Alpha Base (Installation 04)

Alpha Base was the main tactical Firebase 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. Wellsley tagged the base as HS2604.

The humans set up camp around the base using the supplies they had scrounged from the Autumn and their Human Entry Vehicles. They lived in Cubicles and ate mostly Meals Ready to Eat. A good deal of the activities also took place in caverns underneath the facility, in the Forerunner structures.

History
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 was attacked above the Halo, the ODSTs, under command of Major Antonio Silva, abandoned the ship aboard Human Entry Vehicles, and most of them landed around the base. Silva saw the tactical advantage to the butte, and ordered First Lieutenant Melissa McKay to take it.

The ODSTs were successful in taking the base, but they were under supplied. Silva then ordered McKay on a convoy to the Pillar of Autumn crash site, and she successfully gathered materials and resupplied the base. It then became the central base of the survivors of the Autumn, as all known surviving naval personnel and Pelican ships were relocated there.

Later, the base was 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 attacked the base in hopes of finding the Master Chief. The attack failed and the humans held the mesa. The surviving Scorpion Tanks were also used as a static defensive line having been buried up to their turrets with sand and dirt. Thus they were used as a stationary gun.

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

Trivia

 * Wellsley suggested it be named 'Gawilghur', referencing a fortress Sir Arthur Wellesley, Duke of Wellington, laid siege to in India.