Transit Hangar

Move to the hangar and kill the soldiers you find there.  Enter through the door and kill the soldier inside.  Go to your right and you'll find some sniper ammo.  Go back and through the door to the left of where you entered the hangar.  Kill the soldier before he can hit the alarm.  Continue through the open door and watch for a soldier hiding around a corner.  Continue into the next room and then across into the next.  Kill the soldiers and then use the computer.

Continue to the next hall and watch for smaller things.  Go through the door that you reach and be ready to kill the soldiers beyond it.  Watch for more soldiers coming from an elevator.  Look for a medikit dispenser and leave the trapped thing alone.

Continue to the next hall and kill the three soldiers there.  Go through the door at the end and kill the soldier behind it.  Go through the doorway near the base of the ramp.  Kill the soldiers shooting at Powell.  Give him a weapon and then have him fix the broken panel for the cold storage, where you'll find a couple of small things and weapons and ammo.

Exit and continue down the hall, pass through another door, and then head left.  Watch for a soldier around the next corner you come to.  Grab the extinguisher and then go through the far door and head downstairs.

Watch for small things and when you reach the bottom of the stairs search the body.  Pass through the doors and order Powell to fix the controls for the next door.  Continue until you see some oil drums - shoot them to kill hidden things.  Continue on into the next room, where you'll find some soldiers.  Collect the weapons and ammo in the room. 

Head down the hallway until you reach another room.  Order Powell to fix the save station and save your game.  Go to the door at the other end of the room and be ready to throw some flame grenades in as there are several things on the other side.  Enter the room and look for a key.

Use the key to open the locked door and you'll find some C4.  When you take it, soldiers will begin to come down on you, so you must fight your way back to the door where you entered the hangar.

When you reach the room with the third large thing you'll encounter, kill it and have Powell repair the broken door.  You need him to go into the room it opens to, but hit him with adrenaline first.  If not, he will break down on you.  Once he's in the room order him to repair the broken terminal.  This will give you a code to a door with a launcher and some grenades - as well as a save spot.

Continue on your way back to the entrance, watching for more soldiers.  Once you exit the hangar you'll exit the level.