Battle over Installation 04

On September 19, 2552, the  entered the Soell system. What followed was a battle over Installation 04, as forces of the Fleet of Particular Justice attempted to stop the human forces of the cruiser from landing on Installation 04.

Prelude
On August 30, the Pillar of Autumn fled the Fall of Reach, along with its complement of personnel. The ship was followed by the Fleet of Particular Justice, led by the Fleetmaster Thel 'Vadamee, who hereby ordered all vessels of the fleet to contribute two fightercraft to advance recon pickets to ensure the human cruiser would not be able to slip past the fleet defenses, while the fleet held position on the far side of the ring. The fleet had arrived earlier than the Autumn thanks to their superior slipspace drive technology. The Minor Prophet would declare the matter one of religious significance and invoke his right to leadership, though this would be contested on the grounds of 'Vadamee, who insisted he would not relinquish command to a politician in combat. The two would convene aboard the fleet's flagship Seeker of Truth to contact High Charity for guidance, though no contact was able to be made, and no decision reached.

Upon arriving in the Soell system, the Pillar of Autumn deployed GA-TL1 Longsword fighters for sentry screening. The Prophet would order the Covenant fleet to hold fire on the cruiser for fear of damaging the ring, though 'Vadamee would later ignore this order anyway. The prophet would order the deployment of boarding craft and an Ossoona, alongside ordering the battlecruisers Purity of Spirit and Undiminished Entelechy to perform secret close-range surveys of the installation.

The battle
The first shot fired in the battle was suffered by the Pillar of Autumn only twenty minutes after its arrival when a Seraph managed to slip through the cruiser's sentry screening. The fighter was shortly destroyed by one of the escort Longswords, though another wave of fighters would be inbound, with the boarding craft behind. As the cruiser cleared the gas giant Threshold, the crew were met with the sight of a gargantuan megastructure of neither human nor Covenant origin. Cortana was able to identify four battle groups of three s, estimating she'd be able to use the cruiser to get 3-4 kills on the Covenant fleet with those odds. At this time, technicians Samuel Marcus and Thom Shephard were authorised to wake up Spartan John-117 from stasis.

The cruiser would continue to be assaulted by several Morsam-pattern Seraphs and Type-27 Banshees throughout the battle, who would be fended off by the ship's M910 Rampart point defense network. Later on, the ship would take fire from Covenant pulse laser turrets.

Unbeknownst to either side, the Forerunner installation was not inert. Monitor 343 Guilty Spark attempted to contact the Pillar of Autumn and warn of them of the ring's danger, insisting the cruiser retreat to a safe distance of one light-year. The monitor prepared several s to fire on the vessel and gave it thirty seconds to change course, though he stopped once he realised the ship belonged to Reclaimers and cleared the ship for landing. The monitor disabled the ring's defensive systems, but warned the crew not to disembark once they landed.

Boarding actions
Out of fear of damaging the ring, Covenant forces were ordered by the Minor Prophet of Stewardship to concentrate on boarding actions as opposed to firing ship-borne weaponry. The Covenant launched waves of boarding craft to drop off troops on the ship. Aboard the Pillar of Autumn, the ODST complement under command of Major Antonio Silva was ordered to defend the ship's engine rooms and power plant, while 5th Platoon was ordered to secure airlocks on deck 11 and 14th Platoon was ordered to rendezvous with the 22nd Tactical at bulkhead charlie-14. In the hangar bay, Sergeant Avery Johnson gave a speech to his Marines. To assist in the ongoing defensive operations, one bridge crew member operated the life support controls and used them to suck out their air from compartments occupied by Covenant forces.

Following his brief wakeup, John-117 was ordered to report to the bridge. Along the way, he would pass several firefights going on as boarders began to engage UNSC Marine fireteams, before eventually arriving at the bridge. Another blast, caused by an antimatter charge, rocked the ship and brought the ship's primary MAC gun offline. Consequently, the Spartan was informed that Keyes was enacting the Cole Protocol; the crew were to be evacuated and Cortana taken by John to ensure she did not fall into Covenant hands. Keyes would fly the ship in manually before evacuating himself. The Spartan left the bridge and proceeded to try and find a lifeboat, fighting through many corridors filled with Covenant. Eventually, the ship began rocking with the impacts of plasma torpedoes and lifeboats began launching. At the same time, the Covenant boarding craft began to latch onto the now-vacant airlocks to insert troops the same way the UNSC left the ship.

Two of the Unggoy personnel assigned to board the ship, Yayap and Gagaw, were passing a pile of Covenant corpses when they noticed some slight movement - a special operations Elite, clad in black armor. While Gagaw wanted to abandon the Elite as he would do for the grunts, Yayap instead suggested the grunts evacuate the elite, thereby ensuring the small unit would be unable to engage combat for the rest of the boarding action.

In the ODST drop bay, Major Silva assigned Fireteam Raven to defend the Pillar of Autumn. The fireteam proceeded to exit the drop bay and tour several corridors before being contacted by Wellsley; several of the ship's M910 Rampart guns had been taken offline, and the team would need to perform a spacewalk to man them and fend off waves of fighters. The team were able to shoot down multiple waves of Seraph and Banshee before beginning to head back into the ship. Meanwhile, the ODST complement under Lieutenant McKay had performed their jobs successfully, and had taken to stacking Covenant bodies like firewood to maintain clear fields of fire in the reactor bay. Unfortunately for the ODSTs, the human side had also taken many casualties.

Amidst the boarding action, Special Operations Sangheili Isna 'Nosolee was selected by the Minor Prophet of Stewardship to infiltrate the vessel as an "Ossoona", or "Eye of the Prophet". 'Nosolee had three goals; capture the shipboard AI, capture command personnel and record anything he saw. Armed with six plasma grenades and a plasma pistol, the Sangheili engaged active camoflage and exited his boarding craft.

Evacuation
"Captain Keyes is tired of our company and wants us to leave this tub. There’s a construct down there, complete with an atmosphere, gravity, and the one thing Marines love like beer—and that’s dirt beneath our feet. Most of the crew—not to mention your fellow jarheads—will be leaving the ship in lifeboats. They’ll ride to the surface in air-conditioned comfort, sipping wine, and nibbling on appetizers. Not you, however. Oh no, you’re going to leave the Pillar of Autumn by a different method."

- Silva, addressing his troops.

With Keyes planning to crash the Pillar of Autumn on the surface of the ringworld, a general evacuation was ordered. For most personnel, this meant evacuating the ship in SKT-9 Bumblebee lifeboats. Eventually, the Master Chief was able to find a lifeboat that had not yet launched, and paused to throw a stumbling marine into the craft before boarding himself. Fireteam Raven were just behind and covering fire, and soon headed for the SOEIV drop bays to join their comrades in dropping "feet first into hell". The troops were ordered by Silva to abandon the reactor bay and make preparations to drop, with McKay entering her pod last and launching just as someone began to play the Helljumpers' anthem over the radio network shared by all the drop pods. Despite being against regulations, nobody ordered the music to be turned off.

Despite the rest of the UNSC personnel abandoning in lifeboats and drop pods, several naval pilots and ground crew including Carol Rawley devised an alternate plan; to attempt to take off from the ship in their D77-TC Pelican dropships - figuring that even dying behind the stick of her craft was better than by a Covenant weapon. The pilot team managed to make their way to the Pelican bays, thankful to find their craft undamaged and fully fueled. As they ran an abbreviated pre-flight checklist, they spotted a Covenant boarding craft lining up to enter the bay, though the Pelican's chin-mounted 70mm chaingun took care of the dropship without issue. By this time, the Autumn was beginning to scrape the atmosphere of the Halo, meaning the ships would have to be extremely lucky to deploy due to the wall of fire building around the ship. Nonetheless, the Pelicans were able to deploy without issue.

As the crew finished evacuation, the Covenant attempted to launch a last assault on the command deck. The attack was repelled, and fifteen minutes later, reports began to come in that the Covenant were beginning to evacuate themselves. This left the area around the bridge clear of hostiles, and Keyes free to use Cortana's subroutines left in the system to bring the ship in before evacuating himself. Out of the corner of his eye, Keyes noticed a shimmering but brushed it off as tiredness. However, what he had in fact seen was the shimmering of 'Nosolee's camoflage system, who remained thankful he hadn't been spotted. The Sangheili realised the ship's AI had been removed or destroyed, and voted to try to capture the captain. Eventually, the bridge crew began to depart their stations as their work finished, and the Ossoona fell into step behind them. The bridge crew's lifeboat was nearby and six marines had been assigned to guard it, though three were dead. 'Nosolee entered the lifeboat, careful not to brush any of the humans as he found space at the front to stand unnoticed, though this plan ultimately failed as Keyes took the sidearm of one of the marines and fired at the Sangheili. The Sangheili suddenly appeared as the camo generator failed, and floated in the mcirogravity.

Aftermath
The Pillar of Autumn would land on the surface of Installation 04, coming to rest on a large clifftop. The UNSC forces evacuated from the ship would land in scattered groups across the surface of the ring, with the ODSTs under Major Silva quickly coming together and organising to capture a mesa later referred to as Alpha Base\. This base would prove crucial to the UNSC campaign on the ring in the coming days, providing a place to reorganise and resupply. Covenant forces would later occupy the crash site, though a raid conducted the next day would see supplies and vehicles moved to Alpha Base. Fireteam Raven would land on the ring in time to see the Autumn's impact, and ultimately begin a 28-hour long trek to link up with McKay's forces during the raid.

Following his landing on the ring, Keyes and the rest of the bridge crew would later be captured by the Covenant. Meanwhile, John-117 would proceed to begin rounding up survivors for evacuation by Rawley's Pelican.

By 2558, simulations of the Undiminished Entelechy and the Fleet of Particular Justice in the battle were depicted in UNSC War Games simulations. In the simulations, the fleet's s were replaced by post-war Hekar Taa-pattern Blockade Runner.

List of appearances

 * Halo: Combat Evolved
 * Halo: The Flood
 * Adjunct
 * Halo: Reach
 * Halo: Combat Evolved Anniversary
 * Terminals
 * Halo 2: Anniversary
 * Terminals
 * Halo 5: Guardians
 * Halo: Fireteam Raven