Stay in the duct. There are two enemies, one a commander, on a catwalk across from you.
Hitshot these guys with the pistol.
There are two guys talking down and to the left of the duct exit, you can just see one from the duct. But jump down amd silently kill these two.
Now there is a patrolling heavy on each side to dodge. I stayed on the left. A patrolling henchmen will stop on the stair landing leading up to the last commander.
There is a concrete pillar and junk to hide from the heavy, headhsot that guy and wait for the heavy to go back on patrol. (He heard the shot and "investigated" for a bit, but I easily hid at that pillar.
Then as the heavy patrols back, go up the stairs and kill the commander.
Now, pull the lever and open the door. A couple heavies and a couple normal enemies will come through. I simply stayed up in the control room with dual sturmgewehrs and killed the enemies as the came up. The heavies will stay at the doors, a couple normal enemies will come through but shouldn't be too hard. Keep in mind there are now two doorways into the command center! But most enemies are towards the level start side, so come to that door.