UNSC Pillar of Autumn

''Pillar of Autumn redirects here. For the Halo: Combat Evolved level, see The Pillar of Autumn (level).''

"There was only one ship."

- Thel 'Vadamee

"One? Are you sure?"

- Prophet of Regret

"Yes. They called it the Pillar of Autumn."

- Thel 'Vadamee

The UNSC Pillar of Autumn, (Hull Classification Symbol C-709), was a  in the UNSC Navy. Informally, it was simply referred to as the Autumn or abbreviated as the "PoA". The Autumn was retrofitted with advanced weaponry and technology in preparation for a special operation to seize a Covenant warship and subsequently capture the Covenant leadership. Prior to the launch of this mission, the Covenant fleet attacked Reach, during which the Autumn was a major participant.

Following the Fall of Reach, the Pillar of Autumn jumped to the Threshold system, where she encountered a pursuing Covenant fleet and Installation 04. Her captain, Jacob Keyes, landed the ship on the Halo installation, where her surviving complement mounted a resistance against the Covenant and later the Flood. Following the release of the Flood, the Master Chief detonated the Autumn's fusion reactors in order to destroy Installation 04.

Early years
The ship was constructed over Mars in 2509. Early on in the Human-Covenant War, the Pillar of Autumn participated in the First Battle of Arcadia in February 2531. She, along with three other ships, managed to engage on a Covenant ship that was still recharging its shields. Though she was heavily damaged, the Autumn delivered experimental Rhino units to Arcadia to penetrate Covenant shield defenses on the colony world's surface.

Refit
Mothballed and due to be scrapped like the remainder of the Halcyon-class cruisers, the Autumn was again brought in to active duty. She had undergone a refit in 2550 to serve in the Zeta Doradus System. She was then relocated to the UNSC stronghold Reach in preparation for her role as a launch pad for a covert operation under the command of Captain Jacob Keyes. The initial plan of the mission was to have the Autumn, retrofitted with state-of-the-art technology, disable a Covenant warship intact. SPARTAN-IIs assigned to the Autumn would then board the ship, locate the Covenant homeworld, and capture the Covenant leadership to force a truce. The UNSC AI, Cortana, chose the Autumn for the mission for its skeletal structure, known for being able to operate under intense structural failures, which was designed by Dr. Robert McLees.

Fall of Reach
Before the Autumn could embark on this operation, a Covenant armada attacked and subsequently destroyed Reach. The SPARTANs aboard the Autumn were either sent to Reach's surface or accompanied John-117 to destroy the navigation data of a ship that failed to enact the Cole Protocol; the former were presumed KIA when the Covenant glassed the planet while only 117 survived the latter. Meanwhile, the Autumn managed to severely damage several enemy ships over Reach before enacting the Cole Protocol, attempting to lead the Covenant fleet away from Earth. Instead of using a random vector, the AI Cortana guided the ship to the Threshold system based on coordinates obtained from a Forerunner artifact on Sigma Octanus IV. The result was the human discovery of a Halo ringworld, Installation 04.

The Battle of Installation 04
Upon arrival in-system, the Autumn encountered a large battle group of Covenant s that had followed her vector from Reach. The Covenant High Command, reluctant to use plasma torpedoes near Halo, instead send boarding parties to disable the warship. The Autumn destroyed four enemy vessels over Installation 04 before Covenant soldiers disarmed her MAC, rendering the ship defenseless. Keyes then gave the order to abandon ship, sending John-117, the only active SPARTAN left aboard, on a lifeboat to Halo's surface with Cortana to prevent her capture. The Autumn then jettisoned its cryo pods before Keyes crash-landed the ship on the ringworld's surface.

Many of the Autumn's crew had evacuated the ship through life boats, Pelican drop ships, or ODST drop pods. One group of survivors established Alpha Base on Installation 04, using Pelicans to transport materiel from the relatively intact warship to sustain the humans' guerrilla war against the Covenant.

After the release of the Flood and the Monitor 343 Guilty Spark's subsequent attempt to activate Halo, Cortana reasoned that she and SPARTAN-117 needed to destroy the installation, determining that detonating the Autumn's fusion reactors would be the best way to do so. Cortana's attempt to set off the reactor core from the bridge failed when 343 Guilty Spark stopped the self-destruct sequence from the Engineering section. The Master Chief used explosives to destroy the engine shields and force a chain reaction. After Echo 419 was downed after an aborted extraction of SPARTAN-117 from the Autumn, Cortana and the Master Chief made their way to a docked Longsword fighter and used it to escape Halo's destruction.

Specifications
The Pillar of Autumn was roughly 43 years old at the time of her escape from Reach and later destruction on Installation 04. She was a cruiser of the Halcyon-class, the smallest cruisers in the UNSC Fleet. Like other Halycon ships, the Autumn was equipped with a honeycombed internal bracing structure that allowed it to function even after sustaining critical levels of damage.

Power Plant
The Pillar of Autumn was refitted with an improved nuclear fusion engine that featured two smaller reactors around a larger one, which were capable of boosting the overall power output by 300% for a short time if needed.

Fusion reactors generate extreme heat which must be removed in order for them to remain active without overheating. The Autumn's overhauled reactors were an especially severe case of this. Usually, the excess heat was conducted to a chemical agent which would then vent into space. However, the Autumn's upgraded specifications also included an upgraded cooling system, which featured a "laser-induced optical slurry of ions chilled to near-absolute zero", which is far more efficient than the typical method and removed the reliance on expendable chemical temperature-control substances. In essence, the amount of excess heat removed by the new system increased as the reactors' output did. This self-regulating and self-cooling power plant was critical in combat since it virtually eliminated a commander's concerns about overheating and slagging a ship's engines.

The Pillar of Autumn's reactor was able to be overloaded by explosives, either grenades or rockets, destroying the vulnerable vent cores. Once these were destroyed, the reactor began to go critical, resulting in temperatures of over 100,000,000 degrees and a thermonuclear explosion that tore apart a Halo Installation.

Armament
The upgraded Pillar of Autumn received extensive refits, including several to its weapons systems. Eventually, it was host to a very powerful armament; far in excess of the original Halcyon-class ships.
 * With extra power capacitors and power recycling systems, the Pillar of Autumn could fire three consecutive shots per charge.
 * The MAC gun fired lighter projectiles compared to most ship grade MACs, but these rounds worked much like Shredder Rounds. Each charge was able to fire 3 rounds.
 * 300 Archer Missile Pods which were arranged in thirty columns and ten rows. Each pod contained 26 individual devices, equaling 7800 missiles
 * Four Shiva-class Nuclear Missile, one loaded onto a remote-controlled Longsword interceptor, and three ship-launched.
 * Forty 50mm MLA Auto-cannons with overlapping fields of fire for point defense against single ships. These cannons were later salvaged by the surviving humans on Installation 04 for Alpha Base.

Engine Room
The Pillar of Autumn 's engine room was a large, three-deck high chamber allowing access to the fusion engine core. Side passages allowed for movement from the bottom deck all the way up to the catwalks on the third. The manifolds into the cores were suspended above the second deck. Controls on the third retracted these manifolds, exposing a vent that led directly into the core. It was using this method to expose the core via the vents that the Master Chief ultimately destroyed the ship and Installation 04. This room is the largest room in the Pillar of Autumn with the exception of the hangar bay and the "Leap of Faith" room.

Airlocks

 * Airlock 31, 32: Lifeboats destroyed by the Covenant to make way for a Boarding Craft.
 * Airlock 51: Lifeboat was destroyed by unseen Covenant artillery as it departed from the airlock.
 * Airlock 52, 53, 61, 62, 63: Lifeboats managed to make it out of the vessel.1

1 Airlock 61: the Master Chief, Cortana, nine other Marines on board and the Bumblebee pilot.

Trivia

 * In cut scenes, the Pillar of Autumn never moves, it is just a piece of BSP geometry. However, the cameras and the background moved in such a way that it gave the illusion of movement.
 * The Pillar of Autumn is approximately 1.17 km long, a reference to John-117. This, however, contradicts the final level of Halo: Combat Evolved where the player must drive along a 3 km long service corridor that supposedly runs the length of the ship. This was probably for generating the tension and atmosphere necessary for the level.
 * The Marathon logo is prominently displayed on the Pillar of Autumn 's starboard and port sides. The ship's official emblem has the Marathon logo as well. The marathon logo was also visible in the window of the ship in the opening cut scene of the level The Maw.
 * The bulletin board just outside the bridge of the ship contains a number of amusing clips, some throwbacks to Marathon. These can be examined on the first level of Halo: Combat Evolved. The board has a flier for a missing cat called Jonesy. This is a reference to the Alien movies, where the cat's name was Jonesy. The board also has a flier telling Marines to 'Keep it Clean', a quote later used in Halo 3: ODST.
 * Prior to being refit for the Spartan mission, the Pillar of Autumn was equipped with Mark II fusion engines (which supplied only 10% the power of modern reactors), and had just one regular MAC gun and six Archer missile pods.
 * The Pillar of Autumn mess-hall offered a choice between turkey, hamburgers, cheeseburgers, hot dogs, meatloaf, and a dish named Chef's Special. Beverages included cola, water, lemon/lime, lemonade, root beer, coffee, orange juice, hot tea, hot chocolate, iced tea, and Chef's Surprise. These are served in what appear to be vending machines, and are visible in the opening level in Halo: Combat Evolved.
 * The Pillar of Autumn has a sister ship known as the Dawn Under Heaven.
 * In Halo: The Fall of Reach, the Autumn is described as having a command chair. In Halo: Combat Evolved, this chair is absent. Also in Halo: The Fall of Reach, the Autumn seems to have a rotating section in it to simulate gravity. However, in Halo Combat Evolved, the ship has gravity in areas that could not be in a rotating drum. The bridge is an example. As Halo: Contact Harvest pointed out that Human-engineered artificial gravity was in existence in 2525, it is possible that the Autumn was being converted to use artificial gravity. The player may simply not visit areas still using rotating sections.