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Fallout Wiki

The Big Boy is a unique weapon in Fallout 4.


The Big Boy is a Legendary Fat Man with the Two-Shot effect, allowing it to shoot two mini nukes at once for the cost of only one, giving it the most damage potential from a single shot in the entire game, with the sole exception of the nuke, which is obtainable only through console commands.

The Big Boy is compatible with the MIRV launcher mod. The Big Boy will shoot twelve[1] mini nukes, while only consuming one. The blast radius of this weapon's mini nukes is substantially larger than normal and that the nukes lose their momentum and fall to the ground after splitting. In addition, the cost of this weapon is high, at around 14,000+ caps with no Charisma and related perks or effects, making it one of the most expensive weapons in the base game.

It is also compatible with the unique Nuka-nuke launcher's unique modification, meaning that one can effectively do double the damage of a regular Fat Man, and 50% more than the regular Big Boy, the only downside is having to actually craft the Nuka-nuke ammo for it.

Weapon modifications

ModDescriptionWeapon prefixDamage per shot changeFire rate changeRange changeAccuracy changeMagazine capacity (shots per reload) changeWeight changeWeapon value change in capsEffect(s)Perk(s) requiredComponentsForm ID
Standard launcherStandard.Adhesive x4
Aluminum x6
Gears x6
Nuclear material x4
Screw x5
Spring x6
Steel x9
MIRV launcherAn experimental modification.Experimental MIRV-450+5.3+138Gun Nut: 4
Science!: 4
Adhesive x9
Aluminum x11
Circuitry x5
Gears x8
Nuclear material x6
Screw x8
Spring x7



The Big Boy can be bought from Arturo Rodriguez in the Diamond City market.


  • The Big Boy with the MIRV mod will shoot 12 mini-nukes due to both of the mini-nukes fired each splitting into 6. If they fly a certain distance they will disperse into 12 bomblets.
  • Due to the way that the legendary Two Shot prefix is programmed, the MIRV nukes will have a much larger blast radius and damage, comparable to 12 individual mini nukes.
  • When applying the Striker's unique Bowling ball launcher onto the Big Boy it will actually result in one "gaining" modified bowling balls, as each ball can be retrieved individually.

Behind the scenes

Its name is in reference to "Little Boy," the atomic bomb that was released above Hiroshima, with its counterpart "Fat Man" (the name of the weapon type) being released on Nagasaki three days later; actions that, in the Fallout universe, ultimately foreshadowed the end of civilization.