Experimental MIRV

The  is a unique Fat Man 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 deals the most damage in the entire game. It is strange to wonder why the national guard depot would be chosen for the storage location of such a weapon. It is clearly in experimental stages, and is quite ironic that a nuclear rifle would find safety and salvage stored in a nuclear fallout bunker.

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.

It's also possible to gain entrance to the armory by using a glitch, see National Guard Depot for details. Just go into Third-Person View, and move your analog stick [or mouse] and look for a different activation line saying "Activate Electrical Switch". You can now get the MIRV without having to find the Keller Family Transcripts. The Electrical Switch will be slightly lower and to the left of the Terminal. A Glowing One will be found at the back of the cave/secret room who is probably Mr. Keller, the father of the family who took shelter in the armory.

Tips

 * When fired, this weapon causes massive damage in the form of eight Mini Nukes. The nukes take a random spread, usually 6 or 7 in a semi-tight group and one off in the distance. If aimed correctly, this weapon will most likely kill anything in one hit, even Super Mutant Behemoths.
 * You'll have to become familiar with how to properly aim, considering the distance and height of the mini nukes' flight. If you plan to use this, trying to use it like the Fat Man usually ends with a flash as a nuke hits the ground in front of you.
 * You should not fire or at least be cautious when firing up a hill or towards someone with obstacles in the way.
 * The MIRV looks identical to the Fat Man, which means that it really should only be able to fire one mini nuke at a time, but somehow 7 more appear from the weapon all the same.
 * If you pause the game just prior to the MIRV releasing the mini nukes, you'll see that the MIRV fires "one" mini nuke that splits into 7 identical mini nukes. This is due to the use of overlapping. All 8 mini nukes occupy the same spot until exiting the weapon.
 * The MIRV can be repaired with the Fat Man.
 * The MIRV actually does the same damage as a Fat Man per Mini Nuke. (12880/1610=8) This means that, technically, the MIRV is just a fat man with extra capacity and increased ammo usage. So don't waste your time or caps finding/buying 8 Mini Nukes if a Fat Man can do it with 1 or 2.

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.

For a good example of a MIRV, and possibly the real-world weapon this gun was based on, see the LGM-118A Peacekeeper ICBM system developed by the United States during the Cold War. It was capable of firing one missile which would 'birth' up to 10 nuclear warheads over a wide target area.

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. Since you only take 10% of normal damage whilst in V.A.T.S., 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.


 * Sometimes on the Xbox 360, a graphics error can occur when detonation is very close. It can cause large, black rectangles to extend from the weapon out to as far as you can see. A console restart will fix this.


 * Rarely, when you bring out the MIRV, there will be a Mini-Nuke stuck on the end of the weapon. This is purely a graphical anomaly, more likely to occur when using the console command 'tgm' (enabling infinite ammo, god mode, no reload), as this weapon was not intended for rapid-fire.


 * Also when firing the MIRV in V.A.T.S. at point blank range you lose very little health; this quality is shared by the Fat Man, where a V.A.T.S. discharge can result in loss of a small amount of health and sometimes a crippled body part. Be careful, though; the shots will still damage followers, and can also result with death with very little health.
 * Sometimes when carrying the Experimental MIRV attempting to enter Tenpenny Tower can cause the game to freeze. I suspect this is because tenpenny is involved for some reason with the MIRV

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