From Halopedia, the Halo wiki
7 Echo 3 was a civilian transport craft. It, along with other transports, was used to evacuate both soldiers and civilians from New Alexandria during the Fall of Reach. The ship was initially pinned down by a Covenant corvette with Covenant attacking 7 Echo 3 to get at the passengers inside at one point breaching the craft's landing bay. However SPARTAN-B312 was able to use missile batteries to disable the corvette, allowing 7 Echo 3 and two other transports to safely take off.
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