The Big Boy is a unique weapon in Fallout 4.


The Big Boy is a Legendary Fat Man with the Two-Shot prefix, 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. Also, the cost of this weapon is high, at around 14,000+ caps with no Charisma and charisma related perks or effects.

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 being having to actually craft the Nuka-nuke ammo for it.

Weapon modificationsEdit

Slot Mod Description Weapon prefix Perk needed Components Base ID
Launcher Standard launcher Standard. 4x Adhesive
6x Aluminum
6x Gears
4x Nuclear material
5x Screw
6x Spring
9x Steel
MIRV launcher An experimental modification. Experimental MIRV Gun Nut 4
Science! 4
9x Adhesive
11x Aluminum
5x Circuitry
8x Gears
6x Nuclear material
8x Screw
7x Spring



Can be bought from Arturo Rodriguez in the Diamond City market. Also (rarely) dropped from legendary enemies.


  • 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 ten 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 twelve individual mini nukes.[2]


  2. Legendary_weapon_effects