Fat Man (Fallout 3)

The Fat Man is a handheld tactical nuclear catapult, found in Fallout 3.

Appearances
The Fat Man appears only in Fallout 3, and can be found in the Rivet City market area. Because of its nuclear payload, it is by far the strongest V.A.T.S. enabled weapon in the game, perfect for taking out multiple enemies or heavily armored units - and in normal use, you'll be encountering both. The Fat Man has an estimated range of 150+ yards and will fall if shot in the air; be aware that the blast zone will be irradiated. You can find this gun right outside of GNR, as well, during the "Following in His Footsteps" quest by picking it up from a dead Brotherhood soldier. Using this method, one can acquire the Fat Man fairly early in the game. Note that this Brotherhood soldier must be killed by the Behemoth (mutant) you encounter during this quest.

A Fat Man can also be found in Evergreen Mills, there is a Fat Man dropped by Talon Mercenaries in the capitol building during or after the fight with the Behemoth (mutant), and another one is present at the Talon Company fort.

In the Armory at National Guard Depot, behind a door that requires a passcode,you can find the MIRV version of Fat Man which can fire up to 5 mini nukes at once.Requires finding all 5 keller diaries.