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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 took place in caverns underneath the facility in the Forerunner structures. 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, and Sangheili, as well as several Banshees 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.
When the Pillar of Autumn was attacked above the Halo by opposing Covenant forces, 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. While some of the ODSTs were able to attack the butte with supporting air support, some were lead into what was known as a back door. After elimination of all immediate threats, this team entered the back door and took a lift to regroup with the rest of the squad. It is unknown how much of a defense Silva put into guarding this pass, but apparently the Covenant were unable to use this backdoor to gain access to the base.
Despite now having this strategic foothold, Silva still had a great deal of problems. The ODSTs were equipped with enough food and supplies to last 2 weeks. However, that was not the case with the 63 crewmen that John-117 was able to rescue. Also, the dropships were running low on fuel and the base was not adequately prepared for a massive counter-attack. Therefore, Silva ordered McKay to go to the downed Autumn and recover whatever supplies that she could. The raid was a success and only a minimum of UNSC casualties occurred, while several Ghosts and a Spirit dropships were destroyed. The Marines and ODSTs were able to secure a sufficient amount of fuel, food, and munitions. Also, two 50mm turrets were recovered, a contingent of LRV Warthogs, and 4 Scorpion Tanks. Unfortunately, there was no ammo or rockets for the Pelicans, limiting their usage to transport only. Some of the supplies, LRVs, and Marines were lost in the return trip due to Covenant resistance.
It was later discovered that the Flood had been attempting to break into the base and were only impeded by a single metal grate-which they had already used hundreds of Plasma Weapons on-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.
The base was destroyed, along with Installation 04, when John-117 overloaded the Pillar of Autumn's reactor.
The defenses of Alpha Base consisted of UNSC personnel that survived the crash of the Pillar of Autumn. A number of stationary 50mm autocannons were in place and linked to the base's AI, Wellsley. The base had several makeshift landing pads where dropships could be docked and refueled in relative safety. Later, this position was reinforced by a group of LRV Warthogs and at least two of four Scorpion tanks that were recovered from the downed Pillar of Autumn.
Due to successful raids and the attack upon the Truth and Reconciliation, at least four Shades, were set up in defense of the base. Unfortunately, these turrets had limited effectiveness against dropships. Also, 15 operational Covenant Banshees were recovered. A basic perimeter was set up and monitored through motion trackers by Wellsley. Pelicans had quick strike teams in place if there was a perimeter breach that could respond in about two minutes. Finally, a combination of LRVs and captured Ghosts were used as patrols, effectively combining power and speed.
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.
- Two 50mm autoturrets (AI operated).
- High amounts of light and heavy weaponry (both UNSC and Covenant grade).
- Four Shade turrets.
- At least two of four remaining Scorpion Tanks, dug partially underground for protection.
- A contingent of LRV Warthogs.
- 15 operational captured Banshees.
- Captured Ghosts (estimated at about 5-10).
- AI Wellsley.
- Multiple landing pads.
- All surviving Pelicans, but these were low on machine-gun ammo and had no rockets.
- Ground based motion detectors.
- A system of trenches surrounding the base.
First Battle of Alpha Base
The base was attacked twice while during the time the UNSC was on Installation 04. This attack was led by Major Silva and his battalion of ODSTs in an attempt to wrench the protective butte from the hands of the Covenant in order to establish a place where the UNSC personnel could regroup. Silva ordered Lt. McKay to lead an assault through a pass that hopefully led to the top of the base. As McKay and her company began their climb, the Covenant launched a preemptive strike against Silva. Wellsley informed him that the attack would consisted of an estimated 100 Ghosts.
With half of his forces committed elsewhere, Silva ordered Companies A and D to group into an infantry square. This, and the natural terrain, gave the ODSTs a better chance of survival against the Ghosts' fixed weapons. At the start of the battle, the Covenant fought very poorly, with several Ghosts firing upon each other or colliding in their haste to score a kill. Eventually, a Field Commander took charge and ordered all of the vehicles to turn counter-clockwise and then to attack the lowest pit in the square. Human casualties increased and the square started to break. Silva responded by reinforcing the pit, bringing up heavy weapons to deal with the vehicles, as well as having his sniper team concentrate fire on the Field Commander. As an apparent afterthought, Banshees were thrown late into the fight and were quickly eliminated by M19 launchers. Finally, with the Field Commander dead, and a 50% casualty rate, the attackers retreated, some carrying extra riders on their Ghost. From that attack, 23 were KIA, 6 were critically injured, and 10 were WIA. Finally Silva could get the Pelicans to attack the butte and give McKay some support.
Meanwhile, McKay was making her way up the butte. She had already lost some of her soldiers, one to a plasma grenade, but she was making a good deal of progress. At last she made it to a back door into the structure. She fired an M19 rocket into it, which struck some sort of ammo dump, clearing the room of all hostiles in the process. She and her remaining company entered to find an elevator to the surface of the butte. As a result of the battle, the UNSC managed to secure location for a base of operations.
Second Battle of Alpha Base
- Main article: Battle of Alpha Base
The second battle was Zuka 'Zamamee's attempt to get into the base and kill John-117. Approximately 6 Spirit dropships full of Covenant and the captured Pelican Charlie 217 full of cloaked commando Sangheili participated in the attack. The Pelican managed to touch down and release the Sangheili before its landing pad was doused in fuel and lit. However, Zuka 'Zamamee and several Sangheili had already fled and began in search of John. Before being killed by the Stealth Sangheili led by Zamamee, a valiant crewman, Xaing Cho, gave the AI Wellsley control of the 50mm autocannons, with which he was able to eliminate 1 Spirit dropship. The remaining dropships released their troops further away from the base and attempted to assault it thus. Snipers expertly inflicted heavy casualties on the disembarking troops. Two of the recovered Scorpion Tanks had been entrenched and were able to cut down much of the onslaught, including the Field Master. With their leader dead, lesser Sangheili attempted to assume command with little success. In the end, all remaining Covenant were either captured, killed, or forced to retreat. Yayap and Zamamee were able to survive by stealing one of the Banshees that the Marines had been able to salvage.
- Wellsley suggested it be named 'Gawilghur', referencing a fortress Sir Arthur Wellesley, Duke of Wellington, laid siege to in India. Major Silva shot down Wellsley's request and stated that most of the Marines wouldn't be able to pronounce the name right.
- One of the said four Scorpion tanks is presumed to be the one encountered on Assault on the Control Room.
- Halo: The Flood (First appearance)