I was told that the fat man is very good gun, but to go to the crater daleko.Est else?

There is an experimental Fat Man launcher at the national guard dept that fires 8 mini nukes at once. I believe it's called the Experimental MIRV and you need to find all the Keller Holotapes so you can get the code for the door to the safe.

Whoops i thought you were taking about Fallout 3 for a second.