Battle for the Truth and Reconciliation

Numerous raids took place over Installation 05 as the Marines of the boarded the damaged CCS-class Battlecruiser, the Truth and Reconciliation.

First Raid - Rescue the Captain
Shortly after the evacuation from the Pillar of Autumn, Captain Jacob Keyes was captured by Covenant forces and taken to the Truth and Reconciliation, where is was promptly imprisoned in one of its detention centres.

After word got out of his capture when AI Cortana hacked into the Covenant BattleNet, a force of Orbital Drop Shock Troopers dressed in urban-warfare fatigue assisted Master Chief Petty Officer John-117; a SPARTAN-II, in the initial boarding of the ship via the gravity lift which was based below it. Entering the ship, the group was attacked by numerous waves of the ship's military complement.

Leaving the ODSTs in the ship's control centre, the master chief proceeded to hunt for Captain Keyes solo. Eventually finding him and several imprisoned marines, the group headed back to the control room. However, in the time it took John to find Keyes and head back, the ODSTs guarding the rally point had been slaughtered by Energy Sword-wielding zealots.

After Covenant banshees located the Pelican Echo 419, which was giving support for the mission, Keyes changed the objective. Rather than waiting for Echo 419 to return safely, the group went to one of the Truth and Reconciliation's hanger bays, where they stole a Type-25 Troop Carrier.

Second Raid - Return to the Captain
During the Battle of the Flood Containment Facility, Captain Keyes was infected by the flood super cell via an Infection Form. Initially becoming a Combat form, his tactical knowledge was considered important to the parasitic organisms, and he was converted into a Proto-Gravemind along with a Sangheili officer after the Flood began to take over the Truth and Reconciliation on 21 September.

In order to destroy the Pillar of Autumn and sterilise the Flood outbreak, John-117 and AI Cortana required Captain Keyes' Command Neural Interface, which contained the code for the Autumn's auto-destruct system. Initially arriving just outside of the control room, John had to escape from a seemingly infinite number of Flood attackers in a locked-down part of the ship by jumping out of it; a pool of the ship's reactor coolant broke his otherwise fatal fall. Returning up the gravity lift, John searched for an open door for the control room. The Captain managed to hold onto his humanity long enough to communicate with John via a UNSC comm system, confirming his survival. However, his orders to leave him and escape were taken less seriously and thought of by Cortana as evidence of being mentally disturbed.

Finally reaching the centre, they found that they were too late: Keyes had fully merged with the calcium blob and became a part of the Proto-Gravemind. With no other option, John punched through the former Captain's head and took out the neural interface. The two commandeered a Banshee piloted by Covenant Special Operations personnel and headed straight for the Pillar of Autumn's crash site.