From Halopedia, the Halo wiki
During the evacuation of the city during the Fall of Reach, 7 Delta reported it as the location of a Covenant communications jammer to Catherine-B320 before being abruptly cut off. SPARTAN-B312 arrived at the center, finding all the troopers dead, (except for one), Noble Six found and destroyed the jammer but was quickly attacked by a swarm of Yanme'e. Kat, realizing it was a trap, ordered Noble Six to immediately evacuate the center.
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