Combat Team Alpha
From Halopedia, the Halo wiki
"Alpha" was stationed aboard the UNSC Pillar of Autumn in 2552. Following its arrival at Installation 04 and the ensuing space battle, Covenant boarders would breach the Autumn on port decks three and nine. Combat Team Alpha would engage these boarders, before later linking up with Combat Team Charlie to report heavy fighting on decks five through nine. Eventually, Captain Jacob Keyes would initiate a general evacuation of the ship, ordering combat teams Alpha through November to evacuate. Combat Team Sierra through Combat Team Victor evacuated after them.
Combat Team Alpha's fate upon Landing on Installation 04 is unknown, though it is likely that any survivors were part of the battalion led by Major Antonio Silva later in the conflict. By the time of the destruction of the ringworld three days later, Combat Team Alpha (along with all other local UNSC and Covenant forces) was killed.
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