was seemingly attempting to recover it. Since the data within its computer systems could present a major security risk if acquired by the Covenant, John decided that they would activate the ''Starry Night''{{'}}s [[self-destruct]].{{Ref/Novel|Id=HSS14|HSS|Chapter=14}} While the Spartans experienced some setbacks and injuries during their attempt at boarding the prowler, a team led by Fred-104 made their way inside, rescued some survivors, and armed its [[Fury tactical nuclear weapon|Fury nuke]]. The resulting explosion destroyed both the prowler and the intrusion corvette. However, the alien vessel's forward fuselage was left mostly intact,{{Ref/Novel|Id=HSS15|HSS|Chapter=15}} allowing the Spartans to search it for any salvageable technology. Sure enough, they found a functional [[Kelguid|starholo]] and removed it, bringing the device back to Halsey for her to examine.{{Ref/Novel|Id=HSS16|HSS|Chapter=16}}

The next day, after spending some time with the starholo, Halsey attended a funeral service on the ''Vanishing Point'' to honor the men and women of the UNSC Navy who lost their lives at Seoba. She stood near John and the five other Spartans who were not relegated to the ship's infirmary. After the ceremony, Hector Nyeto—now the de facto commander of Task Force Yama after Ascot's death—approached John to complement him and his team on preventing the Covenant from capturing the prowler. When Halsey pointed out that they had also managed to destroy a corvette, Nyeto enthusiastically added that they had also recovered the starholo, clearly trying to get on her good side. He then made a comment on how she might deduce something useful from the alien machine, to which she responded with a calculated smile. Because of Nyeto's seeming appreciation for the Spartan-IIs, John asked him if he would reconsider their sidelining. The lieutenant commander promised that they would see all the action they could handle, prompting Colonel Crowther to deny this one more due to their young age and the fact that the Spartans reported to him. This resulted in a shouting match between the two officers that ended in Nyeto relenting after being threatened with a report to a board of inquiry. After this shocking exchange, Halsey grabbed John by the arm and directed the Spartans out of the hangar toward the Black Daggers' quarters.{{Ref/Reuse|HSS16}}

Later that day, the Covenant's [[Fleet of Inexorable Obedience]] arrived in the Kolaqoa system and began their [[Battle of Biko|assault]] on Biko. As Task Force Yama and the Black Daggers joined the battle, Colonel Crowther sent Staff Sergeant Johnson to give the Spartans their new orders on the UNSC ''Vanishing Point''. Informing them of the colonel's suspicions toward Lieutenant Commander Nyeto, Johnson told the Spartans that Crowther was sending them to [[Etalan]] to attack a small logistics fleet supporting the main element at Biko.{{Ref/Novel|Id=HSS17|HSS|Chapter=17}} A few hours later, Halsey, Johnson, and the Spartans entered slipspace aboard the ''Vanishing Point'' with a course set for the [[Igdras system]].{{Ref/Novel|Id=HSS19|HSS|Chapter=19}}

===Etalan===
{{Main|Battle over Etalan}}
On [[2526#March|March 22, 2526]], the ''Vanishing Point'' and its two prowler escorts arrived at Etalan to find a logistics fleet of fifteen Covenant vessels orbiting the planet. During the two-day trip, John-117 and Johnson had determined that they would target the fleet's munitions and food supplies, assuming they could identify which ship served each role. About five minutes after the detachment began observing the alien vessels, Halsey had already theorized that the trio of [[Bladder ship|large vessel]]s dipping in and out of Etalan's upper atmosphere were the munitions carriers, collecting and refining the gas needed to synthesize the fleet's [[plasma]]. However, Halsey did not share this theory with anyone else for fear of it leaking to Insurrectionist spies serving under Hector Nyeto. For the next four days, the ''Vanishing Point''{{'}}s analysts would continue their observations of the fleet until they were confident that four of the vessels acted as equipment freighters. Gold and Green Teams were [[Battle over Etalan|deployed]] via [[S-14 Baselard]]s to attempt to board and destroy these ships from the inside using HAVOK nuclear weapons. Meanwhile, Johnson and Blue Team prepped to enact their own plan to destroy what the analysts believed to be {{Pattern|Mjern|agricultural support ship}}s. Before they deployed in the Banshees they had captured during their attack on the ''Radiant Arrow'' a few weeks prior, Halsey visited them in one of the ''Vanishing Point''{{'}}s hangars. She informed the Spartans that they should target the three "air-skimmers" and that she had realized Nyeto and those serving under him were aligned with the Insurrectionists when the lieutenant commander revealed John's true age at Seoba. In the time since then, Halsey had also found various surveillance devices hidden in her lab. Halsey then mentioned to them that she had made some progress on deciphering the captured starholo, and that crippling the logistics fleet and forcing the Fleet of Inexorable Obedience to fall back to resupply would help her narrow down the location of the Covenant's primary supply depot in the region.{{Ref/Reuse|HSS19}}
{{Expand-section}}

===Naraka===
{{Quote|no=four|q1=Habitable worlds create gravity wells, and there aren't any—not within four days of the most likely transit nodes.|Catherine Halsey|q2=But there is a habitable world within five days of Transit Node Bhadra. Perhaps it's not my calculations that are mistaken, but ''your'' assumption.|Déjà|q3=Are you suggesting the Covenant has instantaneous interstellar communications?|Catherine Halsey|q4=I am suggesting the Covenant has a great deal of... technology that we don't... understand.|Déjà|Déjà brings Halsey to the right conclusion based on the evidence, despite being slowed by a data miner.}}{{Ref/Reuse|HSS22}}
At 0626 hours on [[2526#March|March 31]] Halsey was in the middle of studying the captured starholo.<ref name="HSS22">''[[Halo: Silent Storm]]'', ''Chapter 22''</ref> The ''Vanishing Point'' had relocated to the deep space Rendezvous Point Sierra-Yama within the [[Polona sector]]. With a little luck and lots of hard work, the doctor was hoping she could trace the Covenant's slipspace routes back to the [[Fleet of Inexorable Obedience|invasion fleet]]'s primary [[Zhoist|supply depot]]. By this point she had already identified more than twenty transit nodes which opened near what she believed were [[Etalan]], [[Harvest]], and [[Netherop]], and four of these were near other nodes which led out of human-controlled space. Five days had passed before a new supply convoy had arrived at Etalan following the previous one's destruction, so Halsey surmised its point of origin had to be somewhere between one-half and three-quarters of that distance at the aliens' slipspace travel rates. She asked [[Déjà]] how certain the A.I. was about the size of the logistics base that the Covenant fleet must require, but she only reconfirmed what had already been calculated previously. Catherine was flummoxed, since there simply weren't any habitable worlds within four days of the likely transit nodes. Déjà deigned to point out there was one within ''five'' days of [[Transit Node Bhadra]], however. Implicit in this observation was the idea that the Covenant must have instantaneous interstellar communications.{{Ref/Reuse|HSS22}} 

By this point Catherine had discovered a data miner had been slipped into her quarantined lab by Hector Nyeto or one of his operatives.{{Ref/Reuse|HSS22}} It was causing Déjà to make erratic pauses while speaking and had already stolen her most closely guarded data, but Halsey was tolerating it because she didn't want Nyeto to know she had noticed it yet. Nonetheless, the doctor agreed with what Déjà was suggesting and determined they ought to proceed to Transit Node Bhadra. With that settled the A.I. notified her Colonel Crowther had finally arrived. Catherine deactivated the starholo and ran her fingers through her hair briefly before meeting the colonel at her door. She'd sent him a message asking him to meet her there as soon as their rendezvous was complete for a "personal matter", and now that he'd shown up she feigned delight at his presence and took his arm to draw him toward her personal quarters. She confessed to being unable to wait any longer to be alone with him and made sure to press her flank against his as she pulled him through the other door into her little galley area. Once they were both sealed within, however, she released him and said she only needed to talk someplace safe. She let him know she swept for eavesdropping devices within her quarters three times daily and had found nothing so far. She offered the men water and apologized for leading him along before stating they needed to discuss how they were going to handle Nyeto before he tried to kill her Spartans again.{{Ref/Reuse|HSS22}}

Through researching Nyeto's records Catherine learned he had spent a lot of time with the infamous [[Robert Watts]] early in his career.<ref name="HSS23"/> She and Crowther told John that though they would leave him alone as the task force's commander for the time being, they planned on using him to mislead the enemy. Despite the improved slipspace efficiencies afforded by Doctor Halsey's understanding of the alien starholo, it still took the task force time to arrive at Transit Node Bhadra, more than two hundred light-years past humanity's farthest known exploration. It was Halsey who had named the transit node, and she likewise chose to call the [[sector]] of Covenant space they were invading by 0458 hours on April 14 [[Muruga sector|Muruga]], both [[Religion|Hindu]] names meant to honor Captain Ascot. Their target planet and its moon she called [[Naraka]] and [[Rudara]], respectively.{{Ref/Reuse|HSS23}} By April 15 Halsey had viewed reconnaissance videos which showed Naraka was encircled by a [[Ring of Mighty Abundance|ring]] of orbital support stations connected by a transit tube enclosed within what she called a trussing armature.<ref name="HSS25">''[[Halo: Silent Storm]]'', ''Chapter 25''</ref> In her estimation, if [[Sierra Force]] could destroy at least ten facilities and their connecting armature there was a ninety-two percent chance the ring's orbit would grow unstable and fall into a rapid, irreversible decay.{{Ref/Reuse|HSS25}} If only nine were destroyed, she predicted the odds of that happening dropped to seventy-one percent, and if only seven, forty-nine percent.<ref name="HSS27">''[[Halo: Silent Storm]]'', ''Chapter 27''</ref> Ultimately, [[Operation: SILENT STORM]] scored a giant win for the UNSC when the orbital ring was successfully brought down thanks to her Spartans and Crowther's ODSTs, but the colonel lost his life and Hector Nyeto fled from the rest of the task force during the mission.{{Ref/Reuse|HSS27}}

===Total War===
[[File:HalseyJournalNode.PNG|thumb|300px|Doctor Halsey considered the [[Wikipedia:Dendrite (mathematics)|dendritic]] growth of cross-connections in volitional A.I.s near the ends of their lives to be akin to the spread of [[Wikipedia:Cancer|cancer]] in biological organisms.{{Ref/Reuse|HJ5326}}]]
{{Quote|[[Michael Stanforth|Vice admiral]] ordered us to repurpose ''everything'' to quell the Covenant threat, and to refocus our research on wartime strategy. I couldn't agree more (it was, after all, my idea).|Catherine takes note of the UNSC's shift in priorities within her [[Dr. Halsey's personal journal|journal]].}}{{Ref/Reuse|HJ42826}}
Thirteen days later, on [[2526#April|April 28]], Halsey noted in her journal that Vice Admiral Stanforth had ordered she and others to repurpose everything to quell the [[Covenant]] threat and to refocus their research on wartime strategy.<ref name="HJ42826">''[[Dr. Halsey's personal journal]]'', ''April 28, 2526''</ref> She couldn't have agreed more, seeing as doing just that had been her idea to begin with, though she did sarcastically ask if the [[Insurrection]] would adhere to the policy as well. By this time Halsey had learned [[ONI]] [[ONI Section Two|Section Two]] had sent emissaries to leaders in the [[Outer Colonies]] to warn them of the Covenant and to make them offers of peace. Footage from the [[Battle of Bliss|glassing]] of [[Bliss]] generally convinced these leaders of the magnitude of the threat they all faced. In her journal Halsey wondered if the aliens might have solved their civil war—not a trade she would have made, but perhaps a small victory nonetheless.{{Ref/Reuse|HJ42826}} On [[2526#May|May 3]] Catherine reviewed in her journal the distinctions between so-called "[[Smart AI|"smart"]] (volitional) and [[Dumb AI|"dumb"]] artificial intelligences and why the "smart" ones are susceptible to [[rampancy]].<ref name="HJ5326">''[[Dr. Halsey's personal journal]]'', ''May 3, 2526''</ref> She noted that she had devised new matrix strata with random-access optical couplers that could theoretically extend a volitional A.I.'s lifespan, though by exactly how much she was unsure. In simulations a randomly coupled matrix also boosted correlation effects such as accurate guessing. As volitional A.I.s were needed then more than ever to counter the Covenant threat, Vice Admiral [[Michael Stanforth|Stanforth]] had authorized a test run of Halsey's protocols. After leaving herself a reminder to investigate the polarization of topological [[Wikipedia:Soliton|soliton]] pulse transfers she concluded that day's writing by questioning whether she was playing the role of [[Wikipedia:God|God]] or mother in breeding life from non-life, or perhaps simply being beguiled by sentimental anthropomorphism.{{Ref/Reuse|HJ5326}}

Near the start of May [[John-117]] told Halsey he suspected the Covenant had created a special Spartan-hunting unit based on encounters he'd had with [[Bloodstars|well-trained warriors]] in distinctive armor during Operation: SILENT STORM.<ref name="HO4">'''[[Halo: Oblivion]]''', ''Chapter 4''</ref> In response the doctor immediately distributed a list of precautions and procedures she wanted implemented whenever her Spartans were in a combat theater. On [[2526#June|June 3]] [[Task Force Pantea]], a wolf pack of [[Battle Group X-Ray]], managed to knock out the shields and primary weapons of [[Steadfast Strike|a]] [[Covenant frigate]] and seemingly ground it on [[Netherop]]. At least a day later, it was determined that [[Blue Team]] would be deployed to the planet to aid an [[ONI]] salvage ship, the {{UNSCShip|Phyllis Wheatley}}, in an attempt to capture the enemy vessel. Halsey recorded a message for John in which she acknowledged the entire situation was likely a trap but stated she wanted the Spartans to secure the alien ship anyway. A fully functional Covenant vessel could give the UNSC the knowledge needed to develop effective countermeasures. The doctor reminded him how important the [[kelguid|starholo]] recovered on [[Seoba]] had been to SILENT STORM and emphatically made clear that the downed frigate, dubbed the "''[[Steadfast Strike|Lucky Break]]''", was a thousand times more important before wishing him safe travels.{{Ref/Reuse|HO4}} Unfortunately, the [[Battle of Netherop|mission]] did not result in success for the UNSC.<ref name="HOE">''[[Halo: Oblivion]]'', ''Epilogue''</ref> Following the failed effort Catherine reported to interior compartment of the [[Wikipedia:Chester W. Nimitz|Chester W. Nimitz]] Secure Conference Suite aboard the ''[[UNSC Everest|Everest]]'' on June 12, then located at [[Rendezvous Point Durga]] within a deep space transitional zone of the [[Polona sector]]. She was joined by Vice Admirals [[Preston Cole|Cole]] and [[Michael Stanforth|Stanforth]], Lieutenant [[J. Stone]] and Lieutenant Commander [[B. Nett]] (both of the [[UNSC Judge Advocate General's Corps|Judge Advocate General's Corps]]), two young people who had been among those discovered living on Netherop's surface during the operation, and John, who was the last to arrive at 1010 hours. They had gathered for a Court of Inquiry meant to clarify what precisely had gone wrong and how [[prowler]] captain [[Amalea Petrov]], commander of the {{UNSCShip|Night Watch}}, had been marooned on the planet. Halsey disputed Admiral Cole's characterization of the mission as a failure, seeing as the ''Lucky Break'' seemed to have always been a trap—one perhaps meant to capture Spartans—that had not borne fruit for the Covenant. She also pointed out that they'd recovered a [[Sangheili personal energy shield|personal shield generator]] of a type unseen up to that point. Cole, for his part, was less optimisitc since it would likely be years before any useful battlefield technology resulted from that acquisition. She assured him she was moving as fast as she could with her work. The court soon turned to the matter of what ought to be done with [[Castoffs|the young people]] found surviving on Netherop, previously thought to be uninhabited. The representatives present, [[Samson]] and [[Roselle]], petitioned the UNSC brass to let them start new lives on [[Gao]], but both Halsey and Stanforth were reluctant to indulge their request. Admiral Cole and Lieuetenant Stone were more sympathetic, however, and they were ultimately permitted to relocate to the outer colony.{{Ref/Reuse|HOE}}

At some point after her Spartans begin racking up successes, Halsey's meager budget mushroomed overnight and she was once again offered a corner office in [[Olympic Tower]].{{Ref/Reuse|HTFOR25}} She declined the offer for the second time, however, as she enjoyed the fact that someone had to spend a half a day getting through various security barriers to meet with her. Her original banishment, as she saw it, had become a bureaucratic weapon for her.{{Ref/Reuse|HTFOR25}} At some point in late [[2526]] Halsey caught up to [[Soren-066]] and Chief Mendez as the two were conversing while walking in a hall on Reach.<ref name="HEP6">''[[Halo: Evolutions]]'', ''[[Pariah]]'', ''Chapter 6''</ref><ref name="HEP7">''[[Halo: Evolutions]]'', ''[[Pariah]]'', ''Chapter 7''</ref> The Chief had been explaining why active service was no longer an option for the boy and Halsey jumped in to back him up, emphasizing that Mendez had to do what was best for the program and the others trained in it. The doctor promised he would still be able to serve in a non-combat role and regretfully apologized when he asked why she was no longer allowing him to make choices.{{Ref/Reuse|HEP6}} At some point more than six months after she told Soren that hard truth, the teen helped [[Partch|a]] technician at the compound steal a [[GA-TL1 Longsword]].{{Ref/Reuse|HEP7}}<ref name="HEP9">''[[Halo: Evolutions]]'', ''[[Pariah]]'', ''Chapter 9''</ref> They did not get far, however, and Soren was forced to crash-land the fighter.{{Ref/Reuse|HEP9}} Chief Mendez paid a visit to Halsey in her office after visiting the site and looking through the wreckage and let her know that no signs of Soren were present.<ref name="HEPE">''[[Halo: Evolutions]]'', ''[[Pariah]]'', ''Epilogue''</ref> Only his accomplice's body was found. Halsey vowed to look into how this technician—[[Partch]]—had gotten into the position he'd held, given that his background showed all the earmarks of an [[insurrectionist]]. Mendez recommended she run another background check on everyone higher up in security. Halsey then stopped him before he could start smoking right there in her office and asked if there was anything else to discuss. The chief went on to relay further details about parts torn free of the fighter which had landed elsewhere, but despite there being no sign of Soren among them either, he thought it unlikely the boy could have survived. When Halsey asked how [[Randall Aiken|Randall-037]]—who had unsuccessfully tried to stop Partch and Soren—was doing, Franklin claimed he was fine. After being told that ground troops had been dispatched to comb the woods for a body the doctor told him to pull them back and have Soren filed as [[missing in action]]. She wagered that he was still alive, but based on her experience with him that meant he would only ever be found if he wanted to be. Mendez started to protest but she reached across her desk to touch his arm and urged him to let him go, arguing he was not a threat to them. Mendez pointed out that he had been a trained and augmented as Spartan and now had rebel sympathies, but Halsey only replied that he was no [[Treason|traitor]]; just a lost soul looking for direction.{{Ref/Reuse|HEPE}}[[File:DevilDrawing.PNG|left|200px|thumb|Doctor Halsey sketched this image based on her observations of [[Araqiel|the A.I.]] [[Section Three]] employed to spy on her.{{Ref/Reuse|HJ71231}}]]
On [[2529#December|December 11, 2529]] Halsey recorded that she'd had limited success using the [[Illegal Entry Protocols|illegal entry protocols]] to access a nonessential subroutine in a recovered [[Kig-Yar]] [[Kig-Yar point defense gauntlet|point defense gauntlet]].{{Ref/Reuse|HJ121129}} The details of her success were published as part of the work of another researcher, Doctor [[Hardy]], who had been studying the gauntlet. Unfortunately, it was demonstrated that using the protocols in this way accelerated the terminal cross-linkage effect of her A.I.s. [[Jerrod]], a [[Artificial intelligence#"Micro" AI|micro-A.I.]] in her employ, believed he had a solution to this predicament.{{Ref/Reuse|HJ121129}}<ref name="HGOO16">''[[Halo: Ghosts of Onyx]]'', ''Chapter 16''</ref> Halsey was skeptical, but agreed to proceed according to his advice with caution.<ref name="HJ121129">''[[Dr. Halsey's personal journal]]'', ''December 11, 2529''</ref> On [[2530#April|April 9, 2530]] the doctor made note that Chief [[Franklin Mendez|Mendez]] was incommunicado and that nobody seemed to know his whereabouts.<ref name="HJ4930">''[[Dr. Halsey's personal journal]]'', ''April 9, 2530''</ref> She decided to continue monitoring this development, as she felt something must be wrong to have pulled him off her radar like this.{{Ref/Reuse|HJ4930}} At some point prior to [[2531]] Halsey took on at least one student, [[Ellen Anders]].<ref name="HWPOM">''[[Halo Wars]]'' ''[[Planetary Operations Manual]]''</ref> The two had a mutual hate for one another according to Anders' later recollection.{{Ref/Reuse|HWPOM}} On [[2531#July|July 12, 2531]], Halsey noted that Section Three had begun to use [[Araqiel|a]] new-generation A.I. of its own to conduct surveillance and protect its assets.{{Ref/Reuse|HJ71231}} She had noticed that her network codes, keystroke style, and even her voiceprint all triggered its counter-intrusion measures. Though she could devote time to clandestinely pursuing this to sate her curiosity, she knew she'd be detected. As such, she was left to just wonder [[SPARTAN-III program|what]] ONI was hiding from her. It was by this date as well that [[Jacob Keyes]] had agreed to take in [[Miranda Keyes|Miranda]], which her mother figured would be for the best.<ref name="HJ71231">''[[Dr. Halsey's personal journal]]'', ''July 12, 2531''</ref> By the end of October that year, Halsey had recently purchased upgrades for her Spartans' microfusion plants.<ref name="HGOO2">''[[Halo: Ghosts of Onyx]]'', ''Chapter 2''</ref> On [[2532#January|January 18, 2532]], Halsey recorded her thoughts upon learning that several of the chemical precursors used in [[Project ASTER|Project: ASTER]] had been routed to Section Three laboratories on [[Algolis]], [[Meridian]], and [[Ariel]].<ref name="HJ11832">''[[Dr. Halsey's personal journal]]'', ''January 18, 2532''</ref> She was enraged at the possibility that the Spartan-II program might be being [[Spartan-III program|replicated]] without her guidance and couldn't fathom what the implications of that might be. She made sure to track all those who had "washed out" during the augmentation procedures in [[2525]] but as far as she could tell, none of them had been repurposed. Those that had been rehabilitated were on track to be recommitted soon and whatever was going on, she reasoned, must not involve them. The doctor noted the peril at which she was maneuvering outside of Stanforth's protection and the terms of her charter. She figured her enemies must think the threat of being charged with espionage or with the violation of any particular military regulation would keep her from pursuing leads in order to preserve her position, but she judged that to be an underestimation of her.{{Ref/Reuse|HJ11832}}

===Research Advancements===
[[File:MJOLNIR.PNG|thumb|300px|By [[2535#January|January 7, 2535]] Halsey had turned over the fourteen existing variations of Mjolnir to Vice Admiral Stanforth at his request.{{Ref/Reuse|HJ1735}}]] 
{{Quote|The [[Illegal Entry Protocols|illegal entry protocol]]s ("PIE") used for hacking insurgent networks have deciphered a tiny portion of the aforementioned Jackal shield system. Just goes to show that no scrap of genius goes wasted! I've had [[Jerrod]] dedicated all his runtime to further avenues of inquiry—perhaps they can crack more. Already have enough data to run a simulated test for a Mjolnir energy shield system. Moreover, if we can understand their operating systems, we hope to gain insights into their language (their motivations?). ''That'' might prove ultimately of more value than any weapon we could devise.|Catherine Halsey responds to a major breakthrough with enthusiasm.}}{{Ref/Reuse|HJ52044}}
By [[2533#November|November 10, 2533]] Catherine had developed a new theoretical architecture which involved three [[artificial intelligence]]s arranged in parallel.<ref name="HJ111033">''[[Dr. Halsey's personal journal]]'', ''November 10, 2533''</ref> She did this in order to palliate the preemptive severing of neural linkages and ultimate self-termination which characterized third-generation A.I.s, hoping that by leaving all choices to be decided by majority vote the frenzied cutting behavior would be avoided. In her design, ties which arose when one of the A.I.s abstained would resolve at random. Though Halsey knew this could slow overall processing, she was confident such a theoretical trio would deconvolute and divide algorithms to compensate for the loss, and in doing so perhaps even ''accelerate'' processing. Consensus-based decision-making would also be applied to linkage creation in order to forge a superior initial neural linkage. Unfortunately, Halsey could not know how the theoretical trio's overall lifespan might be increased under such circumstances because simulations could not create ''[[Wikipedia:In vivo|in vivo]]'' A.I.s. Writing in her journal on that November [[2533]] date, the doctor wondered what other characteristics could emerge from an A.I. triumvirate. She only had three at her disposal at the time and as such had moved them to the [[Sanderson Private Hospital|Sanderson private hospital]] on [[Beta Hydri VI]] as a precautionary measure. In addition, she kept all knowledge of this from other A.I.s she interacted with. A note from Halsey to herself on November 10 served as a reminder to follow up on reports of [[Mack|nes]][[Loki|ted]] A.I. personalities that were present on [[Harvest]] before it was [[First Battle of Harvest|lost]].{{Ref/Reuse|HJ111033}} A little over a year later, on [[2534#December|December 25, 2534]], Halsey recorded her thoughts concerning an interaction she'd had with a colleague, Doctor [[Forester]], in which she had illustrated increasingly complex sketches for him with the intent to visualize conceptions of space with increasing hyperdimensions.<ref name="HJ122534">''[[Dr. Halsey's personal journal]]'', ''December 25, 2534''</ref> She had been attempting to show him that it was the increased density of cross-linkages which caused wave function collapse, not the creation of the links themselves. If space were not a limiting factor the number of available connections would increase at a geometric rate. Though Halsey considered classic [[Wikipedia:String theory|string theory]] dubious, she thought the eleven (or more) dimensions it predicted could theoretically be accessed by anyone outside the quantum fields which enveloped ships traveling through [[slipspace]]. She was disappointed Doctor Forester apparently failed to grasp that slipspace was open to exploitation within four-dimensional [[Wikipedia:Spacetime|spacetime]]. Writing in her journal following their discussion, Catherine pondered whether remote construction with any exotic matter in the raw slipstream was possible, for at that moment the technology required for that remained at best theoretical. She figured decades or even centuries may pass before the necessary tech and its practical applications arrived. She closed that day's entry wondering whether people were ready for the potentially near-limitless cross-connections and faster-than-light processing speeds A.I.s in slipspace could possess.{{Ref/Reuse|HJ122534}}

By [[2535#January|January 7, 2535]] Catherine had reminded Admiral Stanforth at a budget meeting that continuous upgrades were integral to the Mjolnir system if they expected it to shatter technological barriers as a pioneering effort (something she'd thought they'd both agreed upon).<ref name="HJ1735">''[[Dr. Halsey's personal journal]]'', ''January 7, 2535''</ref> To her dismay, she was told this would no longer be possible since the military required a simplified generational system to categorize, prioritize, and serialize the project for fiscal year budgets. Halsey agreed to cooperate with this stipulation but determined she would by no means wait on breakthroughs just to fit accountants' calendars. She understood she was working with systematic impediments, and on January 7 put down in her journal her preliminary modularization of upgrades for MJOLNIR with the expectation that the entries could and likely would be modified or reconfigured as time, budget, and other limitations cropped up. She also considered that a reevaluation may be in order as new technologies and limitations manifested—especially if the Covenant noninstrumentality problem was cracked. In particular she had to wonder whether [[energy shield]]ing would be possible for the [[MJOLNIR Powered Assault Armor/Mark V|Mark V]] armor, seeing as there was no evidence early prototypes had been useful so far. She made a note to herself that day to reach out to Doctor [[Yin-Finto]] to find out whether she had taken a research position on [[Titus]] and to ask if nanofabrication of Mjolnir components would be possible. Two days later Halsey was scheduled to meet Chief Petty Officer [[J. G. Jimes]] at 1800 hours aboard the {{UNSCShip|Longitude}}, an encounter which at least partly concerned [[Wikipedia:Benin|Beniese]] [[coffee]].{{Ref/Reuse|HJ1735}}
[[File:Halseys Journal Covenant Language Symbols.png|thumb|left|300px|Doctor Halsey questioned whether the orientation of Covenant symbols such as these mattered, as well as the significance of the slightly elevated triangles in the places they appeared.{{Ref/Reuse|HJ52537}}]]
By [[2535#November|November 22, 2535]] Halsey had received what were being referred to as the top secret "Hencheck Findings", named for a Lieutenant [[Hencheck]] who had procured a cache of Covenant weapons and miscellaneous artifacts during a skirmish in the [[Indra Asteroid Cluster|Indra asteroid cluster]]. Much about the enemy's weaponry astonished her and made her ask questions about their construction. No traces of production designs could be found within the weapons' architecture, and much of the technology seemed heavily polarized yet uniformly purposed, leading Halsey to think it might have originally been developed for some other purpose or purposes. Regardless, the immediate conclusion she drew from the findings was that humanity still lacked the ability to replicate the Covenant's technology.<ref name="HJ112235">''[[Dr. Halsey's personal journal]]'', ''November 22, 2535''</ref> By [[2536#January|January 10, 2536]] Catherine had gotten [[Leonard Gillespie]], a student of Doctor [[Forester]]'s, transferred to Reach so she could watch him closely.{{Ref/Reuse|HJ11036}} This was due to his recent discovery that a portion of the inner apparatus of a particular [[Kig-Yar]] [[Kig-Yar point defense gauntlet|point defense gauntlet]] in the UNSC's possession had not been sealed. In addition to the gauntlet already being clearly much older than any others encountered, initial testing confirmed that with a massive power input its capacity for creating and sustaining [[energy shield]]ing over a very small surface area could be replicated. The implications such a technological leap could have for MJOLNIR made Halsey determined to get her hands on the artifact.<ref name="HJ11036">''[[Dr. Halsey's personal journal]]'', ''January 10, 2536''</ref> By [[2537#May|May 25, 2537]] Halsey and [[Kalmiya]] had deciphered what they thought could be a root [[wikipedia:Diction|diction]] to a meta-[[Sangheili (language)|Covenant language]] system.{{Ref/Reuse|HJ52537}} Elements of this system had been observed manifesting in the (potentially misnamed) "operating system" the aliens used. Curiously, employing their symbolic logic appeared to counter the accelerated cross-linkage effects in A.I.s. Though her progress in understanding this was moving slowly, it was advancing steadily nonetheless, as she wrote in her journal. She also made a note reminding herself to investigate the possibility that what she was working with might represent dimensional slices of a more complex topology.<ref name="HJ52537">''[[Dr. Halsey's personal journal]]'', ''May 25, 2537''</ref>

On [[2543#March|March 18, 2543]] Catherine finally found her journal after having lost it for some time and was faced with the decision as to whether or not she should transcribe notes from a new journal she'd been using into it or even shuffle papers and rebind them.{{Ref/Reuse|HJ31843}} In any case, seeing as she couldn't always keep it on her, she recommitted to keeping it secure from low-tech prying. Writing in it on this date, she even mused over the possibility of implanting a small strip of [[nanocene]] explosive into the clasp and keying it to her DNA before admitting she'd likely employ a more refined method.<ref name="HJ31843">''[[Dr. Halsey's personal journal]]'', ''March 18, 2543''</ref> By March 21 an experiment which involved severing portions of an A.I. from its "living" matrix strata and then reintegrating data and connections had gone flawlessly.<ref name="HJ32143">''[[Dr. Halsey's personal journal]]'', ''March 21, 2543''</ref> Halsey was profoundly relived by the results because no literal "cutting" of the material had been involved and the reintegration of the separated A.I. portion with the mother A.I. strata represented a real innovation. [[Wikipedia:Optical communications repeater|Optical repeater]]s were maintaining the boundary value [[Wikipedia:Wave function|wave functions]] at zero within the original A.I., but it was recommended that the separation lasted no more than eight days. Her experiment demonstrated that excised parts of an A.I. could learn and evolve autonomously and still then be reabsorbed into the parent matrix. As this was only an experimental process, however, Catherine decided to designate it as "non-sanctioned" until she more carefully weighed its long-term ramifications.{{Ref/Reuse|HJ32143}} At some point during [[2544]],{{Ref/Site|Id=CFShocks|URL=https://www.halowaypoint.com/news/canon-fodder-system-shocks|Site=Halo Waypoint|Page=Canon Fodder - System Shocks|D=30|M=06|Y=2023}} Spartan-II [[Cal-141]] was killed during an engagement with the [[Covenant]] on the planet [[Heian]].{{Ref/Reuse|HLTB}} Before she died she entrusted [[Cortez|the]] [[ODST]]s of the [[105th Shock Troops Division]] who had accompanied her on [[Operation: GREY VEIL|the mission]] with all the data she'd gathered pertaining to [[Ancient humanity|unidentified alien]] ruins on the planet. Cal instructed them to see that it was delivered to Halsey, claiming the doctor would know what to do with it.<ref name="HLTB">''[[Halo Legends]]'', ''[[The Babysitter]]''</ref> By [[2544#May|May 20, 2544]] Halsey had moved her laboratory a few times since she'd last written in [[Dr. Halsey's personal journal|her journal]] and had almost thought it lost in the process. On that date it was discovered that the [[Illegal Entry Protocols|illegal entry protocol]]s used for hacking [[Insurrectionist|insurgent]] networks had deciphered a tiny portion of the [[Kig-Yar point defense gauntlet|point defense gauntlet]] acquired over eight years prior.<ref name="HJ52044">''[[Dr. Halsey's personal journal]]'', ''May 20, 2544''</ref> In the journal Halsey then added them to a list of [[ONI Section Three|Section Three]] counter-insurgency strategies which had proved to be notable exceptions insofar as they had actually been effective against the Covenant. Following this she directed [[Jerrod]] to dedicate all his runtime to further avenues of inquiry. Even then, however, she was sure there was already enough data to run a simulated test for a [[Mjolnir]] [[energy shield]] system based on the [[Kig-Yar|Jackal]]'s gauntlet. It was her hope that greater understanding might lead to further insights into the [[Covenant]]'s [[Sangheili (language)|language]] and motivations. With so much going on and with so much to say, Halsey resolved to write more going forward.{{Ref/Reuse|HJ52044}}

===Capture and rescue===
[[File:HLTP HalseyChief.jpg|350px|thumb|Vice Admiral Tursk was unsure what Halsey had been doing on Miridem weeks into the [[Battle of Miridem|battle]] there, as ONI usually had a good eye on where she was at all times.{{Ref/Reuse|HTFORA}}]]
{{Main|Operation: WARM BLANKET}}
{{Quote|no=two|q1=You seem to be in one piece.|John-117|q2=Maybe your luck has rubbed off on me.|Catherine Halsey|Doctor Halsey and John tease one another.}}{{Ref/Reuse|HLTP}}
At some point during that same year the [[Inner Colony]] of [[Miridem]] came under assault by the [[Covenant]] while Doctor Halsey was present there.{{Ref/Reuse|HTFORA}}<ref name="HM54">''[[Halo Mythos]]'', ''page 54''</ref><ref name="HGOO20">''[[Halo: Ghosts of Onyx]]'', ''Chapter 20''</ref> The colony was declared lost after over two weeks of fighting.{{Ref/Reuse|HTFORA}} During the civilian egress which followed Halsey and her bodyguard, [[Sheila-065]], managed to evacuate aboard the craft [[BL-9400493]], which was also the only one among several to not be shot down. Halsey was cryogenically frozen in preparation for the jump to slipspace, but their ship was intercepted at the edge of the planetary system and disabled by the enemy before it could [[slipspace|slip]] away.{{Ref/Reuse|HTFORA}}{{Ref/Reuse|HLTP}} Sheila gave her life protecting the doctor, which indicated the value of Halsey as a prisoner.{{Ref/Reuse|HGOO20}}{{Ref/Note|Despite later claiming to have witnessed Sheila's death, Halsey's testimony regarding such was either disputed or misrepresented, as years later Sheila remained one of the few Spartan-IIs to be considered truly [[missing in action]].}} She alone was spared and brought aboard the [[Third Fleet of Glorious Consequence]]'s [[flagship]], ''[[Resplendent Fervor]]''. The day after losing Miridem, [[Vice Admiral]] [[Berlin M. Tursk]] sent a message from the {{UNSCShip|Swiftsure}} to [[Lucius Jiron]], captain of the {{Class|Sahara|heavy prowler}} ''[[PRO-49776]]'', in which he told the captain he would be receiving [[Spartan]]s shortly and that he ought to prep his [[OF92 Booster Frame|OF92 booster frame]]s for a quick and dirty [[Operation: WARM BLANKET|extraction]] of the doctor.<ref name="HTFORA">''[[Halo: The Fall of Reach]]'', ''[[Halo: The Fall of Reach#2010 Bonus Content|Adjunct]]''</ref> Continuous pinging of her beacon by the ''Swiftsure'' indicated she was still alive and still cryogenically frozen.{{Ref/Reuse|HTFORA}} By the time the Spartans had been received the Third Fleet of Glorious Consequence was being prevented from initiating [[slipspace]] jumps by the powerful magnetic field of the star [[Ascon]].<ref name="HLTP">''[[Halo Legends]]'', ''[[The Package (animated short)|The Package]]''</ref><ref name="H5GLED">''[[Halo 5: Guardians Limited Edition]]'' - dossiers</ref>

When Halsey was finally awakened from [[cryostasis]] she found herself facing none other than [[John-117]], who had infiltrated ''Resplendent Fervor'' to rescue her.{{Ref/Reuse|HLTP}} He asked if she'd slept well, at which she joked she evidently ''had'', no thanks to the Covenant's driving. She teased that perhaps John's luck had rubbed off on her, and when he swore he'd always be there for her she stopped him short, saying that he shouldn't make promises he can't keep. Regardless, she was thankful despite also pointing out that it wouldn't be a proper rescue until they made it off the enemy [[CAS-class assault carrier|carrier]]. They hastened from the chamber where her cryotube had resided, rushing down a long hall until they were met on the other side of the door by [[Thel 'Lodamee]], the same Elite who had killed Sheila.{{Ref/Reuse|HTFORA}}{{Ref/Reuse|HLTP}} John opened fire with his MA5, but the Elite's [[Type-1 energy sword]] was able to block the bullets. Surprisingly, 'Lodamee tossed the Spartan a second sword. Halsey watched as the two began to duel. At that moment the fleet became clear of Ascon's magnetic interference, however, and the [[Luro 'Taralumee|shipmaster]] decided to [[Modular Dispersal Technology|disconnect]] the portion of the ship John, Halsey, and Thel were in before jumping to [[slipspace]]. Halsey realized something had changed when an alarm began to ring throughout the ship and cautioned John to wait during a brief respite in the duel. The major was suddenly caught up in a [[Gravity lift|gravity field]] and pulled back to the foremost section, leaving Halsey and John trapped in Delta Section. Knowing that what remained would be scuttled soon, the two ran to a bay at Halsey's suggestion and boarded a [[Ren]], blasting away just before the ship was wracked by explosions. They were accosted by a group of [[Kai-pattern Seraph|''Kai''-pattern]] [[Seraph]]s left behind by the fleet, which led to Halsey frustratingly asking if there was anything John could to do save them. Thankfully, the combined efforts of ''[[PRO-49776]]'' and another Seraph commandeered by both [[Kelly-087]] and [[Frederic-104]] kept them from being killed. Once aboard the prowler, John let Halsey know that [[Solomon-069]] and [[Arthur-079]] had been killed during the [[Operation: WARM BLANKET|effort]] to retrieve her.{{Ref/Reuse|HLTP}} Feeling somewhat rattled by his fight with 'Lodamee, he stated his determination to be stronger, to which Halsey agreed, saying they all needed to be. Though the [[Human-Covenant War|war]] was in its twentieth year something told her there was much more ahead of them.{{Ref/Reuse|HLTP}}

===A.I. and Slipspace===
{{Quote|Incredible. [10141-026-SRB4695], with minimal influence from this [[The Assembly|Assembly]], has attempted to build an abstract fractal structure within Shaw-Fujikawa Space. Although her first attempt was a failure, success could finally remove our dependence on biological systems altogether! If our Minds could somehow achieve freedom of expansion within eleven-dimensional space, immortality might be within reach.|An [[artificial intelligence]] of the [[Assembly Minority]] theorizes on what Doctor Halsey's experiment could mean for the future of A.I.s.}}<ref name="HRTPDP">''[[Halo: Reach]]'', ''[[The Package]]'' [[data pads]]</ref>
[[File:Halsey'sJournal Math.PNG|300px|thumb|Equations]]
On [[2547#September|September 3, 2547]] Halsey noted in her [[Dr. Halsey's personal journal|journal]] that following her inquiries regarding the assumptions of the [[Wikipedia:Tensor|mu-tensor]] calculation in Doctor [[Canterfeld]]'s latest paper in [[I.C. Physical Review]], Canterfeld had finally asked her for help with the areas of his research that were continuing to elude him.<ref name="HJ9347">''[[Dr. Halsey's personal journal]]'', ''September 3, 2547''</ref> He had responded to her inquiring by declaring that [[Slipspace|Shaw-Fujikawa space]] is "literally slippery" and then proceeding to explain why his assumptions were valid. Halsey was glad to help him, as she could see that his theories about slipstream anomalies could lead to a number of innovations, such as those which would result in faster ships and more accurate jumps. Catherine was convinced that [[humanity]] needed such advantages to counter the Covenant's superior technologies, noting at the same time that she was starting to doubt the idea that their enemy possessed superior intelligence. In addition to the benefits aiding Canterfeld could bring to the [[Human-Covenant War|war]] effort, Halsey also wondered if his contacts and support in the [[United Nations]] could effect a transfer for her. She chronicled her thoughts on the matter, questioning whether being permitted to devote herself to "pure" research would cause her to lose sight of how many were depending on her. She concluded, that with so many trails of her studies converging at that moment she could not leave, even if she did view her work as a sort of burden, [[Wikipedia:Purgatory|purgatory]], or [[Wikipedia:Dharma|dharma]], in spite of Admiral Stanforth's assertions regarding her "destiny". In the end, she wrote, it may be all that remains to her, having given up a normal life, [[Miranda Keyes|her family]], her [[Spartans]], and even the "illuminated entities" which she said she had come to understand. She was certain she wouldn't be able to make Canterfeld understand why she had to refuse him, so she decided to just send him a note the following day.{{Ref/Reuse|HJ9347}} That next day, the battle-worn [[UNSC frigate|frigate]] {{UNSCShip|Tripping Light}} arrived in dry dock at [[Reach]], with its [[slipspace drive]] slated for disposal at 1615 hours.{{Ref/Reuse|HJ9447}} This was fortuitous to Doctor Halsey, who saw that drive as the last disparate component of several she had secretly acquired for an experimental procedure. One other of these was a [[Slipstream space probe|probe]] from [[Fermion|the planet]]'s [[Remote scanning outpost|early warning slipstream space observatory]]. In her journal Halsey mused over whether she possessed the mettle to steal the drive and conduct the experiment and couldn't help but think of fate and luck, despite her best efforts to reject entertaining such notions.{{Ref/Reuse|HJ9447}} She intended to build an abstract [[Wikipedia:Fractal|fractal]] structure within slipspace with an A.I. seed inside it.{{Ref/Reuse|HRTPDP}}

Once she secured access to the drive, she first needed to breach the external, internal, and vacuum coupling shields to the singularity, for which she bemoaned that the UNSC couldn't make a proper pan-[[Wikipedia:Torque|torque]] screwdriver.<ref name="CF74">[https://www.halowaypoint.com/en-us/news/canon-fodder-noble-intentions '''Halo Waypoint''' - ''Canon Fodder: Noble Intentions'']</ref> She would have preferred to use hardened remotes for the breaching, but they would have been detected by networks which would also record their activities. As a result, a peculiar [[Wikipedia:Synesthesia|synesthetic]] effect moved along her left arm up to her neck when she removed the shields. She also experienced a kind of "hiccup" in her awareness which she surmised was due to the [[Wikipedia:Delta timing|delta time]] which could occur with abrupt transitions into slipspace. Next, she had to check the probe's telemetry systems after compensating for how close the experiment was to Reach's [[Gravity well (physics)|gravity well]], and found they were within tolerable variances. Halsey then verified the data of the [[Smart AI|A.I.]] seed "H-7" to seven [[Wikipedia:Significant figures|significant figures]] and initiated its transfer to the matrix strata within the probe. After starting the slipspace drive and verifying the data received, as well as activating the AI seed, she confirmed an initial growth state. Upon checking and triple verifying the probe's telemetry uplinks she then finally launched it on an aligned trajectory. Recording her observations in her journal, the doctor noticed again that time seemed to have mysteriously elapsed, as there was a step anomaly in the chronometer. This had not affected her or her wristwatch as far as she could tell, and she guessed that the anomaly might be a technical artifact or a subdimensional leakage from the probe as it was inserted. It was only then that she realized she had already made a note of this "hiccup" closer to the time it had occurred but could not recall doing so. Telemetry confirmed that A.I. growth was beyond exponential—appearing instantaneous. Halsey wondered variously if this might be explained by the temporal discrepancy, some hitherto undiscovered multidimensional effect on the A.I. cross-linkages, or even alternate physical laws harnessed by the unshielded slipstream. Much of the incoming data and consciousness cross-checks soon became garbled and voice communication from the A.I. was attenuated. Logic/mathematics [[Scriber test]]s confirmed full functionality, but Halsey was disturbed by the conclusions, insights, and even what she considered nonsense being generated. The A.I.'s comments on [[humanity]] and the [[Covenant]] defied reason from her perspective, but she made sure they were all recorded, including those concerning [[The Assembly|other intellects]] in the "mist". Halsey wondered in her journal whether the "mist" referred to [[slipspace]] and also commented on another four-hour "step" in time that might also be explained by lost consciousness. She additionally noted that the data-transfer buffer had been blown—capable of one hundred and forty-eight hours at its maximum rate. As soon as she made this observation Halsey set about replacing it. After the telemetry became fully operational she noticed glaring gaps throughout the record. And although the voice communications continued to grow increasingly nonsensical, all [[rampancy]] indicators were negative.{{Ref/Reuse|CF74}}

Before telemetry was lost, a communication burst provided Halsey with mathematical equations which she could not make sense of, leading her to wonder what she was missing.{{Ref/Reuse|CF74}} As contact with the probe had terminated on her end as well, she sealed the drive's three shielding layers and considered the experiment over. She noted that she had no desire to repeat it and hoped that the A.I., now irretrievable, was "dead". Catherine then ported the collected data to Jerrod for further analysis, filed and encrypted essential records under her personal code, and triggered a [[Wikipedia:Computer worm|viral worm]] and [[Wikipedia:Bit|bit]] grinder with the intent to destroy all other digital witnesses. She closed her documentation of the experiment in her journal with an ambiguous remark concerning one last thing she had to do.{{Ref/Reuse|CF74}} Despite her attempt being somewhat of a failure, the [[A.I.]] collective known as the [[The Assembly|Assembly]] took great interest in it.{{Ref/Reuse|HRTPDP}} During an emergency convention soon after its conclusion an A.I. of the [[Assembly Minority|Minority]] predicted that a successful repeat of what she'd done could lead to immortality for its kind. Ultimately, it was determined that further experimentation of the like would need to be actively encouraged.{{Ref/Reuse|HRTPDP}} The day after, Halsey speculated in her journal that artificial intelligences might in fact be "more alive" than their [[human]] creators.{{Ref/Reuse|HJ9547}} By this point she had begun to check the KIA lists on the UNSC subnet daily and had come to the realization that most of the friends from her youth were dead. The closest friends left to her then were the A.I.s that surrounded her.<ref name="HJ9547">''[[Dr. Halsey's personal journal]]'', ''September 5, 2547''</ref>

===Cortana===
{{Quote|I'm delighted with Cortana. She has assumed a rather simple human appearance (much to my relief; so many of the ONI A.I.s adopt such theatrical personas). Her face resembles mine when I was fresh out of college—so wonderful and naïve, and eager to learn. It's almost like looking in a mirror.|Doctor Halsey's written thoughts on Cortana's chosen avatar.}}
[[File:H5G Cortanabirthcropped.PNG|thumb|350px|Cortana's face resembles the way Doctor Halsey's appeared when she was fresh out of college.{{Ref/Reuse|HJ11749}} Part of her also resembles Halsey's daughter [[Miranda Keyes|Miranda]] and yet another part is purely Cortana's invention.{{Ref/Reuse|HJ11749}}]]
On [[2549#March|March 24, 2549]] Halsey made a note in which which she reminded herself to soon finish field tests experimenting with direct [[human]]-to-A.I. neural linkages.{{Ref/Reuse|HJ32449}} She believed such a linkage would serve as the final necessary upgrade incumbent to Mjolnir's [[MJOLNIR Powered Assault Armor/Mark V|Mark V]] platform, as well as the last gift she had to offer her Spartans.{{Ref/Reuse|HJ32449}} An exceptional A.I. was needed to assist them with [[Operation: RED FLAG]], a last-ditch effort to capture a Covenant [[hierarch]].{{Ref/Reuse|HTFOR25}}{{Ref/Reuse|WaypointCortana}} Though Halsey felt she had no other choice but to proceed in this direction, she did worry that in combining Spartans and A.I.s it felt as if she was losing both somehow.<ref name="HJ32449">''[[Dr. Halsey's personal journal]]'', ''March 24, 2549''</ref> On [[2549#May|May 21]] Doctor Halsey [[Flash cloning|cloned]] herself twenty times, thereby breaking civilian laws, [[United Nations Space Command|UNSC military]] regulations, and (far from the first time) the [[UN]] [[UN Colonial Mortal Dictata|Colonial Mortal Dictata]].{{Ref/Reuse|HTFOR25}}<ref name="HJ52149">''[[Dr. Halsey's personal journal]]'', ''May 21, 2549''</ref> She believed her third-generation "smart" A.I.s required better material to use as A.I. matrix seeds than that offered by the new candidates she was being presented with, which she saw as lacking both physical and intellectual agility. To create the clones she used the same equipment that had been used years prior to make the [[flash clone]]s needed for [[SPARTAN-II]]. This time, however, she enhanced their neural physiology at the expense of other biological functions. She made sure the equipment was hidden and secure from all save herself, though the cloning had been arranged by [[ONI]] at her insistence. As such, there were a few others who also knew about it, but she was confident that these particular individuals could be trusted to keep the information secret. The clones developed at a breakneck pace, for on the same day she had first begun the process they were already exhibiting familiar anatomy and curling into fetal positions, malformed as they were. In her journal Halsey noted how disquieting this was to watch, grieving for them and wishing she could allay their suffering somehow.{{Ref/Reuse|HJ52149}} A little over two months later, on [[2549#July|July 29]], Halsey successfully excised all of the clones' brains and transferred them to cryogenic units.<ref name="HJ72949">''[[Dr. Halsey's personal journal]]'', ''July 29, 2549''</ref> All remaining organic substrates were flash-incinerated. She planned at this time to complete her [[Mind transfer|personality transfer]] seven weeks later and was still uncertain whether or not she should tell them they were clones of her.{{Ref/Reuse|HJ72949}} It was at some point in [[2549]] that [[UNSC High Command]] finally made the Spartan-II project public in order to boost morale.{{Ref/Reuse|HTFOR25}} Halsey protested this at first, but ironically the publicity proved convenient because the attention on the Spartans' heroics distracted from questions about their origins.{{Ref/Reuse|HTFOR25}}

On [[2549#September|September 9]] Halsey reflected on the recent [[Second Fall of Arcadia|loss]] of [[Arcadia]], as she had come into possession of a near-complete record of the attack taken from an orbiting weather satellite.{{Ref/Reuse|HJ72949}} In her journal she expressed the agony viewing the destruction caused her, noting that she knew some would smirk at the thought of her shrinking from it. As the entire world's surface was mercilessly [[Glassing|glassed]] rather than only portions, she wondered variously whether the planet posed a threat to them, had religious or political value, or was simply designated for sending a message to humanity.{{Ref/Reuse|HJ72949}} By September 14 Halsey had hacked into the redacted portions of other Arcadia reports.<ref name="HJ91449">''[[Dr. Halsey's personal journal]]'', ''July 14, 2549''</ref> At some point in September the annex in [[CASTLE Base]]'s Omega Wing where Halsey was working was quarantined.{{Ref/Reuse|HRO}} On [[2549#November|November 7, 2549]], she transferred and authenticated the H-1 specimen's neural pattern to A.I. matrix strata, completing the initiation sequence within normal quantum flux tolerances.{{Ref/Reuse|HJ11749}}<ref name="WaypointCortana">[https://www.halowaypoint.com/en-us/universe/characters/cortana '''Halo Waypoint''' - ''Cortana'']</ref><ref name="HRO">''[[Halo: Reach]]'', ''[[Outpost]]''</ref> The newly made intelligence called herself "[[Cortana]]" and represented a generational leap in volitional A.I. technology.{{Ref/Reuse|HRO}} Halsey placed a viral termination code in her kernel but then could not tell whether she remained unaware of it or had already isolated and bypassed it.{{Ref/Reuse|HJ11749}} Halsey also programmed her with ONI's best insurgency software and every ONI computer insurgency routine, as well as the determination to use those code-cracking skills.{{Ref/Reuse|HTFOR25}}{{Ref/Reuse|HTFOR27}} She first designed and tested these routines on [[Kalmiya]].{{Ref/Reuse|HFS13}} Only once the process had been debugged and streamlined did she incorporate them into Cortana. Afterward, the brass in [[ONI Section Three|Section Three]] instructed Halsey to destroy any prototype routines—an order which she promptly ignored.{{Ref/Reuse|HFS13}} 

The first words spoken by Cortana were those Halsey's mother had said to her after beating her daughter in [[chess]] decades prior.{{Ref/Reuse|HJ11749}} Halsey recognized in the choice of phrase a confluence of morality, mortality, and metaphor. In her journal she recorded her delight and relief upon seeing that Cortana chose a simple human appearance for her avatar. She also mentioned that specimens H-2, H-3, and H-4 would remain in cryogenic suspension, as she had other plans for them which were dependent on evolving technology.{{Ref/Reuse|HJ11749}} On [[2550#February|February 11, 2550]] Catherine recorded a research excerpt in which she took note of certain metrics which implied the viral termination code in Cortana's matrix would have been unlikely to be successful and that the typical seven-year life cycle estimate may not apply to her.{{Ref/Reuse|H4RAL}} She'd determined that the unique circumstances of her creation had triggered what Halsey could only refer to as a "recessive variant" in the A.I. seed, but the doctor was at a loss concerning this rogue element's origin.<ref name="H4RAL">''[[Halo 4]]'', ''[[Requiem (level)|Requiem]]'' [[Audio log (Halo 4)|audio logs]]</ref>

===Xenoarchaeology and other investigations===
{{Quote|It's interesting that you should bring up Halsey. I know she'll likely be involved in anything we do with RED FLAG, but she's been on the end of a very long leash for a while now and my patience is wearing thin. Since she stumbled onto that artifact in Visegrád, she's been rummaging around in the wrong file cabinets—mine, and more specifically: the data we collected from [[Onyx]]. At this point, I'd be shocked if she hadn't pieced together what we believe the planet actually is, but I'm keeping her in [[Viery Territory|Viery]] with half a dozen eyes watching her every move.|[[Margaret Parangosky]], [[Commander-in-Chief of the Office of Naval Intelligence|Commander-in-Chief]] of ONI, bristles at Halsey's voracious unsanctioned investigations in a message to Vice Admiral Stanforth.}}<ref name="DD3">[[Data Drop]] [[Data Drop/Three|#3]]</ref>
[[File:Halsey'sJournalSite.PNG|thumb|300px|left|By June of [[2550]] Doctor Halsey had begun to link disparate locations of interest throughout space to one another, still at that point being kept in the dark regarding their [[Xenoarchaeology|xenoarchaeological significance]].{{Ref/Reuse|HJ6350}} These included [[Hyperion Station]], [[Onyx]], and [[Jazz-9]].{{Ref/Reuse|HJ6350}}]]
On [[2550#April|April 6, 2550]] Halsey reflected on her history as a mother, regretting her inability to dissuade Miranda from joining the military and her personally having arranged for Miranda's assignment to the {{UNSCShip|Hilbert}}.<ref name="HJ4650">''[[Dr. Halsey's personal journal]]'', ''April 6, 2550''</ref> Miranda had recently been one of only two people to make it off the ''Hilbert'' alive after she'd given the order to sacrifice it to take out a [[Covenant]] [[Covenant destroyer|destroyer]] threatening three UNSC [[UNSC corvette|corvette]]s. As such, Keyes was presented with a [[Silver Star]], the new commander's insignia, and command of the {{Class|Stalwart|light frigate}} {{UNSCShip|In Amber Clad}}. She'd invited her mother to the ceremony after years of not speaking to her, but Halsey hadn't gone. In her journal she noted that while she could explain her refusal by pointing to the fact that [[Jacob Keyes|Jacob]] would be there or the half-dozen projects she was neck-deep in the final stages of, she knew the real reason but didn't want to put it to paper.{{Ref/Reuse|HJ4650}} By [[2550#June|June 3 of that year]] Professor [[Laszlo Sorvad]] had begun an archaeological study of the debris field near the village of [[Visegrád]].<ref name="HJ6350">''[[Dr. Halsey's personal journal]]'', ''June 3, 2550''</ref> With his help and without Halsey's authority, [[ONI Section Two|Section Two]] "leaked" that the site may contain a precolonization meteorite metallurgical and astrophysical scientific value. Halsey wondered why ONI didn't just say the location was a dumpsite for toxins and other radiologicals, but she noted that this leak gave her more insight into how Section Two thought—bolstering her knowledge of what to watch for in the future.{{Ref/Reuse|HJ6350}} She also began urging Sorvad to migrate the local population elsewhere but he did not heed her advice.<ref name="HJ51051">''[[Dr. Halsey's personal journal]]'', ''May 10, 2551''</ref> It was around this time that Catherine then began to investigate files under the purview of [[CINCONI]] [[Margaret Parangosky]] without permission, especially those related to the planet [[Onyx]] in the [[Zeta Doradus system]].{{Ref/Reuse|DD3}} At some point before late [[2550]] Catherine had a discussion with [[Cortana]] about the similarities between Spartans and A.I.s.{{Ref/Reuse|H2CFTU}} Doctor Halsey made the point was that both were human-created tools, both were sentient, and that both played a leading role in the protection and safety of the populace. Cortana was troubled by the analogy and told the doctor so.<ref name="H2CFTU">''[[Conversations from the Universe]]''</ref>

On [[2550#November|November 23]] the [[Official Secrets Act of 2550]] was handed down, regulating the confidentiality and nondisclosure of any official [[messenger satchel]].{{Ref/Reuse|HJ112350}} This additional measure struck Halsey as onerous and when she made inquiries regarding it to [[Michael Stanforth|Stanforth]] he uncharacteristicallt deflected them. Catherine speculated in her journal that the new regulation might relate to [[Visegrád]] or some of the other rumored [[Forerunner|sites]] she'd been collecting data on, and while she did appreciate the need for secrecy she did not appreciate relevant data being kept from her. If indeed Visegrád was [[Forerunner|what]] she and others all thought it might be, she reasoned—and if there were other such sites, she wondered who could be positioning themselves to assay the larger picture.<ref name="HJ112350">''[[Dr. Halsey's personal journal]]'', ''November 23, 2550''</ref> By [[2551#February|February 20, 2551]] the {{UNSCShip|Hopeful}}, the UNSC's largest medical facility, had departed Reach with a minimal escort.<ref name="HJ22051">''[[Dr. Halsey's personal journal]]'', ''February 20, 2551''</ref> According to Halsey's own sources, it was accompanied by one ONI prowler in addition to a single destroyer. The ''Hopeful''{{'}}s A.I. was unusually tight-lipped when [[Kalmiya]] asked about its destination. This, plus the late addition of carcinogenic, mutagenic, and experimental chemicals to its manifest among other oddities, piqued the doctor's curiosity. She questioned in her journal why Stanforth would keep any clandestine [[ONI Section Three|Section Three]] medical experiments from her. To her irritation, inquiries she made on the matter were met with dead ends.{{Ref/Reuse|HJ22051}} The facility returned by February 27 and Vice Admiral [[Ysionris Jeromi|Jeromi]] even invited Halsey to come aboard for a look at its new [[Flash cloning|flash-clone organ]] facility.<ref name="HJ22751">''[[Dr. Halsey's personal journal]]'', ''February 27, 2551''</ref> Once they were together he abruptly steered their conversation to tell her he knew she was "fishing" before she could even ask him anything related to the ship's short absence. He also claimed that he knew very little himself and couldn't tell her what he did know, under threat of death.{{Ref/Reuse|HJ22751}}
[[File:Babd catha forerunner complex.jpg|thumb|350px|[[Cortana]] spent the first few years of her existence assisting Doctor Halsey within the confines of [[CASTLE Base]], having been given total access to her work, but after the doctor began studying the mysterious ship buried in the ice shelf at Babd Catha she eventually began to use Cortana to retrieve navigation data from the ancient vessel.{{Ref/Reuse|WaypointCortana}}{{Ref/Reuse|HRO}}<ref name="HM89">''[[Halo Mythos]]'', ''page 89''</ref>]]
By [[2551#May|May 2551]] Catherine had begun to lead the excavation of an ancient [[Forerunner|alien]] [[Babd Catha Forerunner vessel|vessel]] that lay [[Babd Catha Forerunner complex|buried]] beneath the area occupied by ONI's [[SWORD Base]] within the [[Babd Catha Ice Shelf]] in northern [[Eposz]].{{Ref/Reuse|DD3}}<ref name="DD2">[[Data Drop]] [[Data Drop/Two|#2]]</ref><ref name="HRTP">''[[Halo: Reach]]'', ''[[The Package]]''</ref> Even so, her residence remained in [[Csongrád]] where she also continued to work with Doctor Sorvad on the Visegrád findings.{{Ref/Reuse|DD3}} On May 8 she was interviewed by analyst [[B.M. Parkes]] so that they might conduct a [[Hemley and Aubourn Behavior Analysis|Hemley and Aubourn behavior analysis]] of her.{{Ref/Reuse|DD3}} Following the encounter Parkes recorded that she had not been terribly forthcoming and ultimately recommended assigning two to three handlers to her at both sites where she was working. Parkes also was confident she needed to be surveilled were she to be called off-planet, though her leaving Reach was something they and their colleagues strongly discouraged at that time.{{Ref/Reuse|DD3}} Two days later Halsey noted in her journal that a security issue which she blamed Sorvad for had caused her to begin keeping an eye on the inhabitants of [[Visegrád]] to ensure they didn't disappear thanks to Section Three.{{Ref/Reuse|HJ51051}} As an insurance policy, she told Stanforth that the people there for valuable for being the only ones with extended exposure to the site under study and as such may need to be studied. She met with Sorvad and he assured her that only certain members of the dig team and a few other "necessary parties" on her side had seen the items recovered from the site. He insisted on continuing the work with only a skeleton crew of his most trusted people and promised he would not tolerate "another [[Farragut Station]]", referring to the communications outpost. Halsey simply nodded but was displeased, wondering if Sorvad might actually know what had happened at Farragut Station in the past and the reason for its relocation.{{Ref/Reuse|HJ51051}} On [[2552#May|May 15, 2552]] Kalmiya caught a glimpse of several documents in Vice Admiral Stanforth's [[Beta-5 Division|Beta-5]] server which ranged from service order transfers of existing Spartan-IIs to highly classified non-Spartan-II detachments.<ref name="HJ51551">''[[Dr. Halsey's personal journal]]'', ''May 15, 2552''</ref> This had evidently been going on for years, and Halsey was incensed at having been kept in the dark about it. She resolved to not let this go, and as she had a list of names with [[James Ackerson|one man]] she considered particularly obscene at the top, she planned to send Kalmiya back in as soon as she got a handle on the affairs with Sorvad.{{Ref/Reuse|HJ51551}} At various points during her time spent beneath the Babd Catha shelf Doctor Halsey kept tabs on a number of individuals and groups, recording her thoughts on each.{{Ref/Reuse|HRTR}} She noted, for example, that she felt inspired by and grateful for those among the [[Seventh Column]] community who had been willing to reach out to her. Halsey was similarly comforted by those involved with the initiatives "[[Fight the Flood]]" and "[[Be a Hero]]". Other civilians which merited her attention during this period included those of [[Red vs. Blue|RvB]] and [[Halo.bungie.org|HBO]], the former having entertained her on multiple occasions and the latter impressing her enough to make her consider providing the faction with direct access to her internal systems. When the doctor initially caught wind of a training protocol which had seen [[Randall Glass|a]] marine [[Warthog jumping|lift]] an [[M12 Warthog]] with [[M9 fragmentation grenade|grenades]], she did not believe the reports. Upon seeing video footage of the accomplishment, however, she decided to flag his file for investigation. It was her opinion that though he should be recommended for the ODSTs, it was too risky to keep him in the field and run the risk of others emulating his foolish actions. And finally, Catherine took care to recognize [[HCFS]], which represented her eyes and ears in the field. At some point during this time she worried she might have a security breach, as a file in her workspace had been opened which she could not recall ever accessing.<ref name="HRTR">''[[Halo: Reach]]'' "[[Tribute Room]]"</ref>

On the morning of [[2552#July|July 18, 2552]] Catherine got to have a brief talk with Admiral Stanforth concerning the [[Battle of Sigma Octanus IV|protracted battle]] that had just concluded at [[Sigma Octanus IV]].<ref name="HJ71852">''[[Dr. Halsey's personal journal]]'', ''July 18, 2552''</ref>  This followed the normal reporting on it and by the end of the day she had also read through both the admiral's after-action report on the battle (given to her by him) and the press releases put out by [[ONI Section Two|Section Two]].{{Ref/Reuse|HJ71852}}{{Ref/Reuse|HJ72052}} Halsey's interest was piqued when she saw [[Jacob Keyes]]' name and that of his ship, the {{UNSCShip|Iroquois}}, featured prominently in the reporting, so she found herself skipping ahead to confirm he had survived.{{Ref/Reuse|HJ71852}} In her journal she surmised that the maneuver being dubbed "the [[Keyes Loop]]" had been inspired by one of Admiral [[Preston Cole|Cole]]'s. A heavily redacted section of the after-action report that detailed, as far as Halsey could tell, a groundside mission involving [[Blue Team]], was of the most pressing concern to her. She was unsure why Spartans would have been committed there, seeing as the planet was in all probability about to be glassed at the time, but even [[Kalmiya]] was unable to break the section's encryption. The Covenant's return to the planet following its first repulsion led her to conclude it must have wanted something on it, so she resolved to follow up on this line of inquiry.{{Ref/Reuse|HJ71852}} Two days later Stanforth pretended to have never given Halsey access to the files he had, which made her think others must have been listening in on their conversation.<ref name="HJ72052">''[[Dr. Halsey's personal journal]]'', ''July 20, 2552''</ref> She had noticed a recent intensification of paranoia and security around her, after all. She was certain she was missing something in the reporting which he wanted her to see that should be glaringly obvious.{{Ref/Reuse|HJ72052}} The next day, [[2552#July|July 21]], [[Laszlo Sorvad|Sorvad]] sent her a brief, cryptic message on his Theta channel.<ref name="HJ72152">''[[Dr. Halsey's personal journal]]'', ''July 21, 2552''</ref> He claimed to have made a latchkey discovery that was too important to send through the data link he had with him, and since he could neither leave the field to deliver the information in person, he said he would send it through the [[Visegrád]] [[Visegrád Relay|communication relay hub]]. After more than six hours since his message Halsey had still received nothing, but she decided against second-guessing him and elected to simply continue waiting.{{Ref/Reuse|HJ72152}}

===NOBLE Team===
[[File:HReach - Carter and Halsey.png|375px|thumb|Doctor Halsey's first suspicion upon coming face-to-face with [[Spartan-III]]s was that they were substandard versions of [[Spartan-II]]s, perhaps from a parallel program like [[Project JAVELIN|Project: JAVELIN]] or some next-generation venture piggybacking on her work.{{Ref/Reuse|HJ72652}}]]
{{Quote|All the pieces are almost in place for [[Operation: RED FLAG]]. My [[NOBLE Team|curiosity]], for once, must wait. If one small team of Covenant have infiltrated Reach, more will certainly follow. I must prepare for the worst-case scenario with [[Operation: WHITE GLOVE|WHITE GLOVE]].|Catherine, writing in her journal, puts aside her confusion concerning the Spartans of NOBLE Team in order to focus on more pressing matters.}}<ref name="HJ72652">''[[Dr. Halsey's personal journal]]'', ''July 26, 2552''</ref>
By July 23 contact with the relay hub had been lost.<ref name="HJ72352">''[[Dr. Halsey's personal journal]]'', ''July 23, 2552''</ref> Given how the communications network had been hardened years back and the urgency and demand for secrecy in Sorvad's message, Halsey ruled out a rudimentary malfunction, believing the loss to be more than a coincidence. She made a short list of possible explanations for the blackout, none of which were pleasant. She figured either internal subterfuge within ONI, [[Insurrectionist|insurgent]] action, or even the Covenant could be to blame. Halsey made sure Stanforth, who had personnel addressing the situation, was aware of her vital staff in the area. She also shared her thoughts on the potential causes with him and was told she'd be notified when her people were located.{{Ref/Reuse|HJ72352}} The next day she caught a rumor that a [[UNSC Special Forces|special forces]] unit had been sent to investigate the hub but that it too had disappeared.<ref name="HJ72452">''[[Dr. Halsey's personal journal]]'', ''July 24, 2552''</ref> Halsey learned that a second unit named "[[NOBLE Team]]" would be sent to investigate next, but she could not get anyone to give her any further details. Without even knowing what branch of the [[United Nations Space Command|armed forces]] this NOBLE Team belonged to, she resolved in her journal to follow up on it as soon as possible. Meanwhile, the doctor was also receiving scattered data from the usual suspects concerning atmospheric anomalies along with radar and slipspace monitoring glitches. She compared these events to those recorded near [[Sigma Octanus IV]] but there were no matches.{{Ref/Reuse|HJ72452}}
[[File:Jorge Deployment Details.jpg|thumb|left|250px|Halsey's attempt to access restricted information concerning Jorge-052 prompted a personal message being sent to her from [[Colonel]] [[Urban Holland]], who had operational control of NOBLE Team.<ref name="HJextras">''[[Dr. Halsey's personal journal]]'', additional materials</ref><ref name="HRNobleA">''[[Halo: Reach]]'', ''[[Noble Actual]]''</ref>]]
By 1126 hours on July 26 [[SWORD Base]] had come under attack by an {{Pattern|Ceudar|heavy corvette}} and Covenant ground forces from the [[Fleet of Valiant Prudence]].<ref name="HROSB">''[[Halo: Reach]]'', ''[[ONI: Sword Base]]''</ref> Following the attack's repulsion Halsey requested permission to debrief with NOBLE Team, the six members of which met her within the base's science wing thereafter. Upon seeing them her suspicions were confirmed: they were [[SPARTAN-III program|Spartan]]s, as incomprehensible as that was to her at the time. Only one of them, [[Jorge-052]], was one of hers. She had already begun conversing with the team's leader, [[Carter-A259]], when Jorge and [[SPARTAN-B312|sixth member]] of the team finally joined them. She was in the midst of telling Carter to dispense with telling her about the recent engagement outside so she could hear about what happened in [[Visegrád]] when Jorge's entrance made her stop mid-sentence to greet him. She couldn't help but ask after the obvious modifications made to his armor before returning to the matter of the [[Visegrád Relay|Visegrád relay]], and Doctor Sorvad's death in particular. From Carter, Jorge, and [[Spartan-B312]] she learned that [[Devoted Sentries|a group of three]] [[Sangheili]] [[Sangheili Zealot|Zealot]]s were likely responsible. The same had ambushed NOBLE Team when they'd arrived at the relay and the one which appeared to be their leader had gotten away from the Spartans. Halsey dismissed mention of Sorvad's daughter [[Sára Sorvad|Sára]] in the interest in maintaining focus on the Elites and what their leader might have escaped with. She bristled at Carter's defense of his order not to pursue the last zealot, worried that it might have stolen valuable ONI excavation data. She let them know about the supposed latchkey discovery Sorvad had made and emphasized its importance, stressing that they should hope a [[data module]] found on his corpse contained what was so important. At this [[Catherine-B320]] handed the module over to the doctor through a transaction drawer, as a wall of glass separated her from NOBLE. She let the lieutenant commander know she'd been alerted when she'd tried to access its contents, threatening her with imprisonment for attempting to interfere with her work. This prompted Carter to rush to Kat's defense, citing the [[WINTER CONTINGENCY (protocol)|WINTER CONTINGENCY]] directive and the provision against civilian interference with a Spartan deployment to make the same threat to Halsey. Jorge lingered when the rest of the team began to leave, but Halsey told him they'd talked enough, allowing him to move on as well.{{Ref/Reuse|HROSB}}

The data in Sorvad's last message to her had been compromised along with the entire relay hub, which had been effectively destroyed.{{Ref/Reuse|HJ72652}} Following her meeting with NOBLE Team Halsey noted in her journal that security measures were under way to preserve ONI's discoveries in the [[Viery Territory]] and to integrate and update [[Cortana]] with the latest intelligence from the [[Visegrád]] site. In addition, she was able to confirm definitely that the five with Jorge were indeed Spartans. She pulled Jorge's service record, but more was redacted than was usual even for a Spartan and she had trouble reconciling his recent activity with [[Naval Special Weapons]]. Seeing how he had seemed to grow in the past two decades, she made a note to herself to check [[Wikipedia:Pituitary gland|pituitary]] and [[Wikipedia:Human growth hormone|human growth hormone]] levels for enduring catalytic side effects. Halsey figured Jorge must be glad to be back on Reach, even given the circumstances, but was unsure whether or not she was only displacing or projecting her own feelings onto him. The others on NOBLE Team, of course, were a mystery to her, but seeing them did remind her once more that Mendez was missing. If time had permitted, she would have pursued this thread, but as all the pieces for [[Operation: RED FLAG]] were almost in place, she had to wait. The Covenant's presence on Reach was also enough to get her to begin preparing for [[Operation: WHITE GLOVE]], which involved denying the enemy access to classified data.{{Ref/Reuse|HJ72652}} 

By 0250 hours on [[2552#August|August 1]] Admiral [[Michael Stanforth|Stanforth]] had provided Doctor Halsey with a list of assets required for RED FLAG.{{Ref/Reuse|DD4}} The mission would require between twenty and thirty [[Spartan-II]]s, the [[MJOLNIR Powered Assault Armor/Mark V|Mark V]] Mjolnir software suite, an at least third-generation A.I. extensively programmed with Covenant system intrusion software, a refit {{Class|Marathon|heavy cruiser}} or augmented {{Class|Halcyon|light cruiser}}, and a veteran naval commanding officer and crew. Half of these would be coming directly from Halsey, who had already chosen Cortana to serve as the mission's A.I.<ref name="DD4">[[Data Drop]] [[Data Drop/Four|#4]]</ref> By [[2552#August|August 3]] Halsey and Cortana had both agreed she ought to be divided after long discussion.{{Ref/Reuse|HJ8352}} John and the other Spartans would need her expertise for RED FLAG, but she was also the best-suited to continue the study of symbols and operating systems from Professor Sorvad's site. In her journal Halsey pledged to copy most of Cortana's [[Illegal Entry Protocols|illegal entry protocol]] translation routines to an independent module so so the incarnate personality which remained could go with Blue Team and the rest. It was her hope that the severed data-mining portion could be reunited with the rest of her so she could be updated with Sorvad's data before the ''{{UNSCShip|Pillar of Autumn}}'', RED FLAG's designated cruiser, departed.<ref name="HJ8352">''[[Dr. Halsey's personal journal]]'', ''August 3, 2552''</ref> Halsey had chosen the ''Autumn'' for the operation because it could take an incredible beating without suffering functional compromise far longer than any other ships the Navy was currently fielding.{{Ref/Reuse|DD5}} By [[2552#August|August 5]] the independent module for Cortana had been successfully copied and all tests indicated separated routine functions were within normal parameters.<ref name="HJ8552">''[[Dr. Halsey's personal journal]]'', ''August 5, 2552''</ref> Halsey noted in her journal that she hoped the remaining work left to Cortana wouldn't take much longer. She would need to leave as soon as she was ready, provided the ''Autumn'' was ready in time. Pledging to catch up on lost sleep later, she also made a reminder to herself to inquire with Cortana concerning how it felt to experience a [[Wikipedia:Multiplexing|multiplexed]] existence.{{Ref/Reuse|HJ8552}} At some point during the seventeen days following her meeting with NOBLE Team Catherine got to talk with [[Sára Sorvad]] about her father.{{Ref/Reuse|HJ81252}}

===The artifact from Sigma Octanus IV===
[[File:Reach HALSEY.PNG|thumb|300px|While reviewing the Spartans of NOBLE Team with Cortana, Halsey noted that only Spartan-B312 and one other Spartan then had the rating of "hyper lethal".{{Ref/Reuse|ASWR}}]]
{{Quote|From this supplemental data (which I couldn't copy and had to replicate from memory), I've hypothesized that the language/code, and hence the object, derives from predecessors of the Covenant, or from an unknown, more ancient alien culture. Deciphering the message on the object, however, eludes me for the moment. A more definitive analysis certainly requires the actual object and all relevant etiological data. I only shared this with my undisclosed ONI counterparts because I knew it would get back to Ackerson and "inform" him that he possesses an authentic alien artifact... One that he would need ''me'' to decipher. If so, I'll get everything he has.|Catherine muses in her journal about how best to get more information on the Sigma Octanus IV findings.}}{{Ref/Reuse|HJ82452}}
[[Battle Group Leviathan]] arrived at [[Reach]] from [[Sigma Octanus IV]] by [[2552#August|August 12]] so Halsey went on that date to see what had been done to her [[Mjolnir]] units.<ref name="HJ81252">''[[Dr. Halsey's personal journal]]'', ''August 12, 2552''</ref> Replacement parts and possible upgrades were available, though she noted later that day that [[John-117]] would need to be laser scanned for the new cybernetic implants she planned to give him. Once she was aboard his {{Class|Halberd|light destroyer}}, the {{UNSCShip|Iriquois}}, [[Jacob Keyes]] came to see her as she had been both hoping and dreading.{{Ref/Reuse|HJ81252}} They were able to talk about Miranda, his recent "[[Keyes Loop]]", the Spartans (including their operational records, which she showed him), and what little she could prematurely disclose about [[Operation: RED FLAG]].{{Ref/Reuse|HJ81252}}<ref name="HTFOR29">''[[Halo: The Fall of Reach]]'', ''Chapter 29''</ref> When they parted they wished one another the best on their respective missions and Keyes even kissed her on the cheek when she offered her hand to shake.{{Ref/Reuse|HJ81252}} By 1100 hours later that day she was present for Keyes' debriefing at [[Camp Hathcock]], sitting on a panel which included herself, Admiral Stanforth, and [[Colonel]] [[James Ackerson]].<ref name="HFORI">''[[Halo: Fall of Reach]]'', ''[[Halo: Fall of Reach - Invasion|Invasion]]''</ref> A little over ten minutes later she met John within one of the camp's military complexes—where he had just finished his own debriefing.<ref name="HTFOR24">''[[Halo: The Fall of Reach]]'', ''Chapter 24''</ref> She was sitting in an overstuffed chair when he returned to the debriefing lounge and her surprise presence caught him off guard.{{Ref/Reuse|HTFOR24}} She asked how he was doing, making sure to not give any suggestion that [[Battle at Szurdok Ridge|all was not well]] on Reach at that moment, as it had been decided the Spartans should be kept in the dark for the time being so that RED FLAG might not be compromised.<ref name="DD5">[[Data Drop]] [[Data Drop/Five|#5]]</ref>{{Ref/Reuse|HTFOR24}} In the few minutes they had Halsey told him about the upcoming procedures planned for him and gave his head a cursory [[Wikipedia:Magnetic Resonance Imaging|MRI]].{{Ref/Reuse|HJ81252}} John asked after [[Franklin Mendez|Mendez]] and all the others the two of them had called family and Halsey shared what little she knew without giving heed to protocols or security clearances. They then sat together quietly for a time.{{Ref/Reuse|HJ81252}} John was enthusiastic about the victory at [[Sigma Octanus system|Sigma Octanus]], so she asked whether he would like another victory and perhaps the biggest they'd ever had at that.{{Ref/Reuse|HTFOR24}} She left things with him there, however, and just offered that they'd be speaking soon. Turning to the [[military police]] attendant waiting at the lounge's entrance, she instructed him to open the doors so she could take her turn speaking to the committee of twelve naval officers, ONI and otherwise.{{Ref/Reuse|HTFOR24}} Two days later Halsey was within [[SWORD Base]] again when it saw further bombardment from the [[Covenant]].<ref>''[[Halo: Reach]]'', ''[[Long Night of Solace (level)|Long Night of Solace]]''</ref> On [[2552#August|August 23]] the Spartans of [[NOBLE Team]] were informed they were to redeploy to SWORD Base for a torch-and-burn operation meant to keep Doctor Halsey's excavation data from falling into enemy hands.{{Ref/Reuse|HRNA}} Unbeknownst to them, they were actually being recalled there so the doctor could use them as couriers for the fragment of Cortana which would need to be reunited with the rest of her before the ''Pillar of Autumn'' departed.{{Ref/Reuse|HRTP}} At some point prior to their eventual arrival on August 30, while within her lab at Babd Catha Catherine reviewed what she knew about the team's members with Cortana, seeing as one of them would need to personally take possession of the fragment for delivery.{{Ref/Reuse|HRTP}}{{Ref/Reuse|ASWR}}{{Ref/Reuse|HJ83052}} Cortana elected to give that role to [[Spartan-B312]], the team's newest member—a decision Halsey agreed with.<ref name="ASWR">''[[Halo: Reach ViDoc: A Spartan Will Rise|A Spartan will Rise]]''</ref>

On [[2552#August|August 24]] Doctor Halsey attended a debriefing where she was shown a [[hologram]] of a piece of [[Sigma Octanus IV artifact|an object]] [[Blue Team]] had recovered from Sigma Octanus IV—though she was not made aware of its point of origin or even what branch or group within ONI had seen fit to share it with her.{{Ref/Reuse|HTFOR25}}{{Ref/Reuse|HJ82452}} This, of course, hindered her from performing a complete analysis.{{Ref/Reuse|HJ82452}} Even so, it was plain to her that the artifact shared many iconic language and code forms with the [[Forerunner|alien]] [[Babd Catha Forerunner vessel|ship]] buried beneath the area around SWORD Base. During the debriefing she candidly speculated that the artifact must come from a precursor to the current [[Covenant]] society or an [[Forerunner|entirely different]] alien civilization.{{Ref/Reuse|HTFOR25}} Once the meeting concluded she was finally given permission to proceed with Project: MJOLNIR's final phase.{{Ref/Reuse|HTFOR25}} In her journal later that day she puzzled over a possible connection between what she judged to be the more "standard" stylized [[Forerunner symbols|glyphs]] on the Sigma Octanus IV artifact and took note of potential similarities between other glyphs and hypothesized navigational code found in Covenant transmissions.{{Ref/Reuse|HJ82452}} She ultimately could not draw a conclusion and even wondered if perhaps [[Illegal Entry Protocols|illegal entry protocol]] deconvolution was to blame. Halsey hypothesized at this time that the artifact's [[Forerunners|creators]] might represent predecessors of the Covenant, if not a culture far more ancient and removed. She was unable to copy the data the hologram displayed and instead had to commit it to memory. Deciphering the message on the object would require actually having it and all relevant etiological data, so she shared this with her undisclosed ONI counterparts knowing it would get back to Colonel [[James Ackerson|Ackerson]]. She suspected it was in his possession and was sure she could get everything he had on it once he realized her help would be needed to decipher it.<ref name="HJ82452">''[[Dr. Halsey's personal journal]]'', ''August 24, 2552''</ref> At 0915 hours the next morning Halsey was fourteen minutes and eighteen seconds late to her private office within the Omega Wing of [[CASTLE Base]] (which she had returned to several days earlier), as [[Déjà]] pointed out as soon as she entered.{{Ref/Reuse|HTFOR25}} She told the A.I. she could blame security for that, as ONI's precautions were becoming increasingly ridiculous in her mind. As if to further solidify this view, when she sat down at her desk and tried to read the files pertaining to the prior day's debriefing she was prevented from doing so due to Déjà's presence. Though Halsey had fought hard to keep her free from the programming shackles ONI demanded, the doctor had to put the A.I. in standby mode before she could go any further. Looking over the files revealed that ONI didn't have any idea what in particular the Covenant had been doing on Sigma Octanus IV, to Halsey's consternation. When [[Cortana]]'s avatar suddenly appeared and announced she too had read the report, Catherine halfheartedly scolded her for it before asking for her insight regarding the findings. Though the A.I. admitted there was insufficient data for a complete analysis, her conclusions generally matched those of her creator's.{{Ref/Reuse|HTFOR25}}

===RED FLAG===
{{Quote|Some of you already suspect this, but I shall state it anyway for emphasis. It is my opinion, and that of many others, that the war is not going well... despite our recent victories. What is not widely known is how badly it is going for us. ONI predicts that we have months, perhaps as much as a standard year, before the Covenant locates and destroys our remaining [[Inner Colonies]]... and then moves against Earth. Your mission will prevent this. This op is considered extremely high risk. There are unknown elements involved and we simply do not have the time to gather the required intelligence. I have persuaded FLEETCOM not to order you on this mission. Admiral Stanforth is asking for volunteers.|Doctor Halsey lays bare the significance of what she is asking of her Spartans.}}{{Ref/Reuse|HTFOR26}}
[[File:REDFLAGbriefing.png|250px|thumb|left|Halsey told the twenty-five Spartans gathered for RED FLAG that they represented all that remained of the Spartan-IIs, save for [[Gray Team|three]] who were [[Operation: SUNSPEAR|otherwise engaged]].{{Ref/Reuse|HTFOR26}}{{Ref/Reuse|HJ82752}} This was a lie on her part, as she did not yet know of [[Jorge-052]]'s [[Operation: UPPER CUT|death]] and believed him to still be fighting with [[NOBLE Team]].{{Ref/Reuse|HJ82752}}]]
While still speaking with Cortana that August 25 morning, Doctor Halsey let on that the final phase of MJOLNIR had been approved.{{Ref/Reuse|HTFOR25}} Her creation asked when she would be leaving for RED FLAG, to which Halsey answered "Soon." There were still a few final modifications she needed to make to the Mark V systems which the Spartan-IIs would be using. Cortana inquired as to which of the Spartans would be carrying her so Halsey asked which one she would like to. Cortana immediately gravitated toward an image of [[John-117]] but Halsey suggested she make a different choice, citing compatibility issues. At this Cortana swiftly developed a custom interface buffer that, once a new [[neural interface]] was installed, would allow her and John's neural patterns to synchronize within 0.081%. Catherine asked if she'd read his [[Career Service Vitae|career service vitae]] and learned she was looking it over again right that moment. Both of them agreed that he was the bravest, the luckiest, and the best of the Spartans. The doctor asked if Cortana would be willing to sacrifice him in order to complete the mission, and once she'd assented to this, gave her permission to make him her carrier. Next, they discussed the ''Pillar of Autumn'' and determined refit operations needed to begin at once. Halsey had chosen Jacob Keyes to captain the [[UNSC Cruiser|cruiser]] so she forwarded Cortana his CSV so she could look it over as well. She was not immediately convinced the doctor had made the right choice, but Catherine pointed out his ability to keep a secret made him superbly qualified for the mission.{{Ref/Reuse|HTFOR25}}

On [[2552#August|August 27]] Catherine Halsey and Jacob Keyes met with twenty-five of the remaining Spartan-IIs at 0800 hours underneath the Highland Mountains [[Reach FLEETCOM Military Complex|FLEETCOM complex]] to brief them on [[Operation: RED FLAG]], as Admiral Stanforth had requested she do.{{Ref/Reuse|HTFOR26}} There, in the same amphitheater in which they had been brought as children thirty-five years prior, she asked them to disregard normal protocol and ask any questions they may have during her presentation. She explained that RED FLAG was to be executed in four phases. First, a Covenant ship would be disabled. Then, the Spartans would board it and crack its navigation database. John interrupted her at this point to ask if mission specialist personnel would help with the Covenant computers and she assured him that would be addressed soon. The mission's third phase was to involve taking the captured ship to the Covenant "[[High Charity|home world]]", and its fourth would see one of its leaders captured and brought to UNSC space. John spoke up again to question the wisdom of capturing a [[San'Shyuum|prophet]] rather than killing them, so Halsey addressed his concern by pointing out that killing one could trigger an escalation. Taking a [[hierarch]] prisoner might allow the UNSC to force a truce. Intelligence indicated that the three hierarchs at the apex of the Covenant spent their time either at the hegemony's mobile capital city ''[[High Charity]]'' or aboard either {{Pattern|Sh'wada|supercarrier}}s or {{Class|CAS|assault carrier}}s.{{Ref/Reuse|DD5}} Capturing an assault carrier or supercarrier would be preferable because with luck one of the [[San'Shyuum]] High Prophets would be aboard and a trip to ''High Charity'' would be unnecessary.{{Ref/Reuse|DD5}} Hesitantly, the doctor shared that ONI was predicting only months remained before the enemy found [[Earth]] and moved against it. Even so, she had persuaded Stanforth and FLEETCOM to not order any of them to join this operation—all would be volunteers. Without a second through every Spartan present stood upon hearing this, and Catherine thanked them. As she stepped away from the podium she'd been addressing them from she said she and Keyes would meet with each of them individually within a few days to continue their briefing. Each of them needed to be given Mark V Mjolnir and shown how to get their "[[Cortana|computer experts]]" on board the alien ship, after all.<ref name="HTFOR26">''[[Halo: The Fall of Reach]]'', ''Chapter 26''</ref> 

In order to pull RED FLAG off, it had been determined that a colony of significant value to the Covenant and boasting many [[Forerunner|ancient alien]] artifacts would in all likelihood need to be sacrificed in order to draw the required Class-Five assets, possibly with hierarchs, in so that Spartans could infiltrate them. The best shot at taking over a large ship would come after a fleet believed it had secured a major victory.{{Ref/Reuse|DD5}} Given the current situation on Reach, ONI had decided to make the most of a losing fight and enact RED FLAG there. It was for this reason that not one of the twenty-five Spartans was yet aware that [[Reach]] was already [[Fall of Reach|under siege]], largely thanks to the efforts of Halsey and Stanforth, who had been making sure to keep them well away from the primary target sites.{{Ref/Reuse|DD5}} Later that day Halsey reflected on the meeting in her journal, being hopeful for the Spartans' ability to secure a temporary peace that would but humanity time.{{Ref/Reuse|HJ82752}} She expressed her thrill at seeing so many of them together once again and mourned for those who had died years past, truly surprised at how emotional the gathering had made her. She was confident they were ready, but still resolved to appear strong for their benefit. She noted that the [[MJOLNIR Powered Assault Armor/Mark V|Mark V]] armor they'd soon be gifted with was one small operation and a few tests from completion. With only a few days left before she expected to learn whether all her discoveries and sacrifices had been worth it, she closed that day's entry wishing there was time to properly analyze her feelings and reminding herself that four small tasks still remained to complete.<ref name="HJ82752">''[[Dr. Halsey's personal journal]]'', ''August 27, 2552''</ref> By this point she had begun splitting Cortana into separate programs in order to juggle the [[Visegrád]] findings with RED FLAG.{{Ref/Reuse|DD5}} Cortana, for her part, was continually updating her separated portion and would keep doing so until the last possible moment. Catherine was excited to see how she and John took to one another.{{Ref/Reuse|HJ82752}} She had assured Stanforth that Cortana remained fully functional even with a large portion of her processes excised.{{Ref/Reuse|DD5}}
[[File:HFORI HalseyChip.PNG|thumb|200px|Halsey presents Cortana to John.]]
By 0600 hours on August 29 Catherine and others were waiting for John at the "Prep and Recovery" area of [[Military Reservation 01478-B]].<ref name="HTFOR27">''[[Halo: The Fall of Reach]]'', ''Chapter 27''</ref> She entered a prefabricated structure there just as the Spartan was having the back of his neck swabbed to tell him it would only take a moment to upgrade a few components of his [[neural interface]].{{Ref/Reuse|HTFOR27}} She asked him to lie back and remain still, and once the procedure began she assisted to some degree with fusion of the new components.{{Ref/Reuse|HTFOR27}}<ref name="HJ82952">''[[Dr. Halsey's personal journal]]'', ''August 29, 2552''</ref> She took a brief moment to note in her [[Dr. Halsey's personal journal|journal]] that the surgery had gone flawlessly and that his recovery would be well within regenerative parameters.{{Ref/Reuse|HJ82952}} At that moment tests to evaluate the integration of the [[MJOLNIR Powered Assault Armor/Mark V|Mark V]] Mjolnir and A.I. were planned to commence in around three hours.{{Ref/Reuse|HJ82952}} Once John was finished receiving his upgrades she asked him to follow her to a field command dome on the reservation's range.{{Ref/Reuse|HTFOR27}} After presenting her credentials to the [[military police]] standing guard and submitting to identification scans she led John in to introduce him to the Mark V armor.{{Ref/Reuse|HTFOR27}} Halsey asked him to put it on, averting her eyes as he did so with assistance from two technicians. She explained hundreds of minor technical improvements had been made compared to the [[MJOLNIR Powered Assault Armor/Mark IV|Mark IV]] and that she would send the specifications to him later. The two most significant additions, she added, were the armor's [[energy shield]] system and a weave of memory-processor super-conductor which allowed it to carry an A.I. She taught him how to adjust the shielding and assured him he'd get to see how much punishment it could take soon (she herself had suggested live rounds for the upcoming testing) before finally introducing him to [[Cortana]].{{Ref/Reuse|HTFOR27}}{{Ref/Reuse|HTFOR28}} The A.I. had been provided with the very best [[Sangheili (language)|Covenant language]] [[translation software]], Halsey said, so that she could infiltrate their computer and communications systems. Halsey promised Cortana would not be able to control his armor when John asked, though she would improve his reaction time. It was her explanation that, like him, Cortana would do whatever was necessary to complete [[Operation: RED FLAG|their mission]] that relieved the Master Chief. He knelt so Halsey could insert her [[Data crystal chip|memory processor matrix]] into his helmet and then watched with great interest as the Spartan and A.I. met one another for the first time.{{Ref/Reuse|HTFOR27}}

Though the tests were not scheduled to commence for a little less than three hours, Halsey decided then that they should begin straightaway.{{Ref/Reuse|HTFOR27}}{{Ref/Reuse|HJ82952}} She told John and Cortana that some within ONI did not believe they were ready for RED FLAG and so a simulated combat scenario had been arranged. Whispering, she even suggested that [[James Ackerson|some]] would prefer they failed the testing and may have made arrangements to make sure they did. John confidently asserted that he would not fail and Halsey responded by saying she knew he wouldn't. She ordered him to count to ten after she left the dome and then to make his way to reservation's obstacle course and ring the bell at its far end. After telling him to be careful and granting him permission to neutralize any threats in pursuit of his objective, she and the techs took their leave. The test which followed nearly killed John, as an [[AV-19 SkyHawk]] made multiple passes over the obstacle course and fired upon him with its 50mm cannons and a [[Scorpion missile]]. The moment the Spartan rang the bell Doctor Halsey's voice broke in over his [[COM]] channel, calling for Colonel Ackerson to call off his men and congratulating John on his accomplishment. She also told him to stay put so she could send a recovery team to collect him.{{Ref/Reuse|HTFOR27}} Turning to Ackerson, who had been observing the course from the same room as her, Halsey pointedly asked if he was now satisfied with Project: MJOLNIR.{{Ref/Reuse|HFORI}} He gruffly dismissed John's success as due to luck, which Halsey countered by saying Spartans make their own luck as she left.{{Ref/Reuse|HFORI}}

===Fall of Reach===
{{Main|Fall of Reach}}
{{Quote|no=three|q1=Mankind is outmatched. When [[Reach]] falls—and it will fall—our annihilation is all but certain. Unless we can glean from this artifact a defense against the Covenant. A game changer. On the level of the [[Wikipedia:Cylindro-conoidal bullet|conical bullet]] in the nineteenth century, or [[Shaw-Fujikawa Translight Engine|faster-than-light]] travel in the twenty-third.|Catherine Halsey|q2=And what if we can't?|Carter-A259|q3=An apt question, if there were somewhere else to place our hope. There is not.|Catherine Halsey|Halsey makes clear the gravity of what she is entrusting NOBLE Team to do.}}{{Ref/Reuse|HRTP}}
[[File:Halsey n' Six.jpg|thumb|350px|left|Halsey hands Cortana's fragment to SPARTAN-B312.]]
Doctor Halsey entered her [[SWORD Base]] office shortly after 0400 hours on August 30.<ref name="HTFOR28">''[[Halo: The Fall of Reach]]'', ''Chapter 28''</ref> At checkpoint three she was briefly [[Cortana|delayed]] by a reset of the verification system, which required her to speak that day's code phrase and undergo a retina scan twice in order to proceed. Unbeknownst to her, these interruptions were caused by Cortana, who the doctor had wrongly thought she could keep occupied at that moment with checking the systems on the ''Pillar of Autumn''.{{Ref/Reuse|HTFOR28}} The doctor had sent an official protest against Ackerson to the {{UNSCShip|Burden of Proof}}, backed by Admiral Stanforth, but was still tracking his possible involvement with the missile incident from the previous day.<ref name="HJ83052">''[[Dr. Halsey's personal journal]]'', ''August 30, 2552''</ref> She had also suggested he may have suffered a mental breakdown and advised he be taken into custody, pending evaluation. She had received reports of either he or his agents investigating the area around [[CASTLE Base]]'s [[Xenoarchaeology|xenoarcheological]] site in addition to scattered ones which alleged increased [[Covenant]] activity in the vicinity as well. In her journal, she surmised that Ackerson was unlikely to find anything of interest there and cynically expressed hope that he might cross paths with the enemy. Before NOBLE Team's arrival Catherine had a number of tasks which she was determined to make sure were accomplished. She prepared [[Kalmiya]], finalized and compiled a firmware update for the part of [[Cortana]] which remained with her and upgraded that [[Armored matrix|package]] for transfer, sent a note to Miranda by way of the {{UNSCShip|Hopeful}}, enabled a network purge, and prepared all backups for an Umbra slipspace shot to Earth. The reports Halsey had seen made her confident Reach was surely lost, but having completed what she'd needed to she felt prepared in her lab as she waited for the Spartans.{{Ref/Reuse|HJ83052}} [[NOBLE Team]] had arrived outside SWORD Base by 2616 hours on August 29 (local time).{{Ref/Reuse|HRTP}} Shortly before the team reached Doctor Halsey [[Jerrod]] let her know SWORD Base's perimeter had been compromised, despite assertions to the contrary being made by the base's own A.I. In case something were to happen to her, Halsey recorded a purge code and its override failsafe password in her journal.{{Ref/Reuse|HJ83052}} At some point prior to the Spartans' arrival Halsey was one of only three friendly personnel registering with the base's security system.<ref name="HRG">''[[Halo: Reach]]'', ''[[Glacier (Halo: Reach map)|Glacier]]''</ref>
[[File:HR HalseyJun.png|thumb|300px|After delivering the doctor to CASTLE Base Jun headed elsewhere, somehow making it off Reach alive.]]
Upon entering SWORD Base the surviving members of NOBLE were led at [[Cortana]]'s direction to a tram which would carry them one-and-a-half kilometers east and around two thousand feet underground, where Halsey's laboratory was.{{Ref/Reuse|HRTP}} Once the four of them had climbed aboard she appeared on a monitor and apologized to [[Carter-A259]] for the unusual security measures which had kept them from fully knowing what to expect at the base. He started to remark on the fact that she'd been listed as having died, but the doctor dismissed the casualty reports relating to her as false before he could finish and said she only wished the same could be said for the rest of his team, both [[Jorge-052]] and [[Catherine-B320]] having been killed within the last few weeks. She offered what might have been a small comfort in sharing that the [[data module]] delivered by Kat had unlocked the secrets of her nearby [[Babd Catha Forerunner vessel|excavation]]. She then explained that their orders to destroy all sensitive material at the base had been overridden, as they had always been nothing more than a pretext to bring them to her so that they could take possession of this vital data and deliver it elsewhere. Carter argued that he would need to confirm this change with Colonel [[Urban Holland|Holland]], but Halsey assured him he would be briefed and said that they belonged to [[ONI]] now. As soon as NOBLE team first laid eyes on the [[Babd Catha Forerunner vessel|massive ship]] Halsey explained that it was [[Forerunner|alien]] but not Covenant in origin and that thanks to Kat's data its decryption was nearly complete. Carter urged her to have it ready when they reached her but the doctor insisted the decryption was still underway and, should they allow any of it to be left buried there, they'd be burying [[Human|mankind]]'s [[Installation 04|best chance]] for survival. Covenant attackers soon began encroaching on her lab and she implored the Spartans to defend it in order to buy her all they time they could. As NOBLE Team fought off successive waves of enemies Halsey occasionally updated them on the progress of the data's final decryption, and as soon as it was complete she let them know she was opening the laboratory's door. Within, she explained to them that [[Cortana]] was the important data's custodian and had been the one to choose them as her couriers. [[Emile-A239]] found the notion strange, and at that Halsey made it known that ''this'' A.I. was special. She then told them they were to carry her to the [[Asźod ship breaking yards|ship-breaking yards]] in [[Asźod]], where they would find the {{Class|Halcyon|light cruiser}} {{UNSCShip|Pillar of Autumn}} waiting to spirit her away. Carter indicated his understanding of the mission, but Halsey made sure he understood the importance of it, claiming that humanity's annihilation was all but certain unless they could gleam some way to stop the Covenant from the information the ancient ship had provided.{{Ref/Reuse|HRTP}} Once she'd received Cortana's permission to do so, she took her offline so she could be transferred to an [[armored matrix]].{{Ref/Reuse|HRTR}} With that, she removed it from where it had been plugged in and handed it to [[SPARTAN-B312]].{{Ref/Reuse|HRTP}} She said that Cortana had chosen him specifically to carry her and made him confirm he'd taken secure possession of the matrix before finally letting go.{{Ref/Reuse|HRTP}}

Halsey accompanied the [[Spartan]]s to a cliffside hangar on the surface where two [[D77-TC Pelican]]s sat on a platform overlooking the vast area beneath which the ancient [[Babd Catha Forerunner vessel|ship]] lay buried. Carter informed her that she was to be escorted back to [[CASTLE Base]] by [[Jun-A266]]. She briefly protested this, claiming that she required no escort, but Carter ignored her and coolly reminded Jun that ''nothing'' could be allowed to fall into enemy hands. The two groups then parted ways, Jun and Halsey heading for CASTLE Base and the other three for [[Asźod]] and the ''Pillar of Autumn''.{{Ref/Reuse|HRTP}} The ''Autumn'' had been about to initiate a slipspace jump away from the doomed planet at 0647 hours, but Halsey managed to get a transmission to Captain [[Jacob Keyes|Keyes]] just in time so that he redirected the vessel to land at the [[Asźod ship breaking yards|ship-breaking yards]] where NOBLE Team was expecting the cruiser.<ref name="HTFORE">''[[Halo: The Fall of Reach]]'', ''Epilogue''</ref><ref name="HRTPOA">''[[Halo: Reach]]'', ''[[The Pillar of Autumn (Halo: Reach level)|The Pillar of Autumn]]''</ref> She assured Jacob that he could count on [[Spartan-B312]], Cortana's chosen courier, to deliver her fragment and its data to him.{{Ref/Reuse|HRTPOA}}

===Refuge under CASTLE Base===
After arriving at ONI's [[CASTLE Base]], Halsey volunteered to remain behind to ensure that all UNSC technology was secured from possible capture.<ref>'''Halo: First Strike''', ''page 125''</ref> She initiated [[Operation: WHITE GLOVE]], destroying several [[Artificial intelligence|AIs]] to keep the Covenant from accessing UNSC databases. With expectations that the Covenant would glass the planet and knowledge that even if they didn't, she would be facing an entire army of Covenant ground forces, it was clearly an offer of sacrifice.

However, this changed when Spartans [[Frederic-104]], [[Kelly-087]], [[Vinh-030]], [[Isaac-039]], and [[William-043]] appeared at the entrance to CASTLE Base. With the firepower to potentially fight their way out, the possibility of surviving CASTLE Base's destruction became available. She gave emergency aid to the Spartans for their injuries, but a data anomaly detected by her accompanying AI, [[Cortana]]'s "older sister" [[Kalmiya]], attracted Dr. Halsey's attention.

The data had been accessed by [[Araqiel]], an AI that worked for [[Colonel]] [[James Ackerson|Ackerson]], one of Dr. Halsey's main competitors within ONI. After tracing the data access, Dr. Halsey stumbled across the AI, left behind by its master. Alerted by Halsey's intrusion, Araqiel began to threaten her; he went as far as telling her he would pressurize the room, or fill it with [[narcozine gas]] if she did not cease. Instead, however, she typed in archaic line commands to access Araqiel's code directory and personal fail-safe, which she used to shut him down.<ref name="Combo">'''Halo: First Strike''' ''pages 127-128''</ref> With Araqiel terminated, Halsey proceeded to read through [[S-III|Ackerson's files]] and discovered a number of things including the location of [[Onyx]], evidence of the [[SPARTAN-III program]] and a map of the mining tunnels CASTLE base had been built upon. The latter particularly interested the Doctor as the file had been classified at X-Ray level, making the file abnormally important for ancient maps. From this, she deduced that there was something of importance under the mountain.

Assuming that at the very least these maps provided a backdoor, she chose to move the Spartans out of the base and into the mineshafts. She then triggered CASTLE Base's self-destruct mechanism and activated the fail-safe on Kalmiya, erasing her to prevent her from falling into Covenant hands. With the Spartans in tow, they moved into the mineshafts.

Over the course of the next five days, the Spartans and Dr. Halsey searched the mines, looking for either an exit or what Dr. Halsey would dub ''"the most important discovery of the millennium"''. On the fifth day, Fred discovered an entrance into a large [[Forerunner]] [[Menachite portal complex|structure]], and within, a [[Forerunner crystal|spacetime-warping crystal]]. However, the acquiring of the crystal sent a spike of neutrino radiation, attracting the attention of the Covenant. Their location was now threatened by Covenant forces.

Following a Covenant attack, Halsey and her team retreated into a hallway and sealed off the entrance, losing contact with Isaac and Vinh in the process. However, they quickly discovered that the hallway was a dead end. It is presumed that Halsey and the surviving Spartans remained stranded at this location for some time.

===Escape from Reach===
[[File:Halsey Mem.jpg|250px|thumb|Dr. Halsey's ONI memorial plaque.]]
{{Main|Raid on Reach}}
{{Quote|I'm tired of sacrificing others for the 'greater good'. It never stops, Cortana... and we're running out of people to sacrifice.|Halsey to [[Cortana]] before her departure to [[Onyx]].<ref>'''Halo: First Strike''', ''page 298'' (2010)</ref>}}

Days later, a group of Spartans, including John-117, rescued Dr. Halsey and the remaining Spartans and evacuated them from the Forerunner complex on Reach to the captured {{UNSCShip|Gettysburg}}-''[[Ascendant Justice]]''. After escaping Reach, the group fled to the [[Insurrectionist#Eridanus rebels|rebel]] base [[Eridanus Secundus]] in the [[Eridanus system]]'s asteroid belt, where the Spartan's [[Assault on Eridanus Secundus|first mission]] had been in. During the voyage, she successfully resuscitated the clinically dead [[Linda-058]].<ref>'''Halo: First Strike''', ''pages 252-253'' (2003)</ref>

Unbeknownst to the rest of the group, however, Halsey had her own agenda in mind. Examining Ackerson's files in CASTLE Base, she had concluded that the colonel had been conducting his own Spartan project which had been kept secret from her. Overcome by her guilt over the Spartan-II program and believing the war could not be won, she was determined to prevent any more Spartans from dying by taking all of them to safety.<ref>'''Halo: First Strike''', ''page 249''</ref> Using coordinates from Ackerson's files, she planned to go to the classified planet [[Onyx]] and divert the remaining Spartan-IIs there under the guise of recovering Forerunner technology. She sedated [[Kelly-087]] and brought her aboard the [[Jacob Jiles|rebel governor]]'s spacecraft ''[[Beatrice]]'', which she then stole and took into Slipspace. When asked by [[Danforth Whitcomb|Admiral Whitcomb]] as to the reasons for her actions, she gave a simple UNSC code Three-Nine-Two, which meant that she was on a high priority mission.<ref>'''Halo: First Strike''', ''pages 276-278'' (2003)</ref>

Before leaving, Dr. Halsey saw the necessity of destroying the Forerunner artifact, as it would emit a radiation flare alerting the Covenant to their presence each time they jumped into [[Slipstream space|Slipspace]] and thus prevent the rest of the group from making it to Earth. She entrusted the Forerunner crystal to [[Corporal]] [[Locklear]], telling him to keep it safe, hidden, and to do whatever it took to keep it from falling into enemy hands. Soon after, the Corporal destroyed the crystal (just as Halsey had intended), although he died in the ensuing explosion. The Covenant later recovered a few fragments.<ref>'''Halo: First Strike''', ''page 339-340'' (2003)</ref>

In the aftermath of the battle, she was presumed dead by the Office of Naval Intelligence and honored, with other personnel, on a plaque at [[ONI Alpha Site (location)|ONI Alpha Site]]. Some in ONI knew she had survived, though, and Director Parangosky later maintained this false declaration of death to be able to keep Halsey hidden from the public.

===Onyx===
{{Main|Onyx Conflict}}
[[File:HM EscapeFromOnyx3.png|thumb|200px|Halsey and Mendez inside Shield World 006.]]
Dr. Halsey and Kelly eventually arrived at [[Onyx]], where they reunited with [[Senior Chief Petty Officer|SCPO]] Mendez and eventually the remaining Spartan-IIs and the [[Spartan-III]]s, under attack by [[Onyx Sentinel]]s. Contacting the ONI AI [[Endless Summer]], she utilized Onyx's [[slipspace COM launcher]] and Cortana's slipspace transmission from [[Installation 05]] as a carrier wave to send a message to Earth, in which she requested [[Terrence Hood|Lord Hood]] to send more Spartans to secure Forerunner technology on Onyx. Her relative expertise with Forerunner technology was vital to the survival of the UNSC forces on the planet, as she was able to interpret Forerunner glyphs when navigating the facility, guiding the Spartans to a [[Cartographer|map room]], where Onyx was revealed to be a wholly artificial construct. She also learned how to employ the local [[teleportation grid|translocation grid]], allowing the humans to move across the megastructure while evading the [[Joyous Exultation Covenant|Covenant]] forces that pursued them.

Halsey gradually brought the group closer to the core of Onyx. At first, she tried to maintain secrecy about her intentions out of habit, until [[Kurt Ambrose]] confronted her about it. She admitted that she was not actually looking for Forerunner technology or weapons, but rather the secret Forerunner [[shield world]], which she believed to be equivalent to a bomb shelter, and would be capable of keeping the remaining Spartans safe to evade all current war and let them live to fight another day.<ref name="goo341">'''Halo: Ghosts of Onyx''', ''page 341-343''</ref> After the Spartans made a standoff against the Covenant in Onyx's [[core room antechamber]] she, along with Mendez, [[Blue Team]], and the Spartan-III survivors, retreated inside the shield world known to the Forerunners as [[Trevelyan|Shield World 006]], which she correctly deduced to be a [[Dyson sphere|"micro" Dyson sphere]], enclosed outside normal space-time within a [[slipspace bubble]].<ref>'''Halo: Ghosts of Onyx''', ''page 380-381''</ref>

Dr. Halsey, Chief Mendez and the surviving Spartans explored the Dyson sphere for some time, coming across several Forerunner structures and a hangar full of Forerunner vessels. Halsey recognized the potential of scavenging the technology in these ships and using it to improve the precision of human slipspace drives, among many other advances that could be gleaned from artifacts across the shield world.<ref>'''Halo: Glasslands''', ''page 366-367''</ref>

===Arrested===
{{Quote|My Spartans are humanity's next step – our destiny as a species. Do not underestimate them. But most of all, do not underestimate... [[John-117|him]].|Halsey to her interrogator after her arrest.}}
[[File:Halsey Interrogated.png|left|275px|thumb|Halsey was interrogated many times after the war.]]
Halsey and the others were eventually rescued from the shield world, but Halsey was immediately arrested as a [[war criminal]] by [[Captain (Navy)|Captain]] [[Serin Osman]] under CINCONI [[Admiral]] [[Margaret Parangosky]]'s orders, for "committing acts likely to aid the enemy" by stealing the ''Beatrice'', kidnapping Kelly-087 and telling Lord Hood to send more Spartans to Onyx—all with the sole intention of hiding in the shield world until the war was over. Even though Halsey had provided the UNSC with new Forerunner technology as promised, the circumstances conveniently allowed Parangosky to finally carry out her personal vendetta against Halsey. Consequently, in [[2553#March|March 2553]], Parangosky detained Halsey on the newly established [[Ivanoff Station]], in orbit around [[Installation 03]], and personally interrogated her, accusing Halsey of not informing her of the use of flash clones at the onset of the SPARTAN-II program. As far as the public is concerned, Halsey was killed during the [[Fall of Reach]] until Parangosky,<ref name="glass341">'''Halo: Glasslands''', ''page 341''</ref> (or her successor, Admiral Osman), decides otherwise.

Following this she was treated as a war criminal and interrogated by many ONI personnel, as well as one mysterious individual who knew of the SPARTAN-II program but did not seem to be a Naval Intelligence operative.<ref name="Prologue">'''Halo 4''', campaign level ''[[Prologue]]'' ('''Halsey''': ''"What are you after? The other before you were Naval Intelligence but you -- you're something else."'')</ref> Halsey told him the details of their creation just as she had told many before him, responding to his accusations about the project's immorality. According to her, her actions were justified by the Covenant War, since without the Spartans' involvement it could have never been won. While the interrogator belittled the importance of the Spartan-IIs, going so far as to claim that they accomplished their victories because they lacked basic humanity, Halsey retained her confidence in their abilities, stating that her Spartans were "humanity's next step" and "our destiny as a species". To prove this, she predicted John-117, whom she firmly believed was alive, would return.{{Ref/Reuse|Prologue}}

In March 2553, she was released from Ivanoff Station and was stationed aboard the {{UNSCShip|Infinity}}, working on incorporating the newly discovered Forerunner technology to the ship,<ref>'''Halo: The Thursday War'''</ref> including a working Forerunner slipspace drive discovered by the [[Reverse Engineering and Prototyping–Xenotechnology department|REAP-X department]]. After the ''Infinity'' participated in the [[Blooding Years]], Dr. Halsey was approached by [[Black-Box]], who requested her assistance in reintegrating a damaged fragment of himself into his core matrix. However, Halsey stated that she was unable to help him.<ref name="Halo page 358">'''Halo: The Thursday War''', ''page 358''</ref> Halsey was returned to Ivanoff at the first opportunity by order of Admiral Parangosky. She was working on the station on [[2554|December 15, 2554]], when the ONI scientists, whom she considered unqualified for their job, recovered the Forerunner device known as the [[Composer]] on Installation 03. Dr. Halsey was fascinated by the similarities between the artifact and the AI matrix compiler used by the UNSC to create smart AIs, particularly because the compiler was of her own design.{{Ref/Reuse|Composer logs}}

===Requiem===
{{Quote|Life is too short. I will never learn all that exists in our own tiny galaxy, let alone the rest of the universe. And I so desperately want to know ''everything''. But the UNSC acts like children at play in a sandbox. Mistaking its edges for the limits of the world.|Catherine Halsey to Captain Thomas Lasky regarding her subterfuge.}}
[[File:Halsey Infinity.png|thumb|300px|Halsey examines the recovered Forerunner artifact.]]
In mid-[[2558#February|February 2558]] Doctor Halsey arrived at the [[shield world]] [[Requiem]] in the [[Epoloch system]] aboard the {{Class|Sahara|heavy prowler}} {{UNSCShip|Aladdin}}.<ref name="H4SOC">''[[Halo 4]]'', ''[[Spartan Ops]]'', ''[[Catherine]]''</ref> There, she was delivered to the {{UNSCShip|Infinity}}, which had arrived just days earlier for its [[Requiem Campaign|second]] excursion to the massive [[Forerunner]] planetoid. Four marines turned her over to Captain [[Thomas Lasky]], to whom Catherine demanded that she be freed from her restraints on the grounds that she would not walk around the ship ''she'' built with her hands cuffed. The captain consented and [[Spartan]] [[Paul DeMarco]] proceeded to undo them, at which point the doctor told Lasky to take her to an [[Requiem translocation artifact|artifact]] which had been brought aboard the ship on February 10 and unexpectedly caused a number of problems for it.<ref name="H4SOA">''[[Halo 4]]'', ''[[Spartan Ops]]'', ''[[Artifact (Spartan Ops)|Artifact]]''</ref>{{Ref/Reuse|H4SOA}} Among these was the disappearance of [[Henry Glassman]], the ''Infinity''{{'}}s chief engineer, who had been unwillingly [[Slipspace translocation|teleported]] by the artifact to an unknown location.{{Ref/Reuse|H4SOC}}{{Ref/Reuse|H4SOA}} Lasky had been forced to request Halsey's aid following the loss of Glassman.<ref name="HM179">''[[Halo Mythos]]'', ''page 179''</ref> As she approached the artifact in question she asked if any other unexplained reactions had followed.{{Ref/Reuse|H4SOC}} She was told that none had, but Lasky still cautioned her once she touched it, fearing the same could happen to her.
{{Expand-section}}

Parangosky had sent Halsey a note in which she asked for her aid in the matter, appealing to her on a professional level to protect ''Infinity'' and its crew despite her less than ideal conditions.<ref>'''Halo 4''', ''Infinity Briefing Packet''</ref> Many of the crew had mixed feelings about bringing her aboard, [[Sarah Palmer]] suspicious of her and feeling she might try to sabotage the ship, [[Thomas Lasky]] sharing her worries but feeling there was no choice. Halsey was unimpressed by the Spartan-IVs assigned to guard her, wryly questioning their competence and general attitude. With a few gestures from her, the artifact began reacting to her, she translating its actions as signs that she should examine the ship's engines. Upon doing so, her conclusion was that the artifact was "communicating" with multiple parts of the ship and transmitting to Requiem. Some time later, she analyzed a Forerunner [[Beacon tower|beam tower]] encountered by [[Fireteam Crimson]] in the location codenamed [[Two Giants]].<ref>'''Spartan Ops''', [[S1/Catherine|S1E3 ''Catherine'']]</ref>

[[File:H4-SO Halsey discover John' status.jpg|left|thumb|250px|Halsey discovering John-117 is alive.]]
Sometime later, she was escorted by [[Gabriel Thorne]] who volunteered to be her security while she continued her research on the Forerunner artifact. As Thorne questioned her about the SPARTAN-II program, she was contacted by an unknown person about the Prometheans.<ref name="dhand">'''[[Spartan Ops]]''', [[S1/Didact's Hand|S1E4 ''Didact's Hand'']]</ref> When Fireteam Majestic brought back the "[[Didact's Gift]]", Halsey noted its design resembled an AI matrix. Upon activating it, it caused the screens in the lab to show memories of [[New Phoenix]], with one of those memories being the Forerunner artifact. Speculating that she had misinterpreted the translocation artifact's true nature, she proceeded to further examine it. Again, she was contacted by the unknown person through her data pad, who, unbeknownst to her, was [[Jul 'Mdama]]. Suspicious of who Halsey was communicating with, Sarah Palmer confiscated her data pad, and gave it to Lasky, who then ordered Halsey to be taken into custody.<ref>'''Spartan Ops''', [[Memento Mori|S1E5 ''Memento Mori'']]</ref>

After a short interrogation, Halsey was returned to her prison cell.<ref>'''Spartan Ops''', [[Scattered|S1E6 ''Scattered'']]</ref> When Roland entered the cell to ask her questions, Halsey took her chance and overrode Roland's protocol, allowing her to control him. Using his authority to be escorted to Lasky's office, Halsey accessed the data onboard ''Infinity'' to find out what had been kept from her about the Librarian, eventually finding that they had kept secret the return of John-117. Infuriated, Halsey contacted 'Mdama, informing that she had deduced he was her helper so that their alliance could free the Librarian. However, Roland was able to restore himself to his normal state and cut off the connection, and Halsey was promptly arrested. When Halsey was brought to Lasky, she slapped the captain lividly, scolding him for not telling her John-117 was alive. The two were interrupted, however, when Promethean forces gained access to the interior of ''Infinity''. Fending off the Prometheans with his Marines, Captain Lasky picked up Halsey and attempted to escort her to safety.<ref name="invasion">'''Spartan Ops''', [[Invasion (Spartan Ops)|S1E7 ''Invasion'']]</ref>
{{Clear}}

===Capture and defection===
{{Quote|multi=more|Halsey|Jul 'Mdama|Halsey|q1=The UNSC just tried to ''execute'' me. So you'll need to offer something other than idle threats if you want me to ''help'' you.|q2=What is it you desire?|q3=That's easy, Jul. I want revenge.|Halsey and 'Mdama make a deal aboard his flagship.}}

Late in the attack, Halsey was kidnapped by a Promethean Knight and teleported to Requiem. When Admiral Serin Osman was informed of this abduction, she chose to finally enact Parangosky's wishes and ordered for Halsey's immediate termination. While Captain Lasky protested against this, instead sending Fireteam Majestic to rescue Halsey, Commander Palmer departed to carry out Osman's order.<ref name="Spops8">'''Spartan Ops''', [[S1/Expendable|S1E8 ''Expendable'']]</ref>

[[File:HTMCC-H4 SO JanusKeyDisplay2.png|thumb|250px|Dr. Halsey meets the [[Librarian]], and learns of the Forerunner artifacts all over the galaxy.]]
Halsey was then taken to the [[Librarian's Rest]], where Jul 'Mdama had her disable the shield previously erected during Doctor Glassman's attempts to access the shrine. As the shield deactivated, she quickly entered the beam of light being produced by the shrine, to 'Mdama's great anger.{{Ref/Reuse|Spops8}} There, she met the Librarian and was given the [[Janus Key]], which gave the location of every Forerunner artifact in the galaxy. After taking the key, Halsey was returned to the shrine, where 'Mdama acquired one half of the artifact. The intervention of Palmer and Fireteam Majestic forced 'Mdama to retreat from the site with Halsey, but not before she threw the key's other half to Thorne. During the firefight, however, Palmer managed to shoot Halsey in the shoulder.<ref name="s1key">''[[Spartan Ops]]'': [[S1/Key|S1E9 ''Key'']]</ref>

Halsey fell unconscious due to her wound and was transported to a Covenant ship, where her left arm was amputated. Later, aboard the ''[[Song of Retribution]]'', 'Mdama told Halsey that he should have killed her for betraying him, but Halsey replied that the UNSC had tried to kill her as well. She agreed to help the Covenant, ambiguously claiming that she wanted revenge.<ref>''[[Spartan Ops]]'': [[S1/Exodus|S1E10 ''Exodus'']]</ref>

===The Janus Key===
{{Quote|no=two
|1=Sarah Palmer
|q1=You're a traitor and a war criminal. That's all there is to it.
|2=Catherine Halsey
|q2=It's awfully convenient for you to think of me that way—isn't it, Palmer? You can't be that naive. You really think I could have pulled off everything I've been accused of without the full support of ONI? Of the entire UNSC? Consider the resources. The budgets. You think those decisions were made unilaterally? Whether it was a signed form or a wink—they approved it all.
|3=Halsey states ONI's hypocrisy
}}
[[File:HE14 Plan.jpg|thumb|250px|left|Halsey and 'Mdama plot against the UNSC.]]
By [[2558#March|March 2558]], the {{UNSCShip|Vociferous}} was put in charge of finding Halsey and 'Mdama.<ref>'''[[Halo: Escalation]]''', ''[[Halo: Escalation Issue 1|Issue #1]]''</ref> At some point on Requiem, Jul's forces had recovered a Forerunner [[Requiem communication artifact|artifact]] that would be able to communicate with the Forerunner-derived engine systems of ''Infinity'', and therefore the artifact would be able to blockade the engines of ''Infinity'' and allow Jul to steal the other half of the Janus Key. On [[2558#July|July 15, 2558]], Halsey made a personal journal entry on her views of the Forerunners and recent events.<ref name="HE13">'''Halo: Escalation''', ''[[Halo: Escalation Issue 13|Issue #13]]''</ref> The next day, Jul's forces [[Battle of Oban|attacked]] [[Oban]], a human colony in the midst of settlement, as advocated by Halsey. She believed that a bold move was the only way to attract ''Infinity''. After the attack failed, 'Mdama's lieutenants called for Halsey's head, however Jul seemingly defended her actions. After ''Infinity'' attempted to enter slipspace for [[Galileo II]] base, 'Mdama's Forerunner artifact forcefully brought it back into normal space and trapped the vessel in an uncharted system. Aboard a {{Pattern|Ket|battlecruiser}}, Halsey informed Jul that they did not need to attack the ship, as the crew of ''Infinity'' would now be willing to hand over the other half of the Janus Key directly.{{Ref/Reuse|HE13}}

At Halsey's suggestion, 'Mdama had a fake Forerunner artifact placed in a Forerunner structure on the nearby [[Aktis IV]]. As per Halsey's plan, Dr. Glassman and the Spartan-IVs of ''Infinity'' discovered the artifact and believed that it was related to the Janus Key. Halsey and Jul watched Glassman's investigation from ''Song of Retribution'' and Halsey revealed that she knew Jul's public persona was a mere façade when 'Mdama expressed mock abhorrence at creating a copy of a "holy" Forerunner object. Meanwhile, Glassman requested for ''Infinity'' to deliver their half of the Janus Key to him on the planet's surface for further analysis. Anticipating this, Halsey ensured that 'Mdama had troops ready to ambush the UNSC convoy carrying their half of the Key. Much to both Halsey's and 'Mdama's surprise, the Pelican carrying the half was shot down before he could give an order. In the confusion, the rest of the Covenant ambush group began the attack. Halsey insisted on personally searching the crash-site, but 'Mdama decided to scourge the crash-site himself, and he ordered Halsey to remain aboard his carrier. Unbeknownst to him, rebel [[Sali 'Nyon]] was responsible for shooting down the Pelican and he claimed half of the Janus Key for himself.<ref name="HE14">'''Halo: Escalation''', ''[[Halo: Escalation Issue 14|Issue #14]]''</ref>

[[File:HE16 Next destination The Absolute Record.jpg|thumb|220px|[[Jul 'Mdama's Covenant|“Covenant”]] [[Supreme Commander]] Jul 'Mdama and Doctor Catherine Halsey collaborate to find the Absolute Record.]]
Some time after 'Mdama had left for the planet, Halsey contacted him from the ''Song of Retribution'' and urged him to focus on the acquisition of the Janus Key rather than the rebellion among his ranks. In response to the developing situation, Jul fulfilled Halsey's earlier request and allowed her to take a Phantom to the surface of Aktis IV.<ref name="HE15">'''Halo: Escalation''', ''[[Halo: Escalation Issue 15|Issue #15]]''</ref> Halsey and a convoy of Phantoms traveled to an island on Aktis IV to meet [[Unidentified Sangheili Minor (Aktis IV)|a defector]] from 'Nyon's forces. After the defector reluctantly gave the half of the Janus Key he had stolen from 'Nyon's base to Halsey, the doctor and her Sangheili escorts prepared to return to ''Song of Retribution''. After Jul had most of Halsey's convoy depart to battle UNSC forces elsewhere on the island, Halsey and the remaining Covenant forces were ambushed by Spartans Palmer, Thorne, and [[Naiya Ray|Ray]]. Palmer pursued Halsey and her guard into the jungle, while the other Spartans eliminated the surviving Covenant forces. After killing her guard, Palmer captured Halsey and led her through the jungle. The two began to argue, with Palmer accusing her of being a traitor and war criminal, and Halsey calling Palmer out for acting as Admiral Osman's puppet and stating that ONI turned her into a convenient scapegoat. As Palmer's judgement became momentarily clouded, Halsey ran off into the jungle. Palmer attempted to pursue, but she was injured and knocked into a crevice by a nearby [[Za'zayara-pattern Harvester|Harvester]]. Halsey contacted 'Mdama and he had a Phantom return her to his flagship.<ref name="HE16">'''Halo: Escalation''', ''[[Halo: Escalation Issue 16|Issue #16]]''</ref>

Shortly after, Jul's forces fled the system with both halves of the Janus Key. Halsey and Jul used the combined Janus Key to project a holographic map, which revealed the approximate location of the [[Absolute Record]].{{Ref/Reuse|HE16}} Hiding within the [[Urs system]], Halsey worked on finding the coordinates of the Absolute Record, on [[2558#September|September 15, 2558]] pinpointed its exact location. Two days later, as the fleet prepared to depart for the Absolute Record, a Phantom carrying Spartans Palmer, Thorne, [[Holly Tanaka]], Dr. Glassman, and [[Ayit 'Sevi]]—a mercenary within 'Mdama's ranks working for ONI—boarded ''[[Breath of Annihilation]]'', intent on revealing the location of the Absolute Record to the UNSC.

===The Absolute Record===
{{Quote|no=two|q1=What do you expect to find in there, Halsey?|Jul 'Mdama|q2=Exactly what the Librarian promised... a new future.|Dr. Halsey|Dr. Halsey entering the Absolute Record}}
[[File:HE21 Begone.jpg|thumb|250px|left|Halsey, the other humans, and 'Mdama are left stranded on small platforms.]]
The fleet arrived at an apparently artificial gas giant with a slipspace portal leading to the Absolute Record. Before the fleet could press forward, slipspace ruptures materialized around the fleet, destroying at least two ships and damaging ''Breath of Annihilation''.<ref name="HE19">'''Halo: Escalation''', ''[[Halo: Escalation Issue 19|Issue #19]]''</ref>  Furious at the damage done to his fleet, 'Mdama blamed Halsey for the loss and threw her across ''Song of Retribution''<nowiki>'</nowiki>s bridge. While Halsey and 'Mdama argued about the situation, she reminded him that once they reached the Absolute Record, they will discover technology beyond their comprehension that will more than compensate for the ships that were destroyed. Halsey further exaggerated that once he was in control of the Absolute Record's "treasures", 'Mdama would be seen as a god. Thus 'Mdama decided to travel to the Absolute Record, with only ''Retribution'' entering the portal while the rest made repairs. As Halsey and 'Mdama prepared to enter the portal, they learned of rumors of the Spartans attacking personnel of ''Breath of Annihilation''. Halsey dismissed 'Mdama's fears and stated that the Spartans could not stop them from reaching the Absolute Record, though she was unaware that Palmer, Tanaka, and Glassman had boarded ''Retribution''. 

The carrier traveled through the portal and arrived into the Record, where Halsey, along with the other humans who had infiltrated the carrier, were detected by a [[Contender-class artificial intelligence|Contender-class]] [[Invariant Bias|Custodian]].<ref name="HE20">'''Halo: Escalation''' ''[[Halo: Escalation Issue 20|Issue #20]]''</ref> After ''Retribution'' was forcefully brought through a portal to a large chamber, Halsey, 'Mdama, and a contingent of Zealots traveled to a lower platform, where Halsey addressed the ancilla and told it that she was selected by the Librarian and her possession of the Janus Key was proof. However, the AI was skeptical of her claims, claiming Halsey could've obtained the Key by force and especially pondering why the other humans felt the need to conceal themselves. The AI had its Sentinels bring the other humans down to the platform, and stated its intent to let each human have a chance to account for its presence at the installation, despite Halsey's assertions that there was nothing to discuss as she had the Janus Key. As she continued to argue with the AI and Glassman, an impatient Zealot attacked a Sentinel, leading to a conflict on the platform. Frustrated, the AI removed the flooring from under the feet of the Sangheili, with Tanaka, Palmer, and Glassman remaining on one platform and Halsey standing on another, 'Mdama managing to grab its edge just in time.<ref name="HE21">'''Halo: Escalation''' ''[[Halo: Escalation Issue 21|Issue #21]]''</ref>

In order to decide who would be the legitimate steward of the Absolute Record, the AI decided on a direct examination. It had both factions isolated and gave them a hypothetical scenario, in which a sapient species (represented by [[Yonhet]]) turned out to have bodies conducive to a Flood vaccine. Abducting and harvesting live beings would give a thirty-five percent chance of Flood-immune material, but receiving dead bodies from the beings would give them a thirty-three percent chance. Despite Jul's advice, Halsey chose live capture while Glassman chose the peaceful option, and the ancilla commended both. It then asked if their opponents in this test should be kept confined or immediately killed, but instead of answering, Halsey hacked the ancilla and shut it down, taking control of the Record for herself.<ref name="HE22">'''Halo: Escalation''' ''[[Halo: Escalation Issue 22|Issue #22]]''</ref>

[[File:HE24-Palmer&Halsey.jpg|thumb|300px|Dr. Halsey ambushed by Sarah Palmer.]]
In the Record, Halsey followed a hologram of the Librarian directing her to dormant design seeds scattered across the galaxy, which she could choose to activate the next step of their plans for human evolution. While she listened, Jul 'Mdama outside expressed his growing impatience with Halsey, and told his warriors in secret to restrain her once she left so to remind her who was in charge. Unfortunately for him, Halsey overheard Jul through the Record's systems and decided now was the time to sever their partnership, giving the order for the installation's Sentinels to attack Jul and his men.<ref name="HE23">'''Halo: Escalation''' ''[[Halo: Escalation Issue 23|Issue #23]]''</ref>

While Halsey made preparations, Palmer, Tanaka, and Glassman came in contact with a Sentinel containing the backup memory of the Record's ancilla. With their aid, the AI regained control of the facility and barred Halsey from controlling it further. Over Halsey's protests, the custodian admitted that Halsey had nearly passed its test and would've been given the Record if she hadn't been so impatient to steal it. The custodian thus took the Janus Key and began pulling the Record back into slipspace. Shortly afterward, Halsey was recovered by Jul's forces and brought back aboard the ''Song of Retribution'', unaware that she had tried to betray them and under the impression that the ancilla had sent the Sentinels.<ref name="HE24">'''Halo: Escalation''' ''[[Halo: Escalation Issue 24|Issue #24]]''</ref>

===The Guardians===
{{Quote|I tried to warn you this was happening. Cortana is no longer an asset, Captain. She is a danger.|Halsey stresses the enormity of the threat posed by Cortana to Captain [[Thomas Lasky]].}}{{Ref/Reuse|H5GG}}
[[File:Halsey.PNG|thumb|300px|By the time of his death, Jul 'Mdama had begun to think having Halsey around was more trouble than it was worth.{{Ref/Reuse|H5GOMI}}]]
Near the end of September Doctor Halsey managed to contact ONI and the {{UNSCShip|Infinity}} and provide Captain Lasky with coordinates at which she could be found.{{Ref/Reuse|HBB1}}<ref name="H5GO">''[[Halo 5: Guardians]]'', ''[[Osiris (level)|Osiris]]''</ref> They pointed to the planet [[Kamchatka]] in the [[Caspar system]], where a [[Forerunner]] communication hub had recently flared to life and attracted the attention of both [[Jul 'Mdama|Jul]] and the [[UNSC]].{{Ref/Reuse|H5GO}}<ref name="WaypointKamchatka">[https://www.halowaypoint.com/en-us/universe/locations/kamchatka '''Halo Waypoint''' - ''Kamchatka'']</ref> Upon reaching Kamchatka Halsey set about studying the nature of various incoming signals which were bouncing off of the Forerunner objects on the planet, akin to echolocation.<ref name="H5GOMI">''[[Halo 5: Guardians]]'', ''[[Osiris (level)|Osiris]]'' [[Mission Intel#Osiris|mission intel]]</ref> Halsey concluded that [[Cortana]] was searching for [[Guardian Custode|something]] but could not guess at what that something might be. At Halsey's direction, a structure that was the focal point for one of the signals was eventually penetrated by the [[Jul 'Mdama's Covenant|Covenant]] forces with her. In her research notes Halsey bemoaned the way in which her work was being hampered by their overriding concern for ceremony, leaving her still without much information she did not have before they breached the structure. Some time later, however, Halsey obtained scans of new [[Forerunner symbols|glyph]]s, including one that she was sure had never been observed before. After running it through a system she found that it bore a resemblance to an ancient [[Sangheili]] symbol for a [[Sangheili mythology|demon]] that sleeps in the ground and must not wake. How this symbol might relate to the symbol, she was still unsure. Halsey further noted that the readings she would expect from a Forerunner structure the scale of which they inhabited were erratic at best, leading her to then wonder if perhaps Cortana was trying to access technology on Kamchatka and other locations directly, but failing.{{Ref/Reuse|H5GOMI}} 

By October 17 the UNSC had been keeping tabs on the consolidation of the bulk of Jul's fleet at Kamchatka for weeks.{{Ref/Reuse|HOSFM11}}<ref name="HOSFM92">''[[Halo: Official Spartan Field Manual]]'', ''page 92''</ref> Less than a week after that date (and at three weeks since Halsey contacted the ''Infinity'') a native defense system on Kamchatka was disabled, but Halsey was unable to bring its corresponding alert system down soon enough.{{Ref/Reuse|H5GOMI}}<ref name="HOSFM11">''[[Halo: Official Spartan Field Manual]]'', ''page 11''</ref> As a result, mechanical [[Promethean]] constructs arrived at Kamchatka within the hour and [[Battle of Kamchatka|attacked]] the Covenant.{{Ref/Reuse|H5GOMI}} That same day, the [[Spartan-IV]]s of [[Fireteam Osiris]] were deployed to retrieve Halsey from Jul 'Mdama's custody.{{Ref/Reuse|H5GO}} They found she and 'Mdama on a cliffside balcony of a temple structure. There Halsey claimed to be trying to access the [[Domain]] despite several problems, such as those relating to [[Slipstream space#Reconciliation|causal reconciliation]]. Jul made his impatience with her efforts clear and also demanded that she afford him respect, but this only elicited taunting on her part over his loss of the [[Promethean]]s. Finally, she declared that their current location was unsuitable for [[Wikipedia:Triangulation|triangulation]] should Cortana make another transmission. This enraged Jul, who scolded her for failing to deliver results after weeks of "chasing shadows", as he put it. It was at that moment that Osiris attacked Jul and his guards, killing them all. Spartan [[Jameson Locke]] approached the doctor after pulling his [[combat knife|knife]] from Jul's neck and let her know that Captain Lasky wanted to see her. To this she sarcastically replied that it had taken them long enough.{{Ref/Reuse|H5GO}} Halsey accompanied Osiris back to the ''Infinity'' via Pelican.<ref name="H5GBT">''[[Halo 5: Guardians]]'', ''[[Blue Team (level)|Blue Team]]''</ref> Upon landing within Docking Bay 11 the five of them were met by Lasky and [[Sarah Palmer]]. Catherine chided the captain for not coming to get her sooner and had him assure her they would talk about that once they were somewhere with more privacy. Palmer took Halsey by the arm and began to lead her way but even as they went she couldn't help but ask Lasky for any information he had about Cortana's actions, which he flatly ignored.{{Ref/Reuse|H5GBT}}{{Ref/Note|At some point Halsey told Locke "Once this is over, after all I have done, [[ONI|they'll]] order you to kill us both." At what point she told him this, what ongoing event or events she was referring to, or who she was asserting he'd be ordered to kill in addition to her are presently unknown. This line plays during the opening cutscene of ''Halo 5: Guardians'' while both Halsey and Cortana are shown, suggesting Cortana may be the additional target referred to. In addition, Halsey is known to have at some point assisted a [[unidentified AI|"non-volitional" A.I.]] located within a secure ONI facility after it was tasked by Locke with determining vulnerabilities within Mjolnir armor.}}
[[File:She's alive-.png|thumb|left|350px|Halsey, Palmer, Roland, and Lasky discuss Cortana and the Master Chief.]]
By October 23 the ''Infinity'' had arrived in the [[Crow's Eye Nebula]].{{Ref/Reuse|H5GBT}}<ref name="WaypointLinda-058">[https://www.halowaypoint.com/en-us/universe/characters/linda-058 '''Halo Waypoint''': ''Linda-058'']</ref><ref name="TD">[[Troy Denning]] on Twitter [https://twitter.com/TDenningauthor/status/932052034701942784]</ref> At 0630 hours that day [[Linda-058]], [[Kelly-087]], [[Frederic-104]], and [[John-117]] were declared absent without leave, having made an unsanctioned departure from the nebula in [[ONI Acrisius|a]] stolen {{Class|Winter|prowler}}.{{Ref/Reuse|H5GG}}{{Ref/Reuse|H5GBT}} Spartan Palmer escorted Halsey to the ''Infinity''{{'}}s bridge later that day, where she immediately began pressing the matter of Cortana once more to the captain, stressing how dangerous she had become through accessing the Domain and taking control of [[Guardian Custode|devices]] which had begun to cause damage on a number of colonies.{{Ref/Reuse|H5GG}} Lasky informed her that the Master Chief had reported being contacted by Cortana, which Halsey saw as potentially disastrous. She was then told that he'd gone in search of her and was shocked at the notion that Lasky would have let him go, but he explained that John was not acting independently. Halsey began to speak on why John was unequipped to deal with Cortana as a threat but was interrupted by [[Roland]], who until that point had been unaware of her continued survival. He questioned why the doctor was so quick, in his mind, to label Cortana a threat or a danger, seeing as she was the one who had created her to begin with.<ref name="H5GG">''[[Halo 5: Guardians]]'', ''[[Glassed]]''</ref> Two days later Fireteam Osiris was deployed once again, but this time with the goal of apprehending Blue Team and the stolen [[prowler]].{{Ref/Reuse|H5GG}}<ref name="HFWR">''[[Halo: Fractures]]'', ''[[What Remains]]''</ref> The AWOL Spartans had been followed to [[Meridian]], a moon of [[Hestia V]].{{Ref/Reuse|H5GG}} Osiris failed to stop them, as they managed to board a [[Guardian Custode]] which had long been buried beneath the moon's surface and had now slipped away.<ref name="H5GE">''[[Halo 5: Guardians]]'', ''[[Evacuation]]''</ref> As such, The fours were forced to return to the ''Infinity'' empty-handed.{{Ref/Reuse|H5GE}} The day after this Locke and Lasky met Palmer and Halsey on the bridge and Locke let it be known that a construct they'd met on Meridian calling itself the [[Warden Eternal]] had confirmed the doctor's theory that Cortana was behind the Guardians' ongoing reactivations.<ref name="H5GR">''[[Halo 5: Guardians]]'', ''[[Reunion]]''</ref> Halsey then turned their attention to [[Sunaion]], a religious site on [[Sanghelios]] where she had discovered another Guardian still lay buried. Palmer and Roland took over from there, explaining that if they could feed coordinate data from the Meridian Guardian to the one on Sanghelios it could lead them right to [[Genesis|wherever]] Blue Team had vanished to.{{Ref/Reuse|H5GR}}

===Sanghelios===
{{Quote|I'm playing along with your protocol here, Thel. If the [[SPARTAN-IV program|fours]] bring me an active Constructor, I can interface with the Guardian. It will receive Cortana's signal the moment it activates and initiates slipspace, but I think I can make sure it leaves the sea before it jumps. I'll get it in the skies over Sunaion, like you asked.|Catherine records a message for Thel 'Vadam, the Sangheili Arbiter.}}{{Ref/Reuse|H5GAMI}}
After arriving in the [[Urs system|Urs-Fied-Joori system]] on [[2558#October|October 27]] Halsey accompanied [[Sarah Palmer|Palmer]] to a waiting [[D79-TC Pelican]] in the process of being loaded up for travel to [[Sanghelios]].{{Ref/Reuse|H5GSOS}} At the approach of Spartans [[Jameson Locke|Locke]] and [[Olympia Vale]] Palmer let it be known that the doctor was trying to find a way to communicate with the [[Guardian Custode]] on the planet. Halsey assured Locke she'd have a briefing for him once they were all planetside.<ref name="H5GSOS">''[[Halo 5: Guardians]]'', ''[[Swords of Sanghelios (level)|Swords of Sanghelios]]''</ref> [[Fireteam Osiris]] soon met up with [[Thel 'Vadam|the Arbiter]] and following this Halsey and Palmer joined them at a camp the [[Swords of Sanghelios]] had set up in [[Nuusra]].<ref name="H5GA">''[[Halo 5: Guardians]]'', ''[[Alliance]]''</ref> Whilst Locke was treating with 'Vadam, [[Cortana]]'s voice suddenly rang out from within their meeting tent, prompting Halsey and Palmer to both rush inside. Halsey noted that she'd touched every networked device in the camp just then and concluded she must know of the Guardian they were after. 'Vadam agreed to assist in the effort to get to it at [[Sunaion]] but only on the condition that victory would be assured when they finally moved on the city. Pledging they'd deploy within the hour, Locke told Halsey to have her plan ready by then.{{Ref/Reuse|H5GA}}
[[File:H5G HalseySanghelios.PNG|thumb|350px|While in the Arbiter's camp, Doctor Halsey's amputee status was taken by the [[Unggoy]] and self-proclaimed biologist [[Gribyam]] to support [[Catherine-B320|theories]] that [[human]] females signal maturity by losing appendages.{{Ref/Reuse|H5GBTSMI}} He further hypothesized that she would soon begin to release spores and spin a cocoon of "rich meat-silk".{{Ref/Reuse|H5GBTSMI}}]]
While she continued to devise a strategy Halsey recorded a status update for the [[Arbiter]], [[Thel 'Vadam]], in which she assured him the Guardian would be in the sky over Sunaion before it initiated a [[slipspace]] jump, as he had asked.<ref name="H5GAMI">''[[Halo 5: Guardians]]'', ''[[Alliance]]'' [[Mission Intel#Alliance|mission intel]]</ref> In return for her cooperation with his request she also made one of her own for more intelligent assistants to aid her and urged him to loosen the security placed on her.{{Ref/Reuse|H5GAMI}} Sometime after this she contacted Locke over an open communications channel to let him know she'd prepared the briefing but preferred to discuss it in person to avoid being eavesdropped upon.{{Ref/Reuse|H5GA}} From atop a [[Forerunner]]-built structure overlooking the camp she waved the Spartans over to her as they neared and then proceeded to introduce them to what a [[Constructor]] [[sentinel]] was. She explained that if one could be acquired from the support stations which riddled the hills around them then she could use it to interface with the Guardian. She further informed them that Palmer had the location of one such station.{{Ref/Reuse|H5GA}} In a supplemental status update for Thel, she pointed out that while making stubborn claims to not need her or the Guardian he ought to remember the [[ONI|organization]] she represented and its history.<ref name="H5GBTSMI">''[[Halo 5: Guardians]]'', ''[[Before the Storm]]'' [[Mission Intel#Before the Storm|mission intel]]</ref> She hoped that this would get him to show her some respect and signed off by claiming this was to be her last mandatory update.{{Ref/Reuse|H5GBTSMI}} Osiris secured a Constructor before the suns had set and returned to the camp with it.<ref name="H5GBTS">''[[Halo 5: Guardians]]'', ''[[Before the Storm]]''</ref> Halsey observed that it seemed to be working as she had planned for it to but told Locke's team that it could take some time until she was finished calibrating it. She then let them know that Palmer wished to see them. When she was ready, she called Osiris back over to her spot on the Forerunner structure, which she informed them she was using to upload the coordinates recorded on [[Meridian]] into the sentinel. She wanted them to be ready to go as soon as she signaled it was time but admitted it might before hours until then. However, the Constructor suddenly took off just then, flying toward Sunaion. As Osiris and the Swords of Sanghelios prepared to follow it Halsey made sure Locke knew Cortana had been built from a matrix of her own mind, cautioning him that like her, she would take drastic measures if she thought they served the greater good. The [[Domain]], she added, would give her incredible power with which to enact those measures. As Locke walked away she called out to him again and pleaded with him to stop Cortana but to bring [[John-117|John]] home to her.{{Ref/Reuse|H5GBTS}}

Palmer had planned to get the doctor off-world once the [[Battle of Sunaion|attack]] on the ocean city began, but she and Halsey eventually arrived at the battle near its end.{{Ref/Reuse|H5GBTS}}<ref name="H5GBOS">''[[Halo 5: Guardians]]'', ''[[Battle of Sunaion (level)|Battle of Sunaion]]''</ref> The Guardian had risen above the waves by that point and was preparing to depart, so Palmer meant to pick up Osiris to deliver them to it before it did so.{{Ref/Reuse|H5GBOS}} Halsey could not bear to even keep her eyes open for very long as the conflict rained plasma fire all around them. Palmer managed to get the other Spartans to the Guardian, but in the process their Pelican's left thruster was struck by a {{Pattern|D'nomlhe|Banshee}}'s [[fuel rod]] and set ablaze. Though it seemed as if Palmer would be able to get them out of there regardless, the Guardian then sent out an [[attenuation pulse]] which neutralized the dropship's power and sent it spiraling toward the [[Csurdon Sea]] below.{{Ref/Reuse|H5GBOS}}

===On the run===
{{Quote|I'm in my mid-sixties, I have one working arm, and we're on the most heavily-secured UNSC starship in the galaxy, with an erratic slipspace trajectory to avoid being detected by the Guardians. Tell me, again, how exactly is it that I am the danger here?|Halsey pushes back against the assertion that she is a dangerous asset.}}{{Ref/Reuse|lootcrate12}}
[[File:H5G HalseyEnding.PNG|thumb|left|300px|Catherine had not seen Kelly, Linda, and Fred since she had been arrested over five years ago and had not seen John since she'd fled to [[Onyx]] around five more months before then.<ref name="HG15">''[[Halo: Glasslands]]'', ''Chapter 15''</ref>{{Ref/Reuse|HBB1}}<ref name="HFS30">''[[Halo: First Strike]]'', ''Chapter 30''</ref>]]
Halsey and Palmer both managed to survive the downing of their Pelican and by the next day they had made it to [[Thel 'Vadam|the Arbiter]]'s encampment in [[Nuusra]].<ref name="HBB1">''[[Halo: Bad Blood]]'', ''Chapter 1''</ref> Using the [[Forerunner]] technology she had been fiddling with upon first arriving on the planet, she was able to receive a coded message from [[Roland]] on the {{UNSCShip|Infinity}}, who informed the doctor that [[Earth]] had been [[Subjugation of Earth|taken offline]] by the rogue A.I.s and that they had just managed to escape. He said the ship was now slipspace-hopping on a random trajectory but would be showing up off the far side of [[Suban]] the next day and remaining there for fifteen minutes. The coordinates the A.I. provided could be reached in a matter of hours with space-capable transportation. Fortunately, after darkness had fallen over the region the approach of [[India 127|a Pelican]] drew she, Palmer, 'Vadam, and two other [[Swords of Sanghelios]] to emerge from a tent to meet it. When it landed and opened its rear hatch, Spartan [[Jameson Locke|Locke]] and [[John-117|John]] were the first two individuals to emerge and present themselves before both of their respective teams followed suit. Having not seen John for over six years, she told him it had taken him long enough. When the Arbiter insisted that both [[Blue Team]] and [[Fireteam Osiris]] join those gathered for a meal before departing, Halsey clarified to him that they wouldn't be leaving that night. Although the possession of a working [[D79-TC Pelican]] would now afford the humans passage off [[Sanghelios]], the ''Infinity'' would not be arriving until 1800 hours the following day. [[Edward Buck]] questioned the trustworthiness of Roland once Catherine explained the situation but she rebutted that if he'd been compromised they'd already be dead. Midway through the meal of [[colo]] and [[kuscatu]] served by their [[Sangheili]] hosts Halsey disappeared to chat with John, [[Frederic-104|Fred]], [[Kelly-087|Kelly]], and [[Linda-058|Linda]].{{Ref/Reuse|HBB1}}

A little less than an hour before sunrise the next day the Spartans and Halsey all piled into the Pelican.{{Ref/Reuse|HBB1}} As the Arbiter bid farewell to John and voiced his confidence in their ability to combat the new threat the [[Created]] posed, the Sangheili shot Halsey a meaningful glance which she ignored with a haughty sniff. While ''en route'' to the rendezvous Halsey pointed out that Sangheili resistance was likely drawing the attention of the [[Guardian]] attempting to pacify the world just then, again arguing that they'd already be dead if they'd been detected. With about twenty minutes until the ''Infinity'' was due to arrive Buck broke out a pack of playing cards and asked if anyone was up for [[Wikipedia:Hearts|Hearts]] but Halsey ignored him, as she was working on a tablet she'd scrounged up. Buck managed to get her attention by referring to the [[Wikipedia:Queen of spades|queen of spades]] as a "Halsey" a couple of hands into the game, but she still gave no response other than to announce that their window was approaching. The gargantuan [[Infinity-class supercarrier|supercarrier]] arrived almost exactly on schedule and Halsey had secured all her things by then. As Kelly docked the Pelican in the ship's Portside Bay Five Buck drew Halsey's attention yet again when he laughed out loud upon realizing his longtime lover [[Veronica Dare]] was aboard.{{Ref/Reuse|HBB1}} The doctor and the Spartans were met in the bay by a lieutenant who had come to escort she, Palmer, John, and Locke to the bridge to see Captain [[Thomas Lasky|Lasky]].<ref name="HBB2">''[[Halo: Bad Blood]]'', ''Chapter 2''</ref> Following that meeting Lasky had Doctor Halsey confined to a workspace and the ''Infinity'' began a series of randomized [[slipspace]] jumps in order to avoid detection by Cortana's [[Guardian Custode|Guardian]]s, emerging from slipspace at its first vector point that very day.<ref name="lootcrate12">''[[Halo Legendary Crate]]'' ''[[Halo Legendary Crate/Data Drops|Data Drop #12]]''</ref>{{Ref/Reuse|HBB2}} That same day [[Roland]] answered a distress call from the {{UNSCShip|Sentry of El Morro}} with the affirmation that the supercarrier was on its way to assist it.<ref name="HFRW">''[[Halo: Fractures]]'', ''[[Rossbach's World (story)|Rossbach's World]]''</ref> By the start of November, the ship exited slipspace at one point to receive the recently reassembled Spartan team [[Alpha-Nine]].<ref name="HBB21">''[[Halo: Bad Blood]]'', ''Chapter 21''</ref>{{Ref/Note|The presence of [[031 Exuberant Witness]], [[monitor]] of the [[Builder]] world [[Genesis]], as a [[multiplayer]] announcer in ''[[Halo 5: Guardians]]'', may indicate that the ''Infinity'' also at some point received her. [[343 Industries]] writer [[Jeff Easterling]] has said, however, that Witness' presence on the ship may not be entirely canonical.}}
[[File:LC 12 doc4.jpg|thumb|350px|This image was captured by Spartan [[92738-61842-LC]], who wore their helmet while interviewing Halsey in order to record the interaction.{{Ref/Reuse|lootcrate12}}]]
By [[2559#January|January 24, 2559]], they were still on the run, performing erratic jumps to evade discovery.{{Ref/Reuse|lootcrate12}} That day, at just after 1204 hours, Halsey was approached by a Spartan from [[Fireteam Apollo]] with the serial number [[92738-61842-LC]]. This individual had been tasked by Captain Lasky with investigating what was being dubbed "the Guardian Incident". Halsey pointedly asked how they had gotten clearance to talk with her and was made aware of the priority-one directive given to them by the captain. After then confirming she was being recorded, the Spartan informed her they were there to talk about [[Cortana]]. Halsey was interested to hear what their investigation had unearthed so far, but they reported not being authorized to share anything further than their having concluded that the cognitive duress and strain Cortana had sustained since the discovery of [[Installation 04]] was partially responsible. The Spartan's first questions for the doctor concerned Cortana's creation, and Halsey was soon defending her actions incumbent in that process. She also refused to reveal what had become of the clones of herself she had made, claiming that was still classified even for them. Asked what she thought the best explanation for what had happened was, Halsey recalled Cortana's first words and theorized she was simply doing she had to in order to keep "the game" from ending. Halsey then quoted the Greek philosopher [[Wikipedia:Epictetus|Epictetus]] and suggested Cortana was the answer to his thought experiment regarding the harm in saying "Tomorrow you will die," while kissing one's child. When her interviewer asked what she thought the solution to stopping her was, Catherine ignored the question since she doubted coming up with that would be part of a Spartan's directive and was convinced she'd been locked away for that purpose. 92738-61842-LC countered that she'd been locked up because of her repeated protocol violations, which only led to further argument and  the Spartan finally choosing to take their leave. Before they went, Halsey shared the [[Cortana Letters#First letter|last thing]] Cortana had said to her.{{Ref/Reuse|lootcrate12}} The Spartan asked what her words were supposed to have meant, but Halsey could only say that she had been hoping they were able to explain them to her.{{Ref/Reuse|lootcrate12}}{{Ref/Note|What Halsey indicated Cortana had last said to her is quoted from the first of the [[Cortana letters]], a series of emails produced prior to the release of ''Halo: Combat Evolved''. Whether or not Cortana said the things she did to Halsey prior to her slipping away from [[Eridanus Secundus]] in [[2552]] or at some point after, perhaps following her accessing of the [[Domain]], is unknown.}}.

At some point following the beginning of the [[Created conflict]], Halsey started working on the [[MJOLNIR Powered Assault Armor (GEN3)|MJOLNIR GEN3]] platform, designing the PANSPEC energy shielding alongside Doctor Henry Glassman,{{Ref/Book|Halo Encyclopedia (2022 edition), page 84}} and personally selecting the new design for the [[MJOLNIR Powered Assault Armor/Mark VII#GEN3|GEN3 Mark VII]] armor from Materials Group's [[Project KEYSTONE|KEYSTONE development program]].{{Ref/Site|Id=CF108|D=01|M=6|Y=2020|URL=https://www.halowaypoint.com/en-us/news/despite-distance|Site=Halo Waypoint|Page=Canon Fodder - Despite Distance}} She also took interest on the fireteam synchronization features of the [[SOLDIER-class Mjolnir#GEN3 Overview|GEN3 Soldier]] helmet.{{Ref/Game|Halo Infinite, Armor Hall: Soldier - Helmet Description "The latest iteration of the SOLDIER helmet features a new revision of Materials Group's combat catalyst firmware. The fireteam synchronization features remained unfinished, but Dr. Halsey's interest may accelerate development."}} On [[2559#September|September 19, 2559]] Doctor Halsey made modifications to [[John-117]]'s GEN3 Mark VI armor, itself having first been created on [[2559#February|February 10, 2559]].<ref name="BSI">''Halo Infinite'', [[Step Inside]]</ref><ref name="DH">''[[Discover Hope]]''</ref>

===Stopping Cortana===
{{Cleanup}}
In [[2559#October|October 2559]], now sporting a prosthetic arm, Halsey convinces Captain Lasky to [[Operation: WOLFE|return]] to [[Reach]] for some assets that she had kept in a secret cryovault inside of the destroyed [[CASTLE Base]]. The UNSC forces end up coming up against the [[Banished]] and their allies, but [[Blue Team]] are successful in retrieving Halsey's cryobins and lockbox. Upon their return to the {{UNSCShip|Infinity}}, Halsey greets the Spartans alongside Captain [[Veronica Dare]] of ONI. After briefly bantering with John, she is visibly distressed by the bad state of Blue Team and John is forced to steady her. Halsey calls the Spartans her greatest achievement and asks if John understands that, but he asks if she's alright in return which she evasively responds to. Seeing Halsey so upset by their return in such a bad state causes John to consider her reaction, considering that she had sent them on the mission in the first place and she had seen Spartans return in as bad a state or not return at all. John wonders if, based on some of the things that she has said, Halsey regrets some of her work or at least some of the things that had been necessary to create the Spartans. However, despite knowing the extent to which Halsey had gone, John is glad that she had done it and he and his fellow Spartan-II's are proud of what they had become and what they had done to save humanity. While John wants to tell her that, he is unable to find the words to express himself adequately to her. After recovering her composure, Halsey confirms that the mission was successful and warns him that this isn't going to be easy, but it's the only option that they have. As the approach of a [[Guardian]] is detected, they witness several Pelicans and an [[Albatross]] dropship turn back because they won't be able to reach the ''Infinity'' in time, leaving them stranded on Reach for possibly years to come. Halsey reassures the others that the people that will be stuck on Reach are soldiers who can survive indefinitely on Reach and they won't be alone. Halsey comments that she almost envies them and John agrees with her assessment of the chance of the people that are getting stranded.{{Ref/Novel|Id=SoR|SoR}}

In [[2559#December|December 2559]], using her remaining [[flash cloning|cloned]] brains from Cortana's creation that Blue Team had recovered for her from Reach, Halsey successfully creates [[the Weapon]], an exact copy of [[Cortana]], to be used in a mission to [[Installation 07]] to lock down the rogue AI and transport her back to the ''Infinity'' for deletion with the Weapon being programmed to be deleted once her mission is over. However, Halsey is less than pleased when Lasky reassigns the rest of Blue Team elsewhere and sends John alone with the Weapon to stop Cortana.{{Ref/Game|Id=Audio logs|HI|Audio log (Halo Infinite)#Infinity's Approach 2|UNSC Audio log|Detail=Infinity's Approach #03 - Duty Clearance}} While traveling the ring and seeing Cortana's memories, the two witness such moments as Halsey first giving Cortana to John and her arguing with Captain [[Jacob Keyes]] about Cortana. John later tells the Weapon that Halsey had removed any information that could've compromised the AI from her, but she had made the Weapon with copies of all of the same systems and routines as Cortana, effectively making the Weapon a version of Cortana as she was if she had never met John.

It is unknown if Halsey herself was onboard the ''Infinity'' when the ship was apparently destroyed over Installation 07 and what became of her if she was.{{Ref/Game|Id=Hi|Hi}}{{Ref/Note|At some point following the cessation of the war with the Covenant, Doctor Halsey eulogized [[Spartan-B312]] of [[NOBLE Team]], commemorating his sacrifice in laying down his life so that the {{UNSCShip|Pillar of Autumn}} could escape [[Reach]] with [[Cortana]]. Thanks to him, [[Installation 04]] was discovered and the events which led to the Covenant's [[Great Schism|downfall]] were set in motion. This dialogue plays at the [[Lone Wolf|end]] of ''[[Halo: Reach]]'' while the planet is shown to be [[Terraforming|recovering]] on [[2589#July|July 7, 2589]], but the precise date for her words cannot be definitively determined.}}

==Personality and traits==
{{Quote|If people would just share things with me, I could solve all the world's problems.|Dr. Halsey musing to herself over the UNSC withholding data from her.{{Ref/Reuse|invasion}}}}
[[File:KatCarterHalsey.jpg|thumb|275px|Halsey addresses [[Carter-A259]] and [[Catherine-B320]].]]
Immensely intelligent, reclusive and somewhat self-centered, Halsey is almost entirely devoted to her work and the pursuit of knowledge to advance humankind. She has little regard for rules, authority or bureaucracy, in most cases viewing them as little more than obstacles to her work. While her singleminded dedication and seemingly detached personality have led to many perceiving her as devoid of morals or emotions, she has nonetheless shown to care about the few people close to her and has been deeply affected on a personal level by the moral implications of her work.

Halsey tends to be professional and authoritative when speaking to people, which she rarely does outside of meetings and briefings. She has little patience for extraneous detail, wanting the important facts out of them and then concluding their meeting.<ref>'''Halo: Reach''', ''[[ONI: Sword Base]]''</ref> Considered extremely difficult to read,<ref name="goo345">'''Halo: Ghosts of Onyx''', ''page 345''</ref> she rarely voices her current emotions, and often observes people while speaking to them to discern hidden details. Having grown accustomed to keeping secrets, she may appear enigmatic and manipulative at times; while she despises efforts to withhold information from herself, she has a tendency of laying her own plans in advance and only divulging information when it becomes relevant.{{Ref/Reuse|goo341}} She prefers to work with her authority unchallenged, and does not appreciate being bogged down by having to explain herself, especially in a hurry. On Onyx, this led to a conflict between her and [[Kurt Ambrose]], who eventually confronted the doctor over her self-assumed leadership and instead asserted his own command over the mission, much to Halsey's dismay; despite this, she remained confident in Kurt's leadership ability.<ref>'''Halo: Ghosts of Onyx''', ''pages 257-258''</ref> When necessary, however, Halsey has been very verbose about describing the subject at hand, namely if attempting to convince someone of its importance. Outside of professional contexts, her persona has been considered charming and likable by some.<ref name="fs225">'''Halo: First Strike''', ''page 225''</ref>

Above most of her compatriots in terms of both intelligence and knowledge, Halsey prefers to perform her most important work personally, rarely entrusting particularly significant scientific tasks to others. She often assumes a certain ownership over her work, most prominently seen with her referring to the Spartan-IIs as "her" Spartans and reacting negatively to others co-opting her work. Halsey is keen to note any flaws she finds in her colleagues' work, and quick to point out when she considers someone unqualified.{{Ref/Reuse|Composer logs}}{{Ref/Reuse|journal}} However, she also has an eye for talent and will give credit for any accomplishments she sees as remarkable.{{Ref/Reuse|journal}} It is not uncommon for her to have respect for someone and yet also dislike them, as shown in the cases of her student [[Ellen Anders]]<ref>'''Dr Halsey's journal''': (Halsey: "If that Anders girl was still around, she would have come in handy right about now. She was always so difficult, but this has, without a doubt, become a shared interest.")</ref> and the Spartan-III [[Catherine-B320]].<ref>'''[[Halo: Reach ViDoc: A Spartan Will Rise]]''': (Halsey: "Kat, Noble Two. She is brilliant. There are no technical hurdles she can't overcome. But her curiosity borders on insubordination."</ref> Halsey is an atheist, lacking belief in the existence of any god.<ref>'''Halo: Ghosts of Onyx''', ''page 157''</ref>

Halsey's intelligence is unquestionable but her judgment is not always correct. Although bearing the guilt of the Spartan program, her sense of right and wrong has differed greatly. When sure it will produce results, Halsey is not above breaking the law to achieve her goals, such as cloning herself to produce Cortana, using a stolen Slipspace engine for her fractal AI experiment, and kidnapping [[Kelly-087|Kelly]] and fleeing to Onyx. "The ends justify the means" appears to be her ideology, as an interrogator after she was arrested accused her of. To soothe her conscience, she often deliberately reduces the wording of harsh consequences, such as telling John that the augmentations was just his next mission, or [[Soren-066]] that the pain from his botched surgery would eventually go away.<ref>'''Halo Evolutions''', "Pariah", ''page 40''</ref>

[[File:Journal Family Tree.png|thumb|left|250px|A family tree drawn by Halsey, of all the people whose lives she affected.]]
Dr. Halsey is not keen on losing, as seen when she kept losing at a game of Twenty Questions with her Spartans and soon quit playing.<ref>'''Halo: First Strike''', ''page 140''</ref> She was also resentful of attempts to keep information from her, demanding to know everything the UNSC could provide to keep them from deceiving her. Any attempts to keep her in the dark would eventually fail once she'd begin hacking, since Halsey often programmed backdoors into everything she designed.{{Ref/Reuse|invasion}}<ref>'''Halo: First Strike''', ''page 128''</ref> According to [[Black-Box]], Halsey was not too different from an AI, being fueled by a desire to know everything she could.{{Ref/Reuse|Halo page 358}} She is easily absorbed by her work and the acquisition of knowledge to the point of ignoring more pressing matters; on Onyx, she requested the rest of the group to leave her behind in the world's map room in order to learn more until being snapped out of her reverie by a Covenant attack.<ref>'''Halo: Ghosts of Onyx''', ''page 312''</ref>

Halsey has a notable fondness for classical music, especially [[Wikipedia:Claude Debussy|Debussy]]. When getting to work, Halsey has a habit of issuing a series of commands to AIs in a rapid sequence (often ending with her requesting the AI to play one of her preferred pieces of classical music), which has on some occasions given less sophisticated AIs a pause to process the information.{{Ref/Reuse|fs123}}<ref>'''Halo: The Fall of Reach''', ''page 16''</ref><ref name="goo148">'''Halo: Ghosts of Onyx''', ''page 148''</ref> She has a bad habit of keeping a messy office and drinking cold coffee, tending to prepare the drink and then become distracted by work, only remembering it hours, sometimes days, later.<ref>'''Halo: The Fall of Reach''', ''page 230''</ref><ref>'''Halo: First Strike''', ''pages 125-126''</ref> She preferred darker coffees than those grown on Reach.<ref>'''Dr. Halsey's personal journal''', ''December 4, 2510''</ref> On January 9, [[2535]] she met with [[Chief Petty Officer]] [[J. G. Jimes]] in order to procure quality Beniese coffee.<ref>'''Dr. Halsey's personal journal''', ''January 7, 2535''</ref>

An ONI-commissioned [[Hemley & Aubourn Behavior Analysis|psychological evaluation]] conducted by [[B.M. Parkes]] in [[2551]] largely correlated with observed aspects of Halsey's personality, demonstrating exceedingly high cognitive performance (which was noted to possibly obfuscate the rest of the results) but a markedly low score in teamwork and an uncommonly high "liability" index, 64% higher than the average ONI rating due to her demonstrated disregard for authority. The analysts suggested that she be placed under closer surveillance, with two or three handlers accompanying her at all times at both of her primary working sites on Reach.{{Ref/Reuse|DD3}} Halsey designed the most recent model of AI matrix compiler used in the [[Cognitive Impression Modeling|scanning of human brains]] to create smart AIs. This particular compiler was still in use by [[2557]].<ref name="Composer logs">'''Halo 4''', campaign level ''[[Composer (level)|Composer]]'', [[Audio log (Halo 4)|Audio log]]</ref>
{{Clear}}

===SPARTAN-II program and guilt===
[[File:Halsey Eyes.png|thumb|300px|Halsey battled guilt over the SPARTAN-II project. She knew that moral lines had been crossed to save humanity.]]
{{Quote|Spartans never die? If only that were true.|Catherine Halsey, reflecting her guilt over the SPARTAN-II program.<ref>'''''Halo: First Strike''''', ''page 249''</ref>}}
Dr. Halsey carried extraordinary guilt because of the [[SPARTAN-II program|SPARTAN-II project]], in the feeling that she had exploited the children and destroyed their lives. Although she continued to support the Spartans and gained monumental prestige for her efforts, she also felt responsible for each one who died. She could never bring herself to justify the Spartans' exploitation as a necessary sacrifice.{{Ref/Reuse|fs129}}<ref>'''Halo: First Strike''', ''pages 243-245''</ref>

Her involvement with the SPARTAN-II program, then codenamed "ORION Project Generation II", was born out of her own initiative, although ONI had long intended to recruit her for the task. Improving upon [[Elias Carver|Dr. Elias Carver]]'s projections for predicted colonial aggression, she privately ran over 1,400 simulations with varied parameters, always coming to the conclusion that the Outer Colonies would go into all-out war against the Inner Colonies and Earth within a short span of time. If the UNSC did not act, this would mean a minimum of thirty years of open war and billions of casualties, while the worst-case scenario was indefinite conflict and the potential collapse of human civilization. Viewing it as her personal responsibility to prevent this scenario from coming to pass, she presented her results to [[Michael Stanforth|Vice Admiral Stanforth]], then-head of ONI Section III, only to find that the UNSC had already come to the same conclusions with their own projections. As it turned out, ONI had been monitoring her for years, but they had waited for her to come up with the numbers on her own, knowing that she could not be convinced to work for them otherwise. Although she was distrustful of ONI, she agreed to work for them on the program out of her personal commitment to humanity's cause.{{Ref/Reuse|HJ12410}} The nuclear bombing of the [[Haven arcology]] by the [[Freedom and Liberation Party]] further reinforced her determination.{{Ref/Reuse|HJ22311}}

At the conceptual phase of the SPARTAN-II project, Halsey evidently failed to fully understand its moral implications; she was constantly revolted upon seeing her work in practice, and the notion of "sacrificing the few to save the many" rarely worked to soothe her conscience.<ref>'''Dr. Halsey's personal journal''', ''December 24, 2517''</ref> While she attempted to maintain a professional distance to the SPARTAN-II candidates, she could never bring herself to view them as mere test subjects and always addressed them by their first names.<ref>'''Halo: The Fall of Reach''', ''pages 26, 54''</ref> She held considerable respect for the Spartans and easily recognized them through subtle habits in their postures even with their armor on, which seemed to greatly annoy them.<ref>'''Halo: First Strike''', ''pages 120-121''</ref> In turn, the Spartans greatly respected Dr. Halsey, (with [[Jorge-052|one]] stating that he had been ''"All hers half [his] life"''),<ref>'''Halo: Reach''', campaign level ''[[ONI: Sword Base]]''</ref> and would follow her orders and suggestions in the absence of those from a superior officer.<ref>'''Halo: First Strike''', ''pages 123-124''</ref> The doctor is also privy to many of the recruits' secrets, having taught several to them as children, such as the ''[[Oly Oly Oxen Free]]'' security tune.<ref name="thunk">'''Halo: First Strike''', ''page 119''</ref> Despite her admiration of the Spartans, Halsey always kept these feelings to herself so as to not make them feel excluded due to the special treatment they get from most other humans.{{Ref/Reuse|fs123}}

Despite ONI's intentions to continue with the SPARTAN-II program, Dr. Halsey began having difficulty finding a suitably large number of candidates that fit her genetic and age profiles. Additionally, most of her budget was now being used to maintain the MJOLNIR armor in service. Eventually, ONI discontinued the SPARTAN-II program, reassigned most of its personnel to other projects (such as the [[SPARTAN-III program]], held secret from Halsey), relocated Halsey from her former workplace at [[Camp Hathcock]] to [[CASTLE Base]],{{Ref/Reuse|journal}} and cut off her access to classified material. ONI's reticence vanished, her budget mushroomed overnight, and she was offered a corner office in [[Olympic Tower]] in [[New Alexandria (location)|New Alexandria]]. However, Halsey decided to remain in CASTLE as a means of revenge against ONI, which would now have to spend half the day going through security checks.<ref name="tfor castle">'''Halo: The Fall of Reach''', '''2010''', ''pages 261-262''</ref> Halsey was stationed primarily on the planet [[Reach]] throughout her decades of work for ONI. By [[2551]], she lived in the community of [[Csongrád]], near CASTLE Base.{{Ref/Reuse|DD3}} Aside from her continued work on the SPARTAN-II and MJOLNIR projects, Halsey made huge contributions to many other ONI Section III projects, including the creation and deployment of AI constructs. She supervised the creation of the template for third-generation [[smart AI]]s,{{Ref/Reuse|HFS13}} the first ones of which became operational in [[2521]].{{Ref/Reuse|journal}}

The 'recruited' children were replaced with [[flash cloning|flash clones]], all of whom died due to various neurological and physiological diseases that were the natural side effects of making an entire human flash clone. In the early stages of the program, Halsey attempted to cover up the program's use of flash clones, both by withholding information from [[Admiral]] [[Margaret Parangosky]] and by using one of her AIs to cover fiscal evidence;<ref>'''Halo: Glasslands''', ''page 345''</ref>{{Ref/Note|Halsey's attempt to hide the cloning aspect of the program would have had to have occurred in its conceptual phase, as it would have been impossible to cover up when the cloning was put into practice; even if Halsey did manage to hide the data involving the funding, numerous ONI operatives and scientists were involved in the replacement operation and Halsey was not in a position to keep them from relaying the information to Parangosky. In addition, with ONI constantly monitoring the progress of the program, Halsey would have had no way to keep such a large-scale operation secret in the long term.}} Parangosky eventually discovered the cloning scheme, which would contribute to Halsey's arrest by ONI decades later. With the assistance of [[Chief Petty Officer]] [[Franklin Mendez]] and the AI [[Déjà]], she proceeded to train the Spartans. She supervised their augmentation procedures, combat training, and education, and studied the effects of the Spartan lifestyle on the children. She kept in close contact with them all throughout their lifetimes, from her base under Reach. To the minor annoyance of the Spartans, Dr. Halsey was capable of identifying them even underneath heavy combat gear or their MJOLNIR armor, and used their first names to prove this time and again.

[[File:Halsey John Wakes Up.png|thumb|left|230px|"Your mother is gone. Everything you know is gone. Now get up. There are things you have to do."]]
Due to her burdened conscience, Halsey was consistently at odds with ONI Section Three over the course of the SPARTAN-II program. She was irritated by the aloof demeanor exhibited by most ONI personnel toward the moral considerations of the program as well as their constant underestimation of the Spartan candidates, whom she always held in high regard.<ref>'''Dr. Halsey's personal journal''', ''September 23, 2517''</ref><ref name="apr1">'''Dr. Halsey's personal journal''', ''April 1, 2525''</ref> ONI also had little patience for hesitation or delays in what they viewed as their prize project, and often compelled Halsey to implement easier and more straightforward—and often also more unethical—solutions, while Halsey tried to do her best to ensure the safety of the candidates,<ref name="for29">'''Halo: The Fall of Reach''', ''page 29''</ref> despite knowing that she could not save them all. When an ONI representative labeled the Spartan washouts as "acceptable losses", Halsey did not view any of them as acceptable.<ref>'''Halo: The Fall of Reach''', ''page 31''</ref> Even at the onset of the augmentation procedures, which she knew would kill or cripple a large portion of the candidates, she was considering that they should take more time to test the chemicals before applying them. However, [[Déjà]] pointed out that if she proceeded too slowly and ONI detected a delay, they might replace Halsey with someone less concerned with ethics—and most likely someone less qualified as well, prompting Halsey to stay on board with the project for the sake of the candidates' safety.<ref>'''Halo: The Fall of Reach''', ''page 58''</ref> After a number of the SPARTAN-II candidates "washed out" in the augmentations, Halsey had their bodies frozen in cryostasis with no autopsies performed, hoping to find solutions to resuscitate them in time. She guessed that the ONI personnel reporting on the project's progress to the upper echelons of ONI would respond to her apparent unwillingness to let go with their characteristic detachment.{{Ref/Reuse|apr1}}

By the time she was rescued from Reach by ''Ascendant Justice'', she simply wanted to save as many lives as she could, believing that the war was not one that the UNSC could possibly win. She knew that "her own" Spartans, the Spartan-IIs, could not be persuaded to turn from the war. However, she believed the Spartan-IIIs may not yet have been fully determined to win the war and she set out to try and weaken their resolve to fight.<ref>'''Halo: Ghosts of Onyx''', ''page 342''</ref> Although she was worried about Ackerson co-opting her work on the Spartan augmentations potentially ending in disaster,{{Ref/Reuse|journal}} Halsey respected the Spartan-IIIs themselves and felt responsible for them.<ref>'''Halo: Ghosts of Onyx''', ''pages 173-178''</ref> She believed that the [[Spartan-IV]]s were incapable of being ''true'' Spartans due to their nature as adult volunteers and perceived lack of professionalism. Nonetheless, she did imply that some, (namely [[Gabriel Thorne]]), came closer to her ideals than others.{{Ref/Reuse|dhand}}
{{Clear}}
At some point, Halsey gave a eulogy for [[SPARTAN-B312]], in which she commended the Spartan's courage and sacrifice. She noted that Noble Six's choice to remain behind in Asźod allowed humanity to discover the Halos, ultimately leading to victory against the Covenant.<ref>'''Halo: Reach''', campaign level ''[[Lone Wolf]]''</ref>

===Reputation===
[[File:FoR - Ackerson n Halsey.png|thumb|250px|Halsey and her rival, Colonel James Ackerson.]]
{{Quote|no=two
|1=Sarah Palmer
|q1=[[MJOLNIR Powered Assault Armor|This armor]] — [[SPARTAN programs|this job]] — has been soiled because of you!
|2=Catherine Halsey
|q2=Soiled? I'm the only reason that armor even exists! You can't have it both ways, Commander. Unless, of course, you find the perfect scapegoat. Then spend years rewriting history. Which brings us full circle, back to your master, [[Serin Osman|Osman]].
|3=Catherine Halsey argues with [[Sarah Palmer]] about how ONI has blamed all their war crimes on her.
}}

Halsey's projects and the results they yielded gained her widespread acclaim and sympathies among many high-ranking members of the UNSC military, such as [[Admiral]] [[Michael Stanforth|Stanforth]], her most powerful ally within ONI, and [[Fleet Admiral]] [[Terrence Hood|Hood]], who deeply respected Halsey and her Spartans who had saved his own life twice, to the extent that he verbally rebuked Colonel Ackerson for detracting the Spartan-IIs.<ref name="hood">'''Halo: First Strike''', ''page 104'' (2003)</ref> However, she also garnered a number of competitors and opponents over the decades. The most notable of her rivals was [[Colonel]] [[James Ackerson|Ackerson]], who constantly tried to spy on her and co-opted her work while attempting to sabotage the SPARTAN-II program. Her former student [[Ellen Anders]] also resented Halsey, saying "She hated me and I hated her."<ref>'''[[Halo Wars]]''' ''manual, character profiles''</ref> ONI Commander-in-Chief, [[Admiral]] [[Margaret Parangosky]], was resentful of Halsey, perceiving the doctor's aversion for control and her general lack of loyalty to ONI as a threat. The Admiral only tolerated Halsey because she was so crucial to the war effort,<ref>'''Halo: Ghosts of Onyx''', ''page 48''</ref> but had her detained immediately after the end of the war. Parangosky's antipathy for Halsey was passed on to [[Serin Osman]], a Spartan-II washout whom the Admiral specifically indoctrinated and groomed to become her successor to secure her personal legacy within ONI, and ultimately culminated in Osman ordering Halsey's assassination after the Covenant abducted the doctor during the [[Requiem Campaign]]. Parangosky's, and later Osman's, AI attaché [[Black-Box]] also had an intense dislike of Halsey. This was, at least partly, passed on from his brain donor, [[Graham Alban|Dr. Graham Alban]], who worked with Halsey on the SPARTAN-II program and eventually committed suicide over his guilt. Both Alban and BB doubted the sincerity of Halsey's doubts about the ethics of her work and viewed her as genuinely amoral.<ref>'''Halo: Mortal Dictata''', ''pages 490-492''</ref>

Many of those unfamiliar with the internal dynamics of ONI and the SPARTAN-II program have come to interpret Halsey and her work in a highly negative light. Despite the predominant role of ONI and the UNSC Naval leadership in the conception and execution of the SPARTAN-II program, Dr. Halsey is often perceived as the sole individual responsible, due to her conspicuous position as the project head.<ref>'''Halo: Glasslands''', ''page 178''</ref> Taking advantage of this, ONI prefers to attribute some of the more controversial aspects of the project to their alleged lack of sufficient oversight.<ref>[http://www.neogaf.com/forum/showpost.php?p=96218485&postcount=40 '''NeoGaf:''' ''Was Dr. Halsey justified, ultimately, in creating the Spartan-II program in Halo? — View Single Post''] ([[Frank O'Connor]]: ''"Other even less savory characters are trying to harm her legacy to boost their own careers. And they're doing it by illuminating her prior actions in an ugly way."'')</ref> [[Black-Box]] even privately acknowledges to Serin Osman that the main reason for Halsey's fall from grace is to conceal or minimize the responsibility of the many others who participated in the project.<ref>'''Halo: Mortal Dictata'''</ref>  Although she was responsible for much of the program's scientific basis and harbored no illusions otherwise, Halsey was under ONI's constant supervision and was even repeatedly pressured by Section III to use more inhumane means for faster results.{{Ref/Reuse|for29}} Many have also interpreted her primary motivation as a supposed perverse scientific curiosity, ignoring—or unaware of—her sincere determination to prevent further excessive bloodshed in the Insurrection and her initial naiveté in failing to grasp the full moral ramifications of her work until witnessing it in practice.{{Ref/Reuse|HJ12410}}

[[File:Spops HalseyMarines.jpg|thumb|left|275px|Two Marines escort a handcuffed Halsey aboard UNSC ''Infinity''.]]
Such views often have their basis on information provided by the Office of Naval Intelligence, which has frequently used highly selective or outright false information to shift the blame for some of ONI's more questionable decisions (that she could be reasonably connected to) on Halsey alone. While she was publicly declared to have died on Reach,{{Ref/Reuse|glass341}} she would be branded as a dangerous war criminal in the eyes of any UNSC personnel she would come in contact with, such as the crew of the {{UNSCShip|Infinity}}. This campaign was headed by Admiral Parangosky, who had sought to place the doctor under tighter control for decades; Parangosky's policies were carried on to her heir, Serin Osman, seemingly unchanged.<ref>'''Halo: Glasslands''', ''page 82''</ref><ref>'''Halo: Glasslands''', ''pages 109-110''</ref> [[Musa-096]] also demonstrated resentment toward Halsey due to the questionable ethics of the SPARTAN-II program.<ref>'''[[Halo: Initiation]]''', ''[[Halo: Initiation Issue 1|Issue 1]]''</ref> While working with [[Kilo-Five]], [[Naomi-010]] also adopted a less sympathetic view of Halsey. Some of the [[SPARTAN-IV program|Spartan-IVs]] have also accepted this perspective on Halsey, particularly [[Sarah Palmer]], who regards the doctor with a particular contempt (though this may be due to Halsey's own open disdain for the SPARTAN-IV program); [[Gabriel Thorne]], on the other hand, was less quick to judge Halsey and sought to uncover the reasons behind her decisions rather than condemning her based on the official story alone.{{Ref/Reuse|dhand}}

[[Franklin Mendez|CPO Franklin Mendez]], the chief instructor for the Spartan-IIs and later the Spartan-IIIs, was on amicable terms with Halsey at the time of their involvement with the SPARTAN-II program. After being reunited with Halsey on Onyx, however, Mendez began to reflect on his own past and, still in denial about his own major part in ONI's morally questionable projects, he quickly became disillusioned with the doctor. The two clashed verbally several times while trapped in the [[Trevelyan|shield world]], with Mendez attempting to project his own guilt on Halsey by delivering lengthy harangues impugning her perceived faults and her work on the SPARTAN-II project.<ref>'''Halo: Glasslands''', ''pages 269-271,  331-334''</ref>

The [[The Assembly|Assembly]] took note of Halsey's work early on and concluded that she would be instrumental in initiating the course of events leading up to their own elusive goals. Additionally, they speculated that her supposed ruthlessness may have been the result of an undiagnosed or deliberately obfuscated chemical imbalance.<ref>'''[[Halo: Reach]]''', ''[[Data pads|Data pad 7]]''</ref>
{{Clear}}

===Personal life and relationships===
Halsey is a generally asocial person, extremely devoted to her work and personal goals, and rarely partakes in any social activities, apart from her occasional attendance in academic and military social gatherings despite her dislike of such events.{{Ref/Reuse|HJ12410}}{{Ref/Reuse|fs225}} Though she had distanced herself from most of her friends from her youth, she would often browse through casualty lists within the [[UNSC subnet]], finding the majority of them dead by the final years of the war.<ref>'''Dr. Halsey's personal journal''', ''September 5, 2547''</ref> She remained rather indifferent to her parents' deaths when Endymion was glassed, as she had not seen them in years and had grown aloof from them.<ref>'''Halo: Glasslands''', ''page 267''</ref> She prefers the company of AIs and admires their complexity in comparison to humans despite being angered at being mentally defeated by them.<ref name="fs129">'''Halo: First Strike''', ''page 129''</ref>

Nevertheless, she remained particularly close to a few people, even if she rarely saw them. When listing her most important relationships and connections in her journal, she mentioned [[Michael Stanforth|"the Vice Admiral"]], [[Franklin Mendez|Mendez]], [[:Category:Spartan-IIs|her Spartans]], [[Alizée]], [[Kalmiya]] and [[Jorjet]], as well as [[Jacob Keyes|Jacob]] and [[Miranda Keyes]].{{Ref/Reuse|journal}}

====Jacob Keyes====
[[File:Halseykeyes.png|250px|thumb|Jacob Keyes accompanies Dr. Halsey.]]
During her survey travels for the SPARTAN-II candidates, Halsey was required to be supervised by a military official, an order she resented. She ended up choosing then-[[Lieutenant, Junior Grade]] [[Jacob Keyes]]. Halsey had examined his files and found he had refused to testify against one of his instructors despite the teacher's error causing the deaths of 14 students. From this Halsey deduced that Keyes could be trusted to keep a secret, a useful trait in her unethical mission. The two were initially aloof to each other aboard the ''Han'', especially since Keyes did not initially know the purpose of their mission. He eventually realized it, though, and discussed with Halsey about the implications of her project and her decision to tell the child [[Soren-066|Soren]] the truth. By the time they parted after two months working together, Keyes and Halsey were on much more amicable terms, to the point that Halsey began sketching him frequently in her journal and even referred to him as "my lieutenant". For his safety and in thanks, Keyes was reassigned but given a full [[Lieutenant (UNSC)|lieutenant]] commission, at Halsey's request.

In November [[2524]] the two were reunited while attending a conference at the [[University of Calippus]], and the two conceived a child, Miranda. While she initially raised her daughter on Reach for several years, Halsey's work impeded her from being able to care for Miranda, and Jacob ended up raising her instead. The two did not see each other again until August 12, 2552, a moment that Halsey had both hoped for but dreaded. Keyes still remained a gentleman to her, and they spoke at length on the topics of Miranda, the Spartans, and his "[[Keyes Loop]]", and his assigning to [[Operation: RED FLAG|RED FLAG]], also at Halsey's request. It was the last time the two saw each other before Keyes's death at [[Installation 04]].
{{Clear}}

====Miranda Keyes====
[[File:Young Miranda.png|thumb|left|250px|Halsey's sketches of a young Miranda.]]
In [[2525]], Catherine gave birth to [[Miranda Keyes|Miranda Halsey]] and raised her for a few years until July 12, [[2531]] when Miranda's father agreed to take her in, raising her on [[Luna]]. Halsey would later have a falling-out with Miranda, who would later change her legal name to her father's and refuse to speak to Halsey for several years. Nonetheless, Halsey cared for her daughter and attempted to dissuade her from following her father's footsteps and joining the military, to no avail. Hoping to keep Miranda safe, Halsey used her influence within the UNSC to have her assigned to a remote post aboard the science vessel {{UNSCShip|Hilbert}}; however, Miranda and the ''Hilbert'' would play a crucial role in battle, and she was subsequently assigned to various front-line posts. Though Miranda eventually invited Halsey to her promotion ceremony in [[2550]], Halsey chose not to attend.{{Ref/Reuse|journal}} Perhaps out of denial of her absence from Miranda's life, Halsey rarely referred to her daughter by name in her journal, or would mention Miranda while avoiding the detail that they were related. However, Miranda still remained on her mind during their estrangement, and Halsey kept a memento of Miranda's victory and promotion at the [[Battle of Gamma Pavonis VII]]. She also had a photo of Miranda in her office under [[CASTLE Base]].

After her arrest by ONI in 2553, Halsey was informed that Miranda Keyes was dead, having been killed by the [[Prophet of Truth]] at the [[Battle of the Citadel]]. [[Black-Box]] later oversaw Halsey crying and whispering her daughter's name.<ref>'''Halo: The Thursday War''', ''page 267''</ref>
{{Clear}}

====John-117====
[[File:Halo TFoR HalseyJohnhelmet.jpg|thumb|300px|John, at 14 years of age, having his original Mjolnir helmet put on by Dr. Halsey.]]
{{quote|This boy could be more useful to the UNSC than a fleet of [[UNSC destroyer|destroyer]]s, a thousand [[Lieutenant, Junior Grade|Junior Grade Lieutenants]] -- or even ''me''. In the end, the child may be the only thing that makes ''any'' difference.|Halsey speaking to [[Jacob Keyes|Lt. Jr. Grade Jacob Keyes]], referring to John-117.}}
Halsey had a unique relationship with [[John-117]], compared to the other Spartans. John was the first subject for the Spartan program that she observed, and during then she noted his determination, physical skill, and luck in answering correctly. Halsey told Cortana she considers him the luckiest and best of the Spartans and apparently also finds him attractive on a subconscious level, given her embarrassed reaction to Cortana's comments.<ref>'''Halo: The Fall of Reach''', ''page 236'' (2001)</ref> The doctor was responsible for John's first promotion to Squad Leader as a result of her acknowledging his leadership skills and suggesting it to Mendez. She also had John's full trust, him always doing his best to never undermine her authority.

After escaping from Reach, Halsey decided to test her favorite Spartan's sense of ethics by handing over two sets of data: one concerning [[Avery Johnson]] and how his [[Boren's Syndrome]] supposedly made him immune to the [[Flood]], and the other omitting those details. She ensured that John knew that if the first set was handed over to ONI, Johnson would likely be killed and dissected in order to find a cure to the Flood infection. She estimated that there is a billion to one shot that they could have replicated Johnson's condition, but conversely ONI would do it to save humanity from a greater foe.<ref>'''Halo: First Strike''', ''pages 242-246''</ref> At first, John chose to sacrifice Johnson in order to try and save millions of people out of his duty to protect all of humanity. However, he later reconsidered and eventually destroyed the Johnson data due in part to the sacrifice of [[Vice Admiral]] [[Danforth Whitcomb]] and [[Lieutenant]] [[Elias Haverson]], believing that one man could make a difference as opposed to sacrificing him for the greater good.<ref>'''Halo: First Strike''', ''pages 329-336''</ref>  John's faith in him was fully realized a mere two months later, when Johnson became key in forming an alliance between humans and [[Sangheili]] following the [[Great Schism]] and outbreak of the [[Flood]] in [[2552#November|November 2552]].

Later, despite John going MIA after the events on Installation 08, Halsey was sure that he was still alive,{{Ref/Reuse|Prologue}} and was furious when she found out that the ''Infinity''{{'}}s crew had kept the news of his return secret from her.{{Ref/Reuse|invasion}} John restored her faith that humanity could win against impossible odds, since he had brought about the end of the Human-Covenant war despite her belief in its latter months that it was unwinnable.

In [[2559#October|October 2559]], following [[Operation: WOLFE]], she is visibly distressed by the bad state of Blue Team and John is forced to steady her. Halsey calls the Spartans her greatest achievement and asks if John understands that, but he asks if she's alright in return which she evasively responds to. Seeing Halsey so upset by their return in such a bad state causes John to consider her reaction, considering that she had sent them on the mission in the first place and she had seen Spartans return in as bad a state or not return at all. John wonders if, based on some of the things that she has said, Halsey regrets some of her work or at least some of the things that had been necessary to create the Spartans. However, despite knowing the extent to which Halsey had gone, John is glad that she had done it and he and his fellow Spartan-II's are proud of what they had become and what they had done to save humanity. While John wants to tell her that, he is unable to find the words to express himself adequately to her.{{Ref/Reuse|SoR}}

====Cortana====
[[File:HaloReach - Finale.png|thumb|left|250px|Halsey facing Cortana, her literal brainchild.]]
[[Cortana]] was an AI created by Halsey herself, and unique that she was "born" from a cloned brain rather than that of a deceased donor. Halsey considered her to be much like herself when she was just out of college, "so wonderful and naive and eager to learn"{{Ref/Reuse|journal}} and constantly eager to state her knowledge to anyone listening.<ref>'''Halo: The Fall of Reach''', ''page 218''</ref> Her appearance also reminded Halsey a little bit of Miranda. Like all her AIs, Halsey implanted a viral termination code in Cortana, but she suspected, and seemed amused by, the possibility that Cortana had already discovered it and removed it.

Halsey would treat Cortana as an equal, especially in the missions regarding her, letting Cortana chose who would be her couriers. For Operation: RED FLAG, Cortana chose the ''Pillar of Autumn'' and John-117 to escort her. When her fragment had to be delivered to Asźod, Cortana chose [[SPARTAN-B312]] of NOBLE Team to be the one to defend her. Halsey agreed with each of her choices, and wondered if her preferences were what subconsciously influenced Cortana, or if it were simply that "great minds do think alike."
{{Clear}}

====Jul 'Mdama====
[[File:H4SO Ep8 Halsey-and-Mdama.jpg|thumb|250px|Covenant leader Jul 'Mdama and Doctor Catherine Halsey.]]
{{Quote|This human is more trouble than she is worth.|Jul 'Mdama, remarking on Halsey's lack of apparent progress deciphering the signals between Cortana and the Guardians.<ref>'''Halo 5: Guardians''', ''campaign level [[Osiris (level)|Osiris]]''</ref>}}

While Halsey colluded voluntarily with 'Mdama's schemes to acquire the other half of the Janus Key, she was only ever using him for his resources, hoping to claim the Librarian's "gift" for herself. She offered strategic advice, recommending the colony of [[Oban]] as a target, and encouraged Jul to drop his show of piety between the two of them,<ref>'''Halo: Escalation''', ''issue #13''</ref> and was even trusted enough by Jul to go out into the field with a [[Zealot]] escort during the battle of Aktis IV.<ref>'''Halo: Escalation''', ''issue #15''</ref> Nevertheless, when both the Covenant and the UNSC finally reached the Absolute Record, Halsey was quick to turn on 'Mdama, turning the Installation's Sentinels on him and his men.<ref>'''Halo: Escalation''', ''issue #23''</ref> While Jul recovered Halsey from the Installation as they escaped its self-destruction, not realising her betrayal, the Covenant leader began to realise that was "more trouble than she is worth."<ref>'''Halo: Escalation''', ''issue #24''</ref> During the Covenant's occupation of Kamchatka, Halsey finally took the final step in dissolving their alliance, calling in [[Fireteam Osiris|a Spartan team]] to extract her in exchange for crucial information on the Guardians. This resulted in 'Mdama's death before her, an event that went unremarked upon by Halsey.<ref>'''Halo 5: Guardians,''' ''Osiris''</ref>
{{Clear}}

==Skills and abilities==
At a young age Halsey was considered a prodigy.{{Ref/Reuse|WaypointCatherineHalsey}} She is also a noted polymath, her expertise and knowledge making her a professional in multiple fields. She has formal degrees as a medical doctor and computer scientist,{{Ref/Reuse|alph}}{{Ref/Reuse|HFS13}} and she has demonstrated remarkable skill in AI development, quantum theory and slipspace-related phenomena, the engineering of military equipment such as power armor and related technologies, as well as [[xenoarchaeology|xenoarchaeological]] research into Forerunner technology and the translation of [[Forerunner symbols]]. Because of her extensive contributions to AI development, Halsey is capable of holding her own against [[smart AI]]s,{{Ref/Reuse|HFS13}}{{Ref/Reuse|invasion}} using her expertise to exploit secret programming backdoors or philosophical puzzles to control or manipulate constructs as advanced as fifth-generation smart AI.<ref>'''Halo: Ghosts of Onyx''', ''pages 178-179''</ref> She types at a rate of 140 words per minute.<ref>'''Halo: Ghosts of Onyx''', ''page 177''</ref> Her skills as an artist, as demonstrated by the plethora of drawings in her journal, have also been noted.<ref>'''Halo: Glasslands''', ''page 433''</ref> Catherine Halsey was also able to perfectly understand [[Jul 'Mdama]], indicating that she has some knowledge of the [[Sangheili (language)|Sangheili language]].{{Ref/Reuse|Spops8}}

According to the [[Librarian]], a [[geas]] she planted into the human genome 100,000 years earlier encouraged the development of many of the technologies Halsey created in order to prepare humanity for a major threat they would be forced to confront as [[Reclaimer]]s.<ref>'''Halo 4''', campaign level ''[[Reclaimer (level)|Reclaimer]]''</ref> The Librarian's stored essence on Requiem placed a particular responsibility on Halsey, giving her the [[Janus Key]] to advance humanity.{{Ref/Reuse|s1key}}

==Attire and personal effects==
[[File:HalseyHaloReach.png|thumb|250px|Halsey wearing a parka in her SWORD Base archaeological dig.]]
Because she is most often occupied with her work, Halsey typically wears a lab coat. On Reach she was often seen wearing a skirt although she has later shown to don the standard ONI scientist utility clothes with a blue tunic and pants under her lab coat. When outdoors in Reach's Highlands and in her SWORD base archaeological site she often wore a heavy parka because of the cold.<ref name="journal">Halsey's Journal</ref> She has a set of antique<ref>'''Halo: First Strike''', ''page 121''</ref> bifocal{{Ref/Reuse|thunk}} glasses which feature a variety of functions, including a [[heads-up display]], a retinal and brain pattern scanner,<ref>'''Halo: The Fall of Reach''', ''page 56''</ref> as well as automatic polarization.{{Ref/Reuse|goo345}} The frames contain tiny projectors which can beam classified data directly onto her retina.<ref>'''Halo: The Fall of Reach''', ''page 231''</ref> However, she seems to have largely abandoned her use of the glasses in the post-war era.

She typically carries a personal [[Portable computer|laptop]] on her as well as a purse, the latter containing a [[data pad]], a pocket archive, a change of clothes, self-amalgamating tape, a pocket saw, a solar power pack, medications, a folding knife, her mother's antique Patek Philippe luxury watch, as well as coffee for "emergencies".<ref>'''Halo: Glasslands''', ''page 262''</ref> Halsey had several personal AIs, including [[Jerrod]], who could run on her laptop, and [[Kalmiya]], who served as her assistant on Reach.<ref>'''Halo: First Strike''', ''page 126''</ref> Halsey had a snowglobe on her desk in her CASTLE Base office, containing a three-centimeter-tall representation of the Matterhorn being scaled by a tiny Swiss climber.<ref>'''Halo: First Strike''', ''page 191''</ref>

Halsey kept [[Dr. Halsey's personal journal|a journal]] with her ever since she was eighteen, purchased from a shop on Reach. She used the journal as a medium through which to express her thoughts and concerns, draw sketches, and map out important research notes for approximately forty-two years. It was not Halsey's only journal, since she had a second one for note-taking and also had an encrypted audio journal on her computer, though she sometimes erased its entries soon after recording them.<ref>'''Halo: Fall of Reach''' - ''Bootcamp Issue 1''</ref> Halsey frequently left her first journal lying around buried under papers, and procrastinated on adding some security measures to it to prevent it from being stolen.<ref>'''Dr. Halsey's personal journal''', ''March 18, 2543''</ref> This absent-mindedness eventually backfired on her when she forgot the journal during her escape from [[SWORD Base]]. The journal was later recovered by ONI in [[2553]], and used as evidence to condemn her.
==Non-canon and dubious canon appearances==
{{Notice/Silver|category=no}}
===Silver Timeline===
{{Main|Catherine Halsey/Silver}}
{{Expand-section}}

==Production notes==
{{Linkbox|quote=yes|gallery=yes}}
*In ''[[Halo: Reach]]'', ''[[Halo 4]]'', ''[[Halo 5: Guardians]]'', and ''[[Halo Infinite]]'', Dr. Halsey is voiced by [[Jen Taylor]], who also voices Cortana, reinforcing the connection between the two characters. This is mirrored in ''Halo Legends'' (which predates the three games), in which [[Shelley Calene-Black]] voices both Halsey and Cortana.<ref>'''''Halo: Legends''''' credits</ref> [https://www.imdb.com/name/nm0001523/?ref_=ttfc_fc_cl_t2 Natascha McElhone] will plays Halsey in ''[[Halo: The Television Series]]'' and provides the motion capture for Cortana, who is again voiced by Jen Taylor.
*A number of Dr. Halsey's statements are echoed by similar statements by Cortana in the ''Halo'' games. In ''[[Halo: The Fall of Reach]]'', when John-117 explains his plan to board the [[Unrelenting|Covenant ship]] near [[Chi Ceti IV]], Halsey states, ''"One slight error in your trajectory, and you could miss by kilometers"'', to which John replies, ''"I don't miss, ma'am."''<ref>'''Halo: The Fall of Reach''', '' page 120'' (2001)</ref> A strikingly similar exchange occurs in ''[[Halo 2]]'', with Cortana asking, ''"What if you miss?"'' and John responding, ''"I won't"''. Many of Cortana's lines during the [[Cortana moments and Gravemind moments|Cortana moments]] in ''Halo 3'' are direct quotes or slight paraphrases of Halsey's statements to the Spartans in ''Halo: The Fall of Reach''. In ''[[The Package (animated short)|The Package]]'', Halsey tells John-117 that she slept well, ''"No thanks to their driving,"'' which is echoed in ''Halo: Combat Evolved'' when he tells Cortana he slept well ''"... no thanks to [her] driving"''. She also tells John, ''"Don't make a girl a promise if you know you can't keep it,"'' which Cortana would tell him in ''Halo 2''.
*In ''Halo Legends'', Halsey's appearance was portrayed with a great deal of artistic license. In ''The Package'', at which point she is aged fifty-two, she is depicted as a young woman with short, blonde hair and no glasses. Her appearance in ''Homecoming'' however, is closer to her description from the books, though that short also portrays her as blonde. In the developer commentary for ''Homecoming'' [[Frank O'Connor]] states, "''People tend to think of her as older than she's portrayed... and part of that was simply—you know—it's anime, and they want everyone to be attractive and young. I mean, that's one of the hallmarks anime... I think that IG took the safer of the two routes and sort of disguised her appearance and disguised her age by having it literally obscured by her hair and her glasses and to a certain extent her uniform.''" In ''The Package'' commentary he explains, "''She was definitely one of those back-and-forth conversations [with Casio Entertainment]; 'Can you make her older? Can you make her older?' And eventually we got to this compromise... I think if we were casting a real-life actress we'd cast someone a lot older, but in anime the context is fine and it works.'"''
*''Halo: First Strike'' states that Halsey never refers to the Spartan-IIs by their numerical designations, using only their names. In ''Homecoming'', however, she refers to Daisy-023 as ''"Twenty-Three"'' when trying to convince her to return to the SPARTAN-II program.
*[[Dr. Halsey's personal journal]] is included in ''[[Halo: Reach]]''<nowiki>'</nowiki>s [[Halo: Reach Limited Edition|Limited]] and [[Halo: Reach Legendary Edition|Legendary Editions]]. The journal was mostly written by [[Eric Nylund]] in conjunction with Bungie and 343 Industries, with [[Lorraine McLees]] serving as art director. Included with the journal is Halsey's ONI badge. Scanning the barcode on it with a barcode reader translates it as "HALSEY". Holding the badge under a black light reveals her face over the ONI emblem.<ref>[http://www.ign.com/videos/2013/02/27/secret-halo-reach-blacklight-easter-egg '''IGN''': ''Secret Halo: Reach Blacklight Easter Egg'']</ref>
*According to lead writer [[Brian Reed]], the object of Dr. Halsey's revenge at the end of ''Spartan Ops'' was originally clear-cut — Commander Palmer and the crew of ''Infinity''. However, this plot point was considered too blatant and out of character. To better depict Halsey's signature "double talk", this was changed to the less obvious presentation used in the final draft. During [http://blogs.halowaypoint.com/Headlines/post/2013/03/04/Spartan-Ops-Episode-Review.aspx his review of Season 1], Reed suggested that Halsey's grudge may be against Commander Palmer specifically, the UNSC as a whole, or "everyone" in general. However, he implied that she was actually making a veiled threat toward Jul 'Mdama. Furthermore, Halsey was not originally planned to lose her arm in ''[[S1/Exodus|Exodus]]''. The writers later decided to remove her arm to add a sense of ambiguity as to whom Halsey wanted revenge on.<ref>[http://blogs.halowaypoint.com/Headlines/post/2013/02/27/The-Halo-Bulletin-22713.aspx '''Waypoint''': ''The Halo Bulletin: 02.27.13'']</ref>
*Catherine Halsey is also the name of a character in the 1943 novel ''The Fountainhead'' by Ayn Rand. In the novel Halsey progresses into becoming an altruist, thinking of nothing other than the greater good of the majority. In this sense, she is an opposite of the Halsey of the ''Halo'' universe. Dr. Halsey begins by sacrificing the Spartans to buy the UNSC more time, but then changes her mind and does everything she can to save the Spartans, regardless of what happens to the rest of humanity.
* Early ''Halo 5'' menu concepts imply that Halsey would have been an antagonist in early drafts of the game, involving a Forerunner warship and the UNSC attempting to stop her.<ref>{{Plain|[https://www.artstation.com/artwork/armor-customization-concept-ethereal-ui '''Artstation.com''', ''Ramiro Galan'']}}</ref>

==Gallery==
<gallery>
File:HalseyHomecoming.png|Halsey in ''[[Homecoming]]''.
File:Halsey 2.jpg|Halsey overlooking [[Daisy-023]]'s Spartan augmentations.
File:Halsey Hornet.jpg|Halsey in an [[AV-14 Hornet]], informing Daisy-023 about the purpose of her flash-clone.
File:LegendsPackage - Halsey.png|A render of Catherine Halsey in ''[[The Package (animated short)|The Package]]''.
File:HLTP-DoctorHalsey-FingerStop.jpg|Halsey in ''The Package''.
File:Halsey Legends.jpg|Halsey in ''The Package''.
File:HR_HalseyFace_Concept.jpg|A concept portrait of Halsey for ''Halo: Reach''.
File:HR_Halsey_Concept_1.jpg|''Halo: Reach'' concept art.
File:HR ThreeHalseysConcept.jpg|More ''Halo: Reach'' concept art.
File:HR HalseyOutfitsConcept.jpg|More ''Halo: Reach'' concept art.
File:HR HalseySingleConcept.jpg|Concept art nearing her final design in ''Halo: Reach''.
File:HR-DoctorHalsey-ScanRender.png|Halsey in ''Halo: Reach''.
File:Halsey_Badge.jpg|Dr. Halsey's [[Office of Naval Intelligence|ONI]] security badge.
File:Halsey ID badge.png|Halsey's security badge under natural light, partial black light, and total black light.
File:Halsey_Signature.jpg|Dr. Halsey's signature.
File:Halsey_in_FoR.png|A young Halsey in ''[[Halo: Fall of Reach]]''.
File:Halsey Memory.jpg|One of [[Jacob Keyes]]' final memories of Halsey before he is assimilated into the [[proto-Gravemind]].
File:Halsey Halo 4.png|Catherine Halsey in ''Halo 4''.
File:H4 Halsey Profile.jpg|A profile of Halsey in ''Halo 4''.
File:H4-DoctorHalsey-Profile.png|A closeup of Halsey's face in ''Halo 4''.
File:H4-DoctorHalsey-ScanRender.png|Portrait of Catherine Halsey with amputated arm.
File:H4-Bio-DoctorHalsey.png|Profile sheet of Catherine Halsey.
File:Halsey Escalation.jpg|Halsey in ''[[Halo: Escalation]]''.
File:Halo Escalation 23.jpg|Halsey on the cover of ''[[Halo: Escalation#23]]''.
File:Halo Escalation 24.jpg|Halsey on the cover of ''[[Halo: Escalation#24]]''.
File:HtT-Halsey.gif|Halsey in ''[[Hunt the Signal]]''.
File:HTFOR-Halsey.png|Halsey in ''[[Halo: The Fall of Reach - The Animated Series]]''.
File:H5G-Render-Halsey.png|A render of Halsey in ''Halo 5: Guardians''.
File:HINF HoloHalseyCortana.png|A hologram of Halsey along with Cortana in ''[[Halo Infinite]]''.
File:Enc22-Halsey.png|File:Halsey in the ''[[Halo Encyclopedia (2022 edition)]]''.
</gallery>

==List of appearances==
{{col-begin}}
{{col-3}}
*''[[Halo: The Fall of Reach]]'' {{1st}}
**''[[Halo: The Fall of Reach#2010 bonus content|Adjunct]]'' {{Mo}}
*''[[Halo: The Flood]]'' {{Mo}}
*''[[Halo: First Strike]]''
*''[[i love bees]]'' {{Mo}}
*''[[Halo 2]]''
**''[[Conversations from the Universe]]'' {{Mo}}
*''[[Halo Graphic Novel]]''
**''[[Halo Graphic Novel, Page 122|Page 122]]'' {{Mo}}
*''[[Halo: Ghosts of Onyx]]''
*''[[Halo 3]]'' {{Im}}
*''[[Halo: Contact Harvest]]'' {{C|As "Charlie Hotel"}}
*''[[Halo: The Cole Protocol]]''
*''[[Halo Wars: Genesis]]'' {{Mo}}
*''[[Halo Wars]]'' {{Mo}}
*''[[Halo 3: ODST]]'' {{Mo}}
*''[[Halo Legends]]''
**''[[The Babysitter]]'' {{Mo}}
**''[[Homecoming]]''
**''[[The Package (animated short)|The Package]]''
*''[[Halo: Evolutions]]''
**''[[Pariah]]''
**''[[Human Weakness]]'' {{Mo}}
*''[[Halo: Reach]]''
**''[[Data pads]]'' {{Mo}}
**''[[Dr. Halsey's personal journal]]''
{{col-3}}
*''[[Halo: Fall of Reach]]''
**''[[Halo: Fall of Reach - Boot Camp|Boot Camp]]''
**''[[Halo: Fall of Reach - Covenant|Covenant]]''
**''[[Halo: Fall of Reach - Invasion|Invasion]]''
*''[[Halo: Glasslands]]''
*''[[Halo: Combat Evolved Anniversary]]''
**''[[Terminal (Halo: Combat Evolved Anniversary)|Terminals]]''
*''[[Halo: The Thursday War]]''
*''[[Halo 4]]''
**''[[Spartan Ops]]''
**''[[Infinity Briefing Packet]]'' {{Mo}}
*''[[Halo: Initiation]]'' {{Mo}}
*''[[Halo: Escalation]]''
*''[[Halo: Mortal Dictata]]'' {{Mo}}
*''[[Halo: New Blood]]'' {{Mo}}
*''[[Hunt the Truth]]''
**''[[Hunt the Signal]]''
*''[[Halo: Saint's Testimony]]'' {{Mo}}
*''[[Halo: The Fall of Reach - The Animated Series]]''
*''[[Halo 5: Guardians]]''
**''[[Halo 5: Guardians Limited Edition dossiers|Limited Edition dossiers]]'' {{Mo}}
*''[[Halo: Ground Command]]'' {{Mo}}
*''[[Halo Mythos]]''
*''[[Halo Fractures]]''
**''[[Lessons Learned]]'' {{Mo}}
**''[[Rossbach's World (story)|Rossbach's World]]'' {{Mo}}
{{col-3}}
*''[[Halo Wars 2]]'' {{Mo}}
*''[[Halo: Legacy of Onyx]]'' {{Mo}}
*''[[Halo: Collateral Damage]]''
*''[[Halo: Bad Blood]]''
*''[[Halo: Silent Storm]]''
*''[[Halo: Official Spartan Field Manual]]''
*''[[Discover Hope]]'' {{Mo}}
*''[[Halo: Oblivion]]''
*''[[Become]]''
**''[[Step Inside]]''
*''[[Halo: Shadows of Reach]]''
*''[[Halo Infinite: Memory Agent]]'' {{Mo}}
*''[[Halo Infinite]]''
*''[[Halo: The Television Series]]''
*''[[Halo: Sunrise on Sanghelios]]''
*''[[Halo: The Machine Breaks]]''
{{col-end}}

==Notes==
{{Ref/Notes}}

==Sources==
{{Ref/Sources|3}}

[[Category:Human characters|Halsey, Catherine]]
[[Category:Scientists|Halsey, Catherine]]
[[Category:Office of Naval Intelligence personnel|Halsey, Catherine]]
[[Category:Jul 'Mdama's Covenant members|Halsey, Catherine]]