From Halopedia, the Halo wiki
4 Charlie 27 was the call sign of a UNSC Army trooper from 4 Charlie stationed in New Alexandria during the Fall of Reach. During the Siege of New Alexandria, 4 Charlie 27 and his unit were sent to Club Errera in the Vyrant Telecom Tower to destroy a Covenant communications jammer, but became pinned down by a group of Mgalekgolo. SPARTAN-B312 was able to kill the Mgalekgolo and complete the team's mission.
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