From Halopedia, the Halo wiki
7 Delta was a UNSC Army unit stationed on Reach during 2552. During the Fall of Reach on August 23, they fought in the Siege of New Alexandria, where 7 Delta 19 and his team failed in destroying a Covenant communications jammer located at the Sinoviet Center. Only one of the unit's men survived, and became severely traumatized by the deaths of his entire squad. By the time SPARTAN-B312 arrived some time later to complete their mission, the survivor was cowering in a corner, pointing a gun to his head and screaming nonsense.
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