Editing Halcyon-class light cruiser

|class identification = [[Hull classification symbol]]: '''C'''{{Ref/Book|Id=HCESGuide|Halo: Combat Evolved: Sybex Official Strategies & Secrets|Page=60}}

|class operator      = [[UNSC Navy]]{{Ref/Book|Id=Enc22|Enc22|Page=119}}

|class architect      = [[Robert McLees (ship designer)|Dr. Robert McLees]]{{Ref/Book|Id=Enc11|Enc11|Page=261}}

|width          = {{Convert|1155.73|ft|m|sp=us|sigfig=5|disp=flip}}{{Ref/Reuse|H1GameData}}{{Ref/Generic|Id=data drop|[[Data drops]]|Detail=Data drop 5}}

The '''''Halcyon''-class light cruiser''',{{Ref/Reuse|Enc22}} known as the '''Human Attack Ship class C-II''' by the [[Covenant]],{{Ref/Novel|Id=TF|HTF|Chapter=Prologue}} is a [[United Nations Space Command]] cruiser starship classification designed by [[Robert McLees (ship designer)|Dr. Robert McLees]] before [[2507]], with a [[hull classification symbol]] of '''C'''. Originally designed for attack and defense role in mind,{{Ref/Book|Id=EVG|EVG|Page=42}} they were also capable of being used as troop and supply transports.{{Ref/Reuse|Enc11}}

The most curious element of the ''Halcyon''-class was their unusual frame construction. Designed by [[Robert McLees (ship designer)|Doctor Robert McLees]], they made use of a series of internal cross bracings and [[Titanium-A armor|Titanium-A]]{{Ref/Reuse|FoRC29}} honeycombs. This feature gave the class a reputation for enduring serious punishment, despite their usage of older, heavier armor that provided less protection than modern standards. ''Halcyon''-class cruisers were known to remain operational despite suffering breaches to all compartments and losing 90% of their armor. However, such a scheme was costly and grossly overmassed compared to more conventional measures, which led to it being dropped after the first eleven cruisers.<ref name="FoRC25">'''Halo: The Fall of Reach''', Chapter 25</ref> Aiding in this, corridors aboard the ''Halcyon''-class possessed retractable containment bulkheads which could seal off breached or overrun sections of the ship.<ref name="maw">'''[[Halo: Combat Evolved]]''', campaign level ''[[The Maw]]''</ref> During emergencies, the environmental systems could vent each section to asphyxiate the occupants within.{{Ref/Novel|Id=TFC1|HTF|Chapter=1}} The ship was pocketed with numerous maintenance and service corridors that ran the length of the ship. If necessary, these expansive corridors, including a [[Class Seven service corridor]] running along the dorsal structure of the vessel, could permit passage to [[Warthog]]s and some sections were large enough to accept [[Pelican]]s.{{Ref/Reuse|maw}}

By far the most expansive and famous of these were the alterations the UNSC ''Pillar of Autumn'' received as part of preparations for Operation: RED FLAG. Selected due to its possession of the honeycomb framing scheme, the refit took advantage of the need to replace its hull plating with reformulated [[Titanium-A armor]], which reduced its mass but also freed up internal volume. Much of this would be taken up by hangars and [[SOEIV]] launch bays, although the former required the removal of long-term accommodations.{{Ref/Reuse|Enc22}} Power was improved with an experimental reactor setup that could not only increase output by up to 300% for short periods of time, but made use of a very efficient laser-induced ion cooling system. Armament was finally expanded, with a MAC capable of firing three times on the same charge,{{Ref/Novel|Id=FoRC29|FoR|Chapter=29}} 32 M58 Archer missile pods, 8 Mark 33 Spitfire naval coilgun batteries, and six M66 Sentry autocannons. 18 M910 Rampart point defense guns with overlapping fields of fire provided the final layer of protection against missiles and incoming munitions.{{Ref/Book|Id=WFPoA|HWF|Page=24-25}}

When the [[Human-Covenant War]] erupted in [[2525]] a number of ''Halcyon'' cruisers were reactivated from storage and refitted. Some participated in remarkably early engagements of the war; [[Preston Cole|Vice Admiral Cole's]] [[Battle Group X-Ray]] fought the [[Battle of Harvest]] with a number of these cruisers.{{Ref/Comic|HWG|Id=HWG}} Even this early on, it was evident that the ''Halcyon''s were not invulnerable; {{UNSCShip|Constantinople}} was lost with all hands during this battle. Meanwhile, the UNSC ''Pillar of Autumn'' took heavy damage when it teamed up with three other ships to destroy [[CCS-U321|a]] {{Pattern|Ket|battlecruiser}} during the [[Battle for Arcadia]].{{Ref/Level|HW|Arcadia City}} This led to a substandard performance record for the cruisers, and they'd come to be known as a joke within the [[UNSC Navy]].{{Ref/Reuse|FoRC25}}

''Halcyon''-class cruisers continued to serve throughout the conflict. As the losses continued to mount, the UNSC were forced to consider radical improvements to keep the ships competitive. The UNSC ''Pillar of Autumn'' received one such overhaul as part of the planned [[Operation: RED FLAG]], and used it to great effect during the subsequent [[Fall of Reach]], where it was instrumental to the destruction of a {{Pattern|Kewu|battleship}}.{{Ref/Novel|TFOR|Id=FoRC36|Chapter=36}} Later, during the approach to [[Alpha Halo]], it managed to destroy four Covenant [[capital ship]]s before being forced to crash onto the ring's surface, a phenomenal performance for a UNSC cruiser.{{Ref/Level|CE|Pillar of Autumn (Combat Evolved Level)|Pillar of Autumn}} Ultimately, the ''Autumn'' met its end when its engines were overloaded to destroy the Halo and much of the Covenant's [[Fleet of Particular Justice]],{{Ref/Level|CE|The Maw}} leaving behind only a handful of survivors.

The first of the {{Class|Autumn|heavy cruiser|heavy cruisers}}, commissioned into service following the end of the Human-Covenant War,<ref>'''[[Halo 4: The Essential Visual Guide]]'''</ref> would be built from the recycled hulls of surviving ''Halcyon''-class vessels.{{Ref/Book|Id=WFA|HWF|Chapter=Human, Cruisers}}