Experimental MIRV

The Experimental MIRV Fat Man Launcher can be found in the bomb shelter area in the National Guard Depot Armory next to 5 Mini-Nukes on a table near a Glowing One near the remains of the skeletons of the Keller Family. When this weapon is fired, a random shotgun spread seems to be the path they take, usually 6 or 7 near each-other and one off in the distance before impact, if aimed correctly, this weapon can kill anything in 1 hit, even the Super Mutant Behemoth. You must have obtained all five of the Keller Family Transcript's before you can gain entrance to this part of the room. It fires 8 Mini-Nukes at once and if you have less than that it will just make an error sound telling you that you do not have enough ammo.

In appearance, it looks like a rustier version of the Fat Man.

-- Be sure to never use this weapon at close range or near NPC's wished to be kept alive. --

Bugs
If you have less than 8 rounds, you can still enter VATS to attack. However, it will just 'click' 8 times over the course of 20 seconds, then exit VATS with no action point loss.

Cheat
For the PC version, pressing Console and entering "TGM" will toggle god mode, which also grants unlimited ammo (no need to reload). You can get 5-6 shots off before the first ones start detonating. Use your imagination.