From Halopedia, the Halo wiki
Camber was a major manufacturing center for UNSC Navy fleet materials. As such, it held critical importance to the UNSC war effort and maintained its own grid of Orbital Defense Platforms as well as a formidable defensive fleet. At some point during the Human-Covenant War, Camber was attacked by a Covenant fleet led by Thel 'Vadamee. 'Vadamee and his fleet caught UNSC forces completely unprepared, the battle quickly resulted in a Covenant victory. Only 81,313 of Camber's 5.6 million population survived.
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