Getting the Blue Key (7)

Entrance: As soon as you start the level and get off the elevator, make a run for it to the right. Slam that door shut behind you! The entrance room is crawling with Sentry Drones, and you don't want them getting the drop on you. Once they've all blown themselves up, you can safely go back in to grab a Chaingun Cannon and a Small Medikit.

Armory: Moving into the next area, a door on your right will pop open, unleashing six Sentry Drones. These guys are easy targets for your RPG, so take 'em out. Watch out, though, because an Enforcer is also going to show up and try to ruin your day. Inside the armory doors, you'll find some RPG Ammo. Near the armory itself, there's a hidden compartment in the wall with a Freezer. Hit the switch there to open up the door where those Sentry Drones were; inside, you'll find a Portable Medikit and some Shotgun Shells. Closer to the elevator you're near, there's another compartment holding Pipebombs. Now, in the door right in the center of the room, you'll see a Forcefielded window. If you go through there, two Troopers will spawn. This room also contains a Pistol, Chaingun Cannon Ammo, and another Small Medikit.

Left Elevator: Head down the elevator. Be ready, because the door is going to explode, forcing you to crawl through the opening. Follow the path downwards until you reach a small nook containing an Atomic Health. You won't be able to grab the other two Atomic Health items behind it just yet. Keep going a bit further, and you'll find a shotgun. Look under the door near the shotgun – that's where the Blue Key is hidden! You can jump onto the ledge with the shotgun to grab some Body Armor. Follow that around to the rotating column. Nearby, you'll find two Large Medikits, and tucked away in a cranny close to the rotating column is a Laser Tripbomb.