At the beggining of the level, after the snipers shoot through the window, there are the people coming out of the hall. There are 2 nova6 tanks in each corner after they come through, there are also two more right in front of the table that gets tipped over.

Throw 2 grenades at the ones in the back, shoot the ones in the front (this may take a while). It can be quicker to blow them up if you pick up the Kiparis ACOG on the ground (the one guy drops.

Then before you go up the little ladder there is an intel device and a radio. Pick up the intel and turn the radio on with X.

Then go do the other part till you jump off the roof in slow-mo. T here is a radio in the room behind the fridge on a dresser. Turn it on.

Wait about 5-15 seconds and you should here a strange noise. The walls will shake, and there will be a noise like a cha-ching.

Then the Thunder Gun will be sticking out of the wall. You will also be able to get a Grim Reaper when you are near the end before Dr. Steiner dies in the area where the HK21 Drum Mag is.