Complete section corresponding NSM
While transferring to this area, if you've followed this walkthrough well, you'll run into a convoy. No biggie, right? Again, use the wide cannon if you're nervous. But you have a few health dots now, so it should be no problem.
At the beginning, you'll meet a type of guy I call "bionic dude." He tries to trick you by going up and down as well as left and right. Here's the way to beat him, though. It's known as the "bionic maneuver."
Basically, as shown above, you hook straight up and shoot as you drop. He'll move up right into your shot. Head right. See the single brick jutting out of the ceiling? Swing diagonally off it and land on the right to get the free man (there's another amusing way... but I won't tell you here.) Fall down facing right. If you're good, you can shoot just before you land and kill the bionic dude at the bottom. Otherwise, move to the left and use the bionic maneuver. Swing over the crate and go right until you're stopped by the spikes. Hook straight up a few times until you're at the top platform. Swing to the right, and kill the bionic dude. Bounce off the springs and grab the platform above. Hook up a few times. Then position yourself like in the second picture, right under that small safe spot. After the mine cart passes under you, keep hooking up quickly all the way to the top, then run right. Keep going, swinging over gaps as necessary. Fall down when you need to, and you'll come to the place shown in the third picture. Fall down and grab it, as shown, then keep going right until you're at the place in the fourth picture. From there, keep hooking up. Then move to the left and keep hooking up. You'll find the boss door. But before you go in, know that right outside the boss door is a good place to gather bullets. Just kill all the parachuters.
The boss is nothing special, just a platoon again. Finish it up!
Note: At this point, you can go to Area 17 if you wish, but there's nothing useful there.