Outbreak at the Containment Facility

Several battles in the Containment Facility were the turning point of the UNSC and Covenant's involvement in the Battle of Installation 04, where the two sides proved unprepared for a third enemy: the Flood.

Prelude
During the ongoing campaign for control of Installation 04, the Covenant had gained control of the containment facility and accidentally released the Flood. While the upper levels were cleared, the lower levels were infested and some Sangheili commanders were lost in the process.

After being informed by a captured Sangheili that the facility held weapons, Captain Jacob Keyes, along with 2nd Squad deployed to investigate the structure, expecting to find a weapons caché that could be of some use against the Covenant. They landed on the D77-TC Pelican dropship Victor 933 and proceeded to infiltrate the structure. They later met up with Staff Sergeant Avery Johnson's "Fireteam Charlie", who followed behind in their own Pelican.

The raid
While exploring the facility, Keyes' team eventually came across a sealed door which had been locked down by the Covenant to prevent the escape of the Flood. With increased curiosity, Keyes ordered that the door be opened. Finding nothing sinister about the room initially, some of the men become nervous when they head a strange hissing sound followed by Second Squad - who were exploring a lower level - reporting that something "not Covenant" was "tearing" through them. They would soon encounter what that something was, as a number of Pod infectors broke through their containment cells and began to attack the team, attempting to convert them. Private Wallace Jenkins was latched onto by one of the infectors, and rapidly succumbed to the infection. The now-combat form was fired at by Johnson, but ultimately succeeded in knocking him out of the room. Johnson then proceeded to run away from his now-infected comrades, being fired at by shotguns and assault rifles before managing to escape across an energy bridge, just as the bridge was deactivated by one of the combat forms. Johnson threw some grenades behind him to destroy the pursuers, before finally escaping up the primary elevator out of the facility.

Of the team, only three escaped conversion - Sergeant Johnson, who managed to leave the room in time; an unnamed marine who "played dead", and Mendoza, whose corpse was abandoned by the parasite.

Meanwhile, a crashed Spirit dropship in the swamps was commandeered by the Flood, who used it to escape the ringworld and attack the Fleet of Particular Justice's ships.

Arrival of John-117
Simultaneously to the raid, Spartan John-117 had been fighting to gain a control of the ringworld's Control Room. Having accessed the facility with Cortana, the AI warned John that Keyes' raid on the weapons cache was a mistake and urged the Spartan to find him before it was too late while she remained in the computer systems of the facility. The Spartan departed the Control Room alone, and was transported to the swamps of the containment facility by Echo 419, landing near Victor 933 ' s crash site.

The Spartan proceeded to progress up the swamp, following the route earlier taken by Fireteam Charlie while being watched by the Flood, whose Marine IFF transponders flickered on and off the Spartan's radar. Entering the facility, the Spartan found many dead bodies and rooms of gore, but no life to speak of except one Marine survivor armed with an M6D magnum, who attempted to shoot John out of fear. After entering the containment room, he found Private Wallace A. Jenkins' helmet, which contained a built-in video camera. After seeing the gruesome events through the eyes of Jenkins, the remaining Flood spewed out of nearby doors. John-117 proceeded with the remainder of Second Squad, combating infection and combat forms in the open, after being advised by Foe Hammer to take refuge at a tower out in the swamps.

The survivors went through the swamp in search of a tower, which was their designated evac site for Echo 419. After making it to the structure, the Marines were aided by a mysterious ally - floating constructs known as Sentinels. The Sentinels, commanded by the Monitor 343 Guilty Spark, defended the humans, eliminating any Flood in the vicinity. The Monitor then teleported the Master Chief to it, referring to him as "Reclaimer", and then taking him away with him to the Library.

List of appearances

 * Halo: Combat Evolved
 * Halo: The Flood
 * Halo Graphic Novel
 * Breaking Quarantine
 * Halo: Combat Evolved Anniversary