The yellow floating guys are back to help out. Stay back while they attack, and gather up the loot when they're done. Once again you head down into a trench to go along the long tunnel. When you come up there's a firefight between the yellow guys and the bad guys. Hide down in the tunnel until they're done, otherwise you'll get zapped. Then come out and gather up loot.

When you come up, go down to the end fo the blue corridor. The blue floating ball says to wait there, and of course there's a massive attack. Fight through it. Soon you hit another elevator.

Master Halo Walkthrough