Here we are in Hong Kong! This mission is very, very simple. Done a certain way, you don't need to lay a finger on anybody. You can always bop a few people, but there's an easier way of dealing with most of the troopers.
Aside from a thermoptic camo suit to hide you from the robots that emerge at the end of this mission, and maybe a hazard suit, I can't think of anything you'd need. So let's get going!
Activating the Gas
From your starting point, walk straight ahead and hop into the walkway under the floor. Walk straight and take the first left, which should take you into the armory. Aside from a key to the armory door, 2 multitools, and a datacube telling us how we can quickly and cleanly execute most of the workers here, there's nothing of interest. Return to the vent, and hang a left again, then take the first right. Hello, it's the fueling equipment, and to your left, a keypad! Let's try the code we got from the datacube, unless we feel like getting a little more personal. Oops, we've just released poison gas into the vents! Quickly get out of there, activating your environmental resistance augmentation couldn't hurt. To find a way out, backtrack to the walkway we entered from, and head south until you find an exit.
While we wait for the poison gas to work its magic, we can always head on up to the roof and get some supplies. We should shut down the camera first, check the east wall for a doorway, and a flight of stairs. As the gas was released into the lower levels, we should only head upstairs for now. At the top of the stairs, hang a left, and go into the room at the end of the hall. Check the wall to your left for a somewhat concealed cupboard. Open it one way or another, and pick up a master key for the lockers at the barracks. There's also a DataCube containing the security login and password. Use it on the security terminal, and read the other DataCube here, then return to the ground level.
Directly opposite the stairs is the ladder leading to the roof, climb up and ready your crowbar. Activate your ballistic protection and combat strength augmentations, then charge the two troopers up here and pound the shit out of them. (If you turned the turrets up here over to your side earlier, they'll be flat on their backs already.) Go to the crates next to the alarm panel, opposite the ladder, and when you crack open the crate, you'll discover some swords. Nice! Throw away your knife and your baton, assuming you still have them, in favor of one of these babies. There's also some wine, soda, and beer up here.
If you decide not to use the gas, approach the main door to the barracks, make sure the soldier patrolling the bathroom is not heading towards you and prepare for some precision sneaking. First, approach the first guy to your right and take him out from as far away as possible; this means you'll probably want to use a sword, surprisingly the other guys in the room don't give a damn about their colleague falling over with a blood-curdling scream. Carry his body outside, then enter the bathroom and dispose of another trooper. Turn around and approach the man at the computer, using pillars to hide from the others; this time you'll probably want to take him out from point-blank range. Go back to the entrance (you'll probably have to walk through the bathroom again or use the vents to avoid getting seen), sneak up on the last three fellows and take them out before either of them has time to start shooting at you.
One way or another, once the barracks are purified, head in. If you used the gas, there will be one one MJ12 trooper still alive, sitting with his back to you, making it very easy to slit his throat with your newest toy. Head into the bathroom, and search the lockers. You'll find a candy bar and a med kit in them. Leave the bathroom and take the stairs to your left up to the bunks. Use the sword to break open the locked lockers, by the time you're finished you should've found 150 credits, a munitions bay door key, a flight control deck key, the code to the elevator leading to the market, (which we'd only need if we wanted to come back here) and a multitool.
Return to the top of the stairs, but this time, hang a right. Go into the room at the end of the hall, unlock it, and check the wall to your right. There's another concealed cupboard here, on the other side of the white screen, containing 2 biocells. After picking them up, push the weapons lock button. Get a suit of thermoptic camo readied, and go down to the ground level. Head south, but not too close to the blast doors, and watch the doors to the left of them. When they start to open, activate the suit, and run like hell to the blast doors after the missile blows them apart. You should be able to duck under the rubble in the doorway and get past the electricity without getting killed, and you should also be able to make it into the elevator before the suit dies on you. Well, it's off to the market for us!