Second Base
From Halopedia, the Halo wiki
Second Base, along with Green Hills, was one of two colonies lost directly after Harvest. Initially, the UNSC had hoped to cover up their loss by explaining it away as a communications blackout caused by Insurrectionists. Eventually, they revealed that the UNSC was now fighting a xenocidal alien hegemony, and that this and another colony had been destroyed with the total loss of two million civilians between them.[1]
