Brothers in Arms is a piece included in the Halo: Original Soundtrack. It is the 3rd piece of the album.
The ending of the song appears on the Main Menu of Halo: Combat Evolved and the opening and closing cutscenes of The Pillar of Autumn. It plays twice during the level Halo; once during the Covenant's last attempt to eliminate the first group of survivors, and again on the Covenant's attempt to kill the very last group of survivors. It also plays four times during the level The Truth and Reconciliation, once outside the ship, once when entering the loading bay, once near the brig where Captain Keyes is being held, and during the ending cutscene. It also plays in the Shuttle bay if all, or nearly all, of the Marines are dead, when Cortana will call Echo 419 for reinforcements; opening the bay will cause the song to play. This song's ending is exactly the same as the opening to the Halo 2 track "Impend."
The first time the song plays is when John-117 and Cortana abandon the UNSC Pillar of Autumn, and its tone is suitably martial for the situation. It opens with a synthetic drum beat; starting at 00:06, the melody of the piece begins on the flute. At 00:32, the melody segues over to strings, who continue the piece's main motif an octave lower. They are shortly joined by a fanfare on synth organ. At 01:00, the drums fade out, allowing the strings and flute to slow the tempo and bring the piece in for its serene conclusion.