Brothers in Arms
From Halopedia, the Halo wiki
Brothers in Arms is a song included in the Halo: Original Soundtrack. it is number 3rd in the track list. The ending of which appears on the Main Menu of Halo: Combat Evolved, along with the ending cutscene to the level Pillar of Autumn.
It was remade into Follow our Brothers for Halo 3.
It runs for 1:31.