Experimental MIRV

The  is a unique Fat Man launcher that can be found in the bomb shelter area in the National Guard Depot on a table near the remains of the skeletons of the Keller Family, who play a central role during the player's acquisition of this weapon. This weapon is clearly and without a doubt the strongest weapon in the game, though excessively so.

Obtaining
The player must complete the unmarked quest Keller Family Refuge before they can gain access to the secure section of the depot housing the weapon. However, if you crouch by the terminal and the bunker door, go into 3rd person, and rotate the cursor above the characters head and find the "Electrical switch button". This is not hard and works perfectly after about a minute. It's small but easy to find.

Background
MIRV is a military term for Multiple Independent Reentry Vehicle (or Multiple Independently Targetable Reentry Vehicle). It is a collection of nuclear weapons carried on a single intercontinental ballistic missile (ICBM). Using a MIRV warhead, a single launched missile can strike several targets, or fewer targets redundantly. The MIRV system was developed throughout the middle of the 20th century, and one of the main ideas behind the weapon system was to take out an enemy country with a single missile attack before the enemy nation could be able to respond.

Bugs

 * You can enter V.A.T.S. if you have fewer than 8 rounds. It will 'click' 8 times over the course of 20 seconds then exit V.A.T.S. with no action point loss. This can be used for a kind of short term god mode (useful if you're standing next to burning cars, for example).


 * Sometimes, on the Xbox 360 version of the game, NPCs in towns attacked with the MIRV remain hostile after reloading the game. The best way to prevent this is to save outside the town, enter it, blow it up, and load the save. If it happens, rebooting your console may help, as it will clear all data in your console's RAM.


 * If you have the MIRV and around 200 mini nukes (arbitrary amount spawned) and you turn on God Mode, it glitches the gun so it never needs to be reloaded - you can then fire round after round and have a barrage of missiles fly out non stop. However this can work towards any weapon, and is considered a bug of the game, not this particular weapon.

Entertainment Value

 * For the PC version, open up console and enter "TGM" to toggle god mode, granting unlimited ammo (and removing the need to reload any weapon), invincibility and other fancy stuff. You can get over five shots before the first ones detonate. Use your imagination.
 * Standing on a ledge and firing the MIRV at your feet will launch your character's body (corpse, to be more specific) spinning ludicrously high, sometimes even allowing you to see the outer edges of the map.
 * Try spawning 10 or 20 Super Mutant Behemoths, and let rip with the MIRV.


 * If fired in the Rivet City market it will launch the player through all of the steel walls to the outside and may cause the game to freeze (but it is still worth the hilarious two seconds).

YouTube Videos
left|Keller Family Tape #5 and the Experimental MIRV

Using the MIRV Skj1jN0oF24

Using the MIRV on godmode dgdQF_ZeUe4