Hidden soldier in Cairo Station

In Halo 2 the level, cairo station, There is a hidden man. All the way at the very last part of the level where the covenant bomb is being guarded by a herd of grunts and elites. Right when you exit the elevator take a left. Then take another till you are at the very back of the room. There you will see a fellow UNSC soldier holding an SMG. You can keep pushing him by walking into him. If you push him close enough to the covenant enemy he will join you in combat.