The humans set up camp around the base using the supplies they had scrounged from the Autumn and their Human Entry Vehicles. It was abandoned by the humans shortly before the destruction of the ring, due to their taking of the Truth and Reconciliation and the growing Flood presence in the area. The Flood used those cave systems to try and envelop the Human population on the base.
The Covenant occupied this mesa when they discovered the ring, using mostly a light compliment of Unggoy, Kig-Yar, Jiralhanae, and Sangheili, as well as several Wraiths to guard it. It provided a good view of the surrounding areas, and the steep embankments around it made it hard to reach from the ground. Strategically placed Shade turrets made the mesa hard to assault from the air as well.
The defenses of Alpha Base consisted of UNSC personnel that survived the crash of the Pillar of Autumn.
At its strongest point, the bases defenses were as followed:
- Battalion of ODSTs led by Major Silva.
- Most of the Pillar of Autumn's remaining crew that were not captured or in cryo stasis.
- High amounts of light and heavy weaponry (both UNSC and Covenant grade).
- Four Shade turrets.
- At least two of four remaining Grizzly Tanks, dug partially underground for protection.