Alpha Base (Installation 04)

Summary
Alpha Base was the main tactical base used by the remaining UNSC forces after planetfall on Installation 04. It was located on a small mesa several kilometers down-spin from the crash site of the Pillar of Autumn. The mesa itself housed a collection of Forerunner structures as well as a system of caves stretching beneath the facility and linking with the larger subterranean system of the ring.

The Covenant occupied this mesa when they discovered the ring, using mostly a light compliment of Grunts, Jackals, and Elites, as well as a few Banshees. 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.

When the Pillar of Autumn is attacked above the Halo, the ODSTs under command of Major Antonio Silva abandon the ship aboard Human Entry Vehicles and most of them land around the base. Silva sees the tactical advantage to the mesa, and orders First Lieutenant Melissa McKay to take it.

The ODSTs are sucessful in taking the base, but they are undersupplied. Silva then orders McKay on a convoy to the Pillar of Autumn crash site, and she sucessfully gathers materials and resupplies the base. It then becomes the central base of the survivors of the Autumn, as all known surviving naval personnel and Pelican ships are relocated there.

Later, the base is fortified with Shade Turrets, salvaged 50mm cannons from the wrecked Autumn, and sensor equipment operated by the AI Wellsley. These came in handy when Covenant forces led by Zuka 'Zamamee and Noga 'Putumee try to attack the base in hopes of finding the Master Chief. The attack fails, and the humans hold the mesa.

It is later discovered that the Flood have been attempting to break into the base and are only impeded by a single metal grate leading to an unnoticed group of caverns. The entrances to these caverns are sucessfully sealed, and the Flood are delayed from overtaking the base. By the time they manage to break through, the UNSC forces have abandoned the base in hopes of leaving the installation aboard the Truth and Reconciliation.