Sub-Aquatic Facility

After the first skirmish in the jungle area, you're going to come up to the heavily defended science building. Some of the enemies here will be dropping the carbine for the first time; this automatic rifle isn't as powerful as the SMG or the P90, thanks to the fact that it can't be dual-wielded, but it does have a scope and a suppressor on it, making it a decent choice for general engagements, especially when you're trying to keep things on the down-low. You also might run across a 9MM Automatic, a worthy addition to your arsenal, since it resides in your handgun slot and enables fully-automatic firing.

Assaulting the position will take a little luck, and a lot of health. Since you have your super speed now, though, you may be able to just bum rush the area and go in guns blazing, especially if you're packing dual SMGs. When you get close to the doors, more enemies will spawn in from the direction you came, forcing you to turn around and deal with them before you move on inside, but hey - you will have a machine gun at your disposal, so use it and try not to die. The doors won't open here until you manage to kill everything that moves, so it's not like you have much choice in the matter.

Through the Facility

Watch out for snipers in this area.

When you reach the interior of the facility, you'll come to a control room with a soldier inside, and will get more of that lovely ear-splitting (and health-reducing) alarm sound. You'll need to smash the window and shoot out the alarm from there. Alternately, you can break the grate on the vent and crawl through to reach the room itself, but that'll take a little while. There is armor inside, on the plus side.

When you're through the facility, you'll be able to crawl through a vent in a bathroom to reach another portion of the base. You'll have some tough fights in your path before you can reach the exterior; you'll know you're almost there when you reach the locker room and start hearing an announcement about requiring an amber passcard to reach the surgical ward. Since you'll need surgery to get your implant out, keep your eyes out for one of those.

Soon thereafter, you'll reach the pools of the facility, which are overwatched by a half-dozen snipers or so. Since you're probably running low on sniper ammo at the moment, you'll probably want to get up close and personal to take their weapons from them and fill back up on rounds, even if it does mean that you'll have to lose a bit of your armor supply. Alternately, you can just stay in the water and swim towards the end of the lake area, where there's a vent underneath the waterline you can pass through. You'll have to shut off the hot water switch to the right of the path first, though.

Science Wing

When you reach the first fork in the road past the locker rooms of the Science Wing, you'll be able to head left to reach the surgical ward, although the door is currently locked. The Amber passcard that you require is located down the right hall, past the autopsy bays and the science lab. Grab it, then return to the science wing to finally get your little implant out.

When the operation's over, you'll find that you've...changed...again. Alarms no longer seem to hurt you, thankfully, but all of your equipment has been removed, leaving you with only your claws for company. Making your way out of the science wing will require you to blast through a couple of soldiers, then swim out through one of the access tubes in one of the nearby rooms.

Outbreak Outbreak Outbreak!

These mutants aren't that much more difficult to kill than normal mercs, though they do deal slightly more damage.

Well, as you'll soon discover, Krieger's experiments have come back to haunt him, or at least haunt the highly-trained mercenary forces he's hired. The mutated men will quickly break out of their containment cells after you escape from the facility, and start causing all kinds of P90-fostered trouble on their guards, which you'll be in the middle of. It's all-out war between the freaks and the mercs, but everyone's still gunning for you, so you're not going to be able to pick sides.

When you sneak up on a firefight, let it play out before you deal with the survivors, as it'll give you fewer targets to worry about. All of the mutants will be wielding P90's, so you should be able to rack up a good amount of ammo for that weapon, especially if you use your feral attack to do most of your killing. Your regenerative properties seem to have been increased a bit, so you'll be gaining health back much more quickly than you were previously, at least when you're near enemies. If you start to fill up on P90 ammo, though, feel free to use that instead of your Feral attacks. The mutants can take a bit more damage than the normal mercs, but still go down relatively easily.

Keep moving through the fences and you'll eventually reach a wall on which some mercs are attempting to hold back the barbarian horde. The machinegun here seems to do more damage than is normal for an emplaced weapon, so just run up to the wall underneath it as quickly as possible before climbing the ladder to get on top and kill the mercs.