Pillar of Autumn

The Pillar of Autumn is a heavily modified United Nations Space Command Halcyon-class cruiser in the Halo: Combat Evolved Xbox video game. It is also mentioned in the official Halo prequel book, "The Fall of Reach".

Structure
Prior to the war with the Covenant, the Pillar of Autumn was due to be decommissioned. Instead, in 2550 it was refitted to serve in active duty.

When first conceived in 2509 the UNSC forces considered the ship a joke. It was exorbitantly expensive, suffered from poor maneuverability in combat situations and was woefully lacking in firepower. In its favor, the ship's superstructure was honeycombed with Titanium-A, giving it superior structural integrity and making it resilient to any attack. The superstructure was laced with struts, bulkheads and pressure doors, making it nearly impossible to destroy completely, as sections could be isolated independently from each other. Reports had Halcyon-class cruisers operating with breaches on all decks and 90% of the ship's armor destroyed.

As part of its 2550 refit, the ship's Archer missile pods and Magnetic Acceleration Cannon were upgraded to serve in the Human-Covenant war. After its refit, the Pillar of Autumn was much more formidable in combat. Modifications to the ship included increased Archer missile capacity, a greatly improved power plant with unique cooling methods and an upgraded Magnetic Accelerator Cannon capable of firing three rounds on a single charge. Overall, the ship's armaments consist of an advanced Magnetic Acceleration Cannon, 128 Archer missile pods, 40 50mm cannons, 1 Shiva nuclear missile that could be sent out in a remote Longsword fighter, and 3 Havok nukes. These modifications occur in the book Halo: The Fall of Reach. The ship is also featured in the novel tie-in Halo: The Flood.

The Pillar of Autumn's engines were replaced with a prototype design. Instead of more traditional cooling systems, "a laser-induced optical slurry of ions chilled to near absolute zero" cools the engine cores. The lasers draw power from the reactors, resulting in a system more efficient than previous coolant driven systems. Two smaller, secondary reactors "come online to supercharge the main reactor." This enables the new engines to run at 300% for an unstated amount of time, which is a unique capability that no other UNSC ship possesses.

Halo
The Pillar of Autumn was one of only a few ships to escape the Covenant armada following the fall of the planet Reach. The ship made a 'blind' jump through Slipspace (though it was actually a calculated guess by the AI Cortana, who interpreted a sequence of characters gained from a Forerunner artifact) to the gas-giant Threshold, location of Halo Installation 04. The Covenant believed the ring world was their religious icon "Halo", capable of carrying out their "Great Journey".

Covenant battleships, already at the ring due to their much faster Slipspace engines, intercepted the Pillar of Autumn upon its arrival at the planet Threshold. Reluctant to use their more powerful weapons for fear of causing collateral damage to "Halo", the Covenant armada attacked with relatively light fire in coordination with numerous boarding craft filled with assault troops. The boarding parties were charged with retrieving senior officers, including the commanding officer Captain Jacob Keyes, for interrogation. They failed in this attempt. Outmatched on their own ship, Captain Keyes later had the Autumn's crew and marines escape using the remaining lifeboats.

Keyes and the rest of the command staff managed to crash the ship on the surface of Halo while the many surviving Marines quickly formed a formidable resistance movement. But their only chance of holding out was to search and salvage the grounded Autumn for additional weapons, vehicles and equipment for their base, before the Covenant could claim the entire ship. After 343 Guilty Spark's true intentions of activating Halo were revealed, Cortana and the Master Chief manually overloaded and then detonated the ship's fusion reactors, setting off an enormous explosion that destroyed Halo, thus preventing the escape of Flood and Covenant forces, as well as preventing the galactic devastation that would have resulted from the ring's activation.

The Pillar of Autumn's sister ship was the Dawn Under Heaven.

Issues Over the Size of the Pillar of Autumn
During the game, the apparent size of the Autumn changes. In the opening shots, the camera pans in towards the ship's bridge, which takes the form of an underslung cupola. The scale of this feature is obvious from the human figures within. It is possible to extrapolate the overall size of the vessel from this feature (Around 1.17km). In the final stages of the game, Master Chief attempts to reach a Longsword fighter to make his escape. In doing so, he drives a Warthog across the spine of the ship. The Autumn appears as much as three times larger in this incarnation. However, this keeps with the science fiction tradition of the inside of vessels being larger than the outside, like the Millennium Falcon. It can be deemed that the size of the Pillar of Autumn appears diminished due to its high speeds, hence due to Einstein's relativity theories, its length has been dialated.