Battle of Installation 00

The Battle of the Ark was a large engagement between the UNSC-Covenant Separatist Alliance, the Covenant Loyalists, and the Flood. It was the final battle of the Second Flood outbreak, the Human-Covenant War, and the Covenant Civil War.

The Prophet of Truth, having successfully activated the artifact in New Mombasa, left Earth through a Slipspace portal to the Ark, a Forerunner structure that can be used to fire all of the Halo installations at once. Despite Lord Hood's urging, Commander Keyes took the UNSC frigate UNSC Forward Unto Dawn with a small fleet of Separatist ships lead by the carrier Shadow of Intent and proceeded through the Slipspace portal and arrived at the Ark. The Separatists immediately engaged the Brute fleet stationed to protect the Prophet while the Dawn deployed shock troopers to locate Truth. 343 Guilty Spark, now working with the UNSC-Separatist Alliance, led SPARTAN-117 and the Arbiter to the Ark's Cartographer where they pinpoint the Prophet's location. By then Truth had already holed himself in a secure facility in the core of the Ark and had activated a large barrier around the entire core to ward off the attacking forces.

The UNSC ground forces, along with Separatist reinforcements, assaulted three emitter pylons that powered a small section of the barrier. When the defending forces were eliminated and the pylons shut down, the Shadow of Intent began its attack on Truth. At the same time the former Covenant city ship High Charity arrived from Slipspace and crashed on the Ark. Debris spread from the city ship heavily damaged the Shadow of Intent and helped spread a new Flood infestation on the Ark. Without any heavy support, SPARTAN-117 and the Arbiter personally attacked the facility where Truth was to activate the Halo installations.

Sergeant Major Johnson, who had disappeared during the assault, was in fact captured by Truth's forces and was being tortured into pressing the final switch to activate the other Halos. With SPARTAN-117 and the Arbiter to far away to stop Truth, Commander Keyes grabbed a Pelican dropship and crashed into the facility to rescue Johnson, but was killed soon after. The Gravemind dispatched Flood forces to assist SPARTAN-117 and the Arbiter in preventing the Halos' activation and the Arbiter killed Truth in the process. However, the Gravemind betrayed them and while Johnson managed to escape with Commander Keyes' body in the Pelican, SPARTAN-117 and the Arbiter had to fight their way outside.

343 Guilty Spark had managed to facilitate the making of a new Halo through the Ark, explaining that a tactical pulse from it would eliminate the Flood infestation. However, this new Halo lacked an Activation Index. The only way they could get another Index was to rescue Cortana from High Charity since she still possessed the Index from Installation 04. Through a tough battle, SPARTAN-117 and the Arbiter successfully entered the ruins of High Charity and recovered Cortana, using a partly-damaged Pelican to escape.

With the Index secure, the Arbiter ordered that the remaining UNSC forces relocate to the Separatist ships and escape back through the Slipspace portal to Earth while he, SPARTAN-117 and Sergeant Major Johnson moved in on the Control Room of the incomplete Halo. The UNSC Forward Unto Dawn was left behind for them to use to escape. By now the Gravemind had relocated to the new Halo. The three heroes with 343 Guilty Spark made it through waves of Flood to the Control Room. 343 Guilty Spark explained that the new Halo would be ready to fire within days, but with Flood moving in all around them Johnson disagreed and went to activate it.

343 then went rampant, killing Johnson and attacking SPARTAN-117 and the Arbiter. But SPARTAN-117 managed to destroy 343 and start the firing sequence for the new Halo. He and the Arbiter then took Johnson's Warthog and rushed towards the Dawn as the incomplete Halo powered up and started breaking apart. The two drove their way through hordes of Flood and Sentinel drones and made it to the Dawn where the Arbiter took the helm and steered the Dawn into Slipspace just as the new Halo fired. However, the Slipspace portal collapsed as the Dawn entered it and while the forward half with the Arbiter made it to Earth the rear half fell out out Slipspace with Cortana and SPARTAN-117 and disappeared.

With Truth dead, the Halos deactivated, and the Flood destroyed, the Battle of the Ark ended the Human-Covenant War. A monument was erected in New Mombasa in remembrance of those who gave their lives in the war including SPARTAN-117 who is labeled MIA. The Arbiter and his surviving brethren depart Earth for their homeworld.