Defend O'Neal while he opens an exit | Mission 1: Distress A: CM Guide

The task isn't any different from the battle you've fought on the first level. Same as before, I recommend mostly the shotgun (preferably the one you've just acquired), unless you have ammo for the grenade launcher or any other similarly powerful weapon. Try not to move too far from O'Neal and use the flashlight to spot the aliens quickly. Don't spare your ammo and by any means necessary don't let the Xenos use melee attacks against you too often.