Unlike its sisters in Aszod, the Autumn was merely placed in long-term storage as military surplus, just in case it should be needed later. The cruiser was later decommissioned with the other Halcyon-class cruisers. The cruiser contributed experimental M-145D Rhino to the ground fighting. The cruiser was heavily damaged engaging two CCS-class battlecruisers.

It saw action during the First Battle of Arcadia against the Covenant in February 2531. Due to its expensive honeycomb structure, the blueprints of the Halcyon-class were radically altered soon after the Autumn 's construction with only the first eleven of fifty possessing it. The ship was launched on December 1, 2510. It was constructed at the Reyes-McLees Shipyards on Mars in 2509 as one of the then-new Halcyon-class cruisers. The Pillar of Autumn was originally designed by Dr. It also inspired the creation of its successor, the Autumn-class heavy cruiser. The Pillar of Autumn had a few sister ships, including the UNSC Dawn Under Heaven and the UNSC Toulouse. The ship's sole remaining combat effective SPARTAN-II, John-117, was forced to detonate Pillar of Autumn 's fusion reactor, destroying the ship and the installation to prevent the installation from firing. Keyes crash-landed the ship on the installation where the surviving crew continued the battle against the Covenant and later, the Flood. There it was engaged by a Covenant fleet guarding Installation 04. The cruiser was guided to the Soell system by the AI Cortana.

The operation was forestalled by the Covenant assault on Reach and the cruiser was one of the few UNSC survivors and fled the system having lost most of its intended SPARTAN-II passengers. Captain Jacob Keyes was placed in command. Prior to the Fall of Reach, Pillar of Autumn was selected to support Operation: RED FLAG, a SPARTAN-II operation to capture Covenant leaders. It was informally referred to as the Autumn, and its name abbreviated to 'PoA.' The motto for the ship was Ad Arcendam Hostium UNSC Pillar of Autumn ( HCS: C-709) was a Halcyon-class light cruiser in the UNSC Navy. Thel 'Vadamee explaining the Battle of Installation 04 to the High Council.

Halo 1 hidden room pillar of autumn