The UNSC Pillar of Autumn was a Halcyon-class Cruiser. Informally, she was simply
referred to as "The Autumn", and informally abbreviated as the "PoA".
Early on in the Human-Covenant War, it participated in the Battle of Arcadia in February 2531. The
Autumn along with three other ships managed to fire on a Covenant ship that was still recharging it's shields, most likely
destroying it. Though heavily damaged, it delivered experimental Rhinos to the surface to penetrate Covenant shield defenses.
Mothballed and due to be scrapped like the remainder of the Halcyon-class cruisers (said to
be the toughest of all cruisers despite their poor speed and firepower), the Autumn was brought back into active duty
during the Human-Covenant War. She had undergone a refit in 2550 to serve, interestingly enough, in the Zeta Doradus System.
Under the command of Captain Jacob Keyes, she was to serve as an inconspicuous launch pad, for a covert offensive involving locating the Covenant
homeworld and capture of Covenant leadership, the Prophets by SPARTAN-II Super soldiers and received a refit to prepare her
for the upcoming mission. The refit rectified a number of deficiencies in the original design and made her a competitive re-addition
to the sorely pressed UNSC Navy. At the time of her destruction in 2552 she was 43 years old. The Pillar of Autumn
was ultimately unable to embark on the aforementioned operation due to the UNSC defeat at the Battle of Reach and was one
of the few ships to escape the disaster, albeit with moderate damage and the loss of a third of its tech staff. Although the
Cole Protocol demanded a random Slipstream jump, the AI Cortana, without the knowledge of the crew, purposely guided the ship
to the planet Threshold based on map coordinates extracted from a Forerunner artifact on Sigma Octanus IV. The result was
the discovery of Installation 04, or "Halo".
However, a large fleet of Covenant cruisers were located on the other side of
the planet. They had followed the PoA through slipspace from Reach. A brief and uneven battle against a Covenant battle group
of a dozen superior CCS-class Battlecruisers then occurred in near-Threshold space. The orbital battle resulted in
critical damage being inflicted upon the Pillar of Autumn. Enemy boarding parties disabled the MAC's fire control with
a demolition charge, but not before she made a good account of herself by destroying four enemy warships and damaging several
others. The Pillar of Autumn's survival against superior forces was due in part to a Prophet's directive to disable,
rather than destroy her, out of fear that her destruction might damage Halo, which had religious significance to the Covenant.
Before setting an "emergency-landing," the Autumn released its cryo tubes into space, one of them containing SPARTAN-058,
Linda. The ship was then crash landed onto Halo by one of Cortana's subroutines. The vessel, damaged beyond repair, tore a
deep gash in the ground for several hundred meters, bounced, then came to rest upright and balanced over a cliff on a barren
Prior to the crash, much of her crew had taken to the escape pods, including Cortana who was being
carried within the Master Chief's suit. Others were evacuated by Pelican dropship or even in drop pods, as was the case for
a complement of ODSTs. Despite the confusion most of the crew survived, to reach Halo and engage Covenant ground forces.
Later, the surviving Pelicans were employed to retrieve munitions from the crashed ship to sustain
this effort. The human forces successfully neutralized the Covenant vehicles and some of the infantry stationed at the crash
site and retrieved weaponry and vehicles to use in their guerrilla war against the Covenant.
Despite the abuse sustained during the space battle and the following crash the Pillar of Autumn
remained intact, and was subsequently occupied by investigating Covenant forces and later by Flood. The threat posed by the
latter was deemed sufficiently great for ODST Major Silva to give SPARTAN-117 and Cortana the order to detonate the ship's
still-functioning fusion power cores in a bid to destroy Halo, thus preventing the Flood from escaping.
Having manually triggered the destabilization of the power cores after subsequently destroying the
casings on the cores, an intervention by the AI 343 Guilty Spark halted the remote detonation, SPARTAN-117 and Cortana commandeered
a Longsword from one of the Pillar of Autumn's docking bays and achieved a safe minimum distance before the ship exploded,
causing the ring-world to fall apart. According to Doctor Halsey its memory would live on for years to come.