2552

Early 2552

The Spartans of Gamma Company receive their orders.

July 17, 2552

The Battle of Sigma Octanus IV begins.

July 18, 2552

The UNSC win a victory at the Battle of Sigma Octanus IV. Commander Keyes, of the UNSC Iroquois, plays a critical role in this success. Keyes is subsequently promoted to Captain by Admiral Stanforth. Unknown to the UNSC, the Covenant place a tracker on the hull of the Iroquois. The importance of Reach to the UNSC is revealed to the Covenant when the Iroquois returns to that world.

August 12, 2552

SPARTAN-117 and Corporal Harland are debriefed by ONI at Camp Hathcock, Reach, on the events on Cote D'Azur during the Battle of Sigma Octanus IV.

August 25, 2552

Dr. Halsey and Cortana choose the UNSC Pillar of Autumn, with Keyes as her commander, for a secret mission Halsey is planning.

August 27, 2552

All but three SPARTAN-IIs gather at the FLEETCOM Military Complex on Reach, where they learn of their next mission: to acquire a Covenant vessel, navigate to the Covenant home world, and return with captured Covenant leadership.

August 29, 2552

SPARTAN-117 receives a neural interface upgrade, armor, and is introduced to Cortana.

August 30, 2552

• Cortana has ONI Colonel James Ackerson illicitly transferred to the front. This is her revenge for his attempts to eliminate both her and SPARTAN-117.
• The Covenant, despite sustaining heavy losses, win a crushing victory at the Battle of Reach. Many of the remaining SPARTAN-IIs are killed.
• The UNSC Pillar of Autumn escapes the disaster at Reach although, due to Cortana, the jump is not blind as per the Cole Protocol.
• The surviving SPARTAN-IIs on Reach are separated into two groups. One recovers Vice Admiral Whitcomb and goes into hiding at Camp Independence. The others are admitted into CASTLE Base by Dr. Halsey and receive parts of the MJOLNIR Mark V upgrade and new weapons.
• Halsey learns of Colonel Ackerson's mysterious plans that seem to involve "her" Spartans.

September 4, 2552

Lieutenant Wagner returns to Earth and reports on the evident destruction of Reach to Colonel James Ackerson, Admiral Hood, and General Strauss at an ONI facility in Sydney, Australia.

September 7, 2552

• The Time/Date Record Anomaly of Sept 23, 2552 most likely rejoins the timeline here.
• Dr. Halsey and members of Red Team discover an enigmatic shard in a Forerunner installation below CASTLE Base. They are besieged by Covenant forces who seek to possess the shard.

September 2552

The remaining Spartans, Admiral Whitcomb, Dr. Halsey, Sgt. Johnson, Lieutenant Haverson, Warrant Officer Polaski, and Corporal Locklear jump to Slipspace on board the Covenant/Human hybrid ship Gettysburg-Ascendant Justice, and discover that the shard seems to have the ability to bend both space and time.

September 12, 2552

The Gettysburg/Ascendant Justice arrives for refit and provisioning in Eridanus system and meets with the rebels under Governor Jiles. Dr. Halsey sedates Spartan 087, Kelly, and absconds with her on Governor Jiles' personal ship, the Template:ShipClass Beatrice. Before she goes, she gives the alien artifact to Corporal Locklear, with implicit instructions to destroy it.

September 13, 2552

UNSC forces aboard the Gettysburg/Ascendant Justice win a crucial victory at the Battle of the Unyielding Hierophant. SPARTAN-093 and Vice Admiral Whitcomb are killed. The survivors, now aboard the singular UNSC Gettysburg, depart for Earth to warn of the impending Covenant invasion.

September 19, 2552

• The Battle of Installation 04 begins.
• SPARTAN-117 is awoken from cryosleep and tasked with preventing Cortana's capture by the Covenant.
• The UNSC Pillar of Autumn arrives at Alpha Halo
• SPARTAN-117 and Cortana escaped the ship aboard a Bumblebee-class Lifepod who later crashed on the ring.
• The UNSC Pillar of Autumn is forced to crash land on the ring. A significant portion of her crew survives to continue the fight on the ground.

• Captain Keyes and the others in his escape pod are captured by the Covenant. Only Keyes escapes summary execution, and is taken to the Template:ShipClass Truth and Reconciliation.

September 20, 2552

• SPARTAN-117 leads a marine force to board the Truth and Reconciliation. They recover Keyes and escape aboard a Covenant dropship. Keyes orders SPARTAN-117 to find the "Silent Cartographer", a map room that will reveal the location of the Control Room. Keyes leaves to lead an assault on a Covenant weapons cache.
• Having found the map room and the pertinent information, Cortana directs a Pelican to take them to the area where the ring's Control Room is. Upon reaching the Control Room, Cortana transfers to the Control Room's computer and directs SPARTAN-117 to stop Keyes from accessing the 'weapons cache', really a Forerunner quarantine facility.
• SPARTAN-117, without Cortana, enters the facility but is unable to locate Keyes. Instead, he discovers the "Flood" and is forced to retreat. He links up with and takes command of the surviving members of Keyes' team and fight their way to the extraction point. However, the Spartan is conscripted by "Monitor" of Installation 04 and teleported away before he can be evacuated.

September 21, 2552

• The Monitor takes SPARTAN-117 to the ring's "Library" to retrieve the "Index", a device needed to activate the ring's primary weapon. Having retrieved the Index, the Monitor teleports the Spartan back to the Control Room where an irate Cortana confiscates the Index and prevents the ring from firing. SPARTAN-117 and Cortana flee a now-hostile 343 Guilty Spark and Sentinels.
• To forestall the ring from being activated manually, SPARTAN-117 disables the ring's three Pulse Generator. This is to buy time to destroy the ring by activating the auto-destruct on the Pillar of Autumn. Only Keyes neural interface can activate the ship's self-destruct, and SPARTAN-117 embarks once more to rescue the captain.
• Cortana teleports the Spartan to the Flood-overrun Covenant cruiser where Keyes is being held. Alas, the pair arrives too late to save Keyes, who has been merged into a Brain Form. SPARTAN-117 retrieves the neural interface by punching in the former-captain's head. Cortana downloads the necessary codes, and the duo returns to the Pillar of Autumn on a captured Banshee.
• 343 Guilty Spark overrides the auto-destruct codes, forcing SPARTAN-117 to manually destabilize the ship's still-functioning fusion cores. SPARTAN-117 and Cortana then escape the resulting explosion and the fragmentation of the ring aboard a Longsword.
• Sergeant Johnson, Lieutenant Haverson, Warrant Officer Polaski, Corporal Locklear also escape the destruction of the ring aboard a Pelican.
• The Battle of Installation 04 ends.

September 22, 2552

SPARTAN-117 and Cortana rendezvous with Johnson's group in Installation 04's debris field. They also recover a set of cryotubes, one which contains SPARTAN-058.

September 23, 2552

• As the Longsword and Pelican are not jump capable, the UNSC survivors assault and capture the Ascendant Justice, a Covenent warship, They then set course for Reach.
• A Time/Date Record Anomaly continues from this point in the narrative, resolved above on Sep 7, 2552.

October 19, 2552

• The High Prophet of Regret takes his private fleet to search for the other rings. This course of action is without the approval of the other high prophets.
• The survivors of the Pillar of Autumn arrive in Sol.

October 20, 2552

• SPARTAN-117 is outfitted with the MJOLNIR Mk. VI aboard Cairo Station.
• The Fleet Commander of Particular Justice is deemed a Heretic by the Covenant High Council and sentenced to death.
• SPARTAN-117 and Sergeant Johnson are decorated at a ceremony aboard Cairo Station. Captain Keyes is awarded posthumously and the decoration is entrusted to Commander Keyes.
• The First Battle of Earth begins.
• The High Prophet of Regret's fleet arrives at Earth, not expecting any human presence. The vastly outnumbered Covenant force attacks without seeking support from other Covenant forces.
• SPARTAN-117 foils a Covenant attempt to demolish Cairo Station and commandeers the Covenant bomb to destroy an assault carrier.
• The High Prophet of Regret's assault carrier breaks through the orbital defenses and initiates a ground assault on New Mombasa and the surrounding area.

• SPARTAN-117 deploys to New Mombasa in an attempt to capture the High Prophet of Regret. Before this can happen, the assault carrier initiates a slipspace jump within the city, escaping Earth and destroying the city in the process. The UNSC In Amber Clad, with SPARTAN-117 aboard, successfully pursues the carrier through slipspace.
• The First Battle of Earth ends.
• The Supreme Commander of the Fleet of Particular Justice becomes the Arbiter.

October 21, 2552

• The former Fleet Commander of Particular Justice is made the Arbiter by the High Prophets of Truth and Mercy.
• The Arbiter's destroys a heretic group and 'recovers' the Oracle.
• The Battle of Installation 05 begins.
• The UNSC In Amber Clad arrives at Delta Halo, following the High Prophet of Regret's assault carrier. SPARTAN-117, aided by ODSTs and marines, pursue the High Prophet to a Forerunner temple and assassinate him. However, orbital bombardment from the escorting fleets of the newly arrived High Charity destroys the temple. SPARTAN-117 is thrown into a lake and captured by Gravemind.
• The Arbiter is sent to Delta Halo to retrieve that installation's Index. The Arbiter is successful, but is then betrayed by Tarturus, who casts the Arbiter into the depths of the ringworld. The Arbiter is subsequently captured by Gravemind.
• The Civil War of the Covenant begins.

October 22, 2552

• Gravemind sends SPARTAN-117 and the Arbiter to secure the Index and prevent the installation from being activated. SPARTAN-117 is teleported to High Charity while the Arbiter is teleported close to the Control Room. Both are aided by the chaos of the Covenant civil war.
• SPARTAN-117 is unable to prevent the Index from leaving High Charity with Tarturus. Instead, on the advice of Cortana, the Spartan stows away aboard the Forerunner ship that is carrying the High Prophet of Truth to Earth. Cortana remains behind to ensure the destruction of Installation 05, should that become necessary.
• Cortana sends a slipspace message to Earth informing them that SPARTAN-117 is en route.
• The Arbiter reaches the Control Room but is unable to prevent Tarturus from activating the ring. With the help of humans and the Elites the Arbiter kills Tarturus. This allows Commander Keyes to physically remove the Index from the Core, temporarily interrupting the firing sequence.
• Due to the interruption, Installation 05 automatically sends a signal to all other Forerunner installations in the galaxy, activating and placing them in stand-by mode.

October 31, 2552

• The Battle of Onyx begins.
• The standby signal rouse the Sentinels of Onyx, who destroy the UNSC base on the world.
• Kurt, Mendez, and some spartans battle to survive the sentinels onslaught.

November 3, 2552

• Dr. Halsey and SPARTAN-087 arrive and are trapped along with the rest of the human survivors. Halsey sends a distress signal piggybacked on Cortana's October 28 signal.
• Having received Halsey's signal, SPARTAN-043, SPARTAN-058, and SPARTAN-104 redeploy from Earth to Onyx aboard a captured Covenant ship. They rendezvous with Halsey. The UNSC survivors are forced to retreat underground as a newly arrived Covenant fleet beings landing troops.
• Battlegroup Stalingrad arrives to retrieve the survivors, but is unsuccessful due to the Covenant presence. Despite superior tactical skill, the UNSC battlegroup is destroyed.
• Halsey and the other survivors hold off pursuing Covenant troops long enough to flee to the safety of the Shield World and seal the entrance.
• Sentinels annihilate the remaining Covenant forces as Onyx 'disintegrates'.
• The Battle of Onyx ends.

Sources

Halo 1 Halo 2 Halo: The Fall of Reach Halo: The Flood Halo: First Strike Halo: Ghosts of Onyx