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The Fat Man is a ranged weapon in Fallout 76.


The M42 Fat Man was developed at Fort Strong near Boston, Massachusetts. Development began in February 2076, with the goal being the development of a man-portable tactical nuclear launcher easy enough for use by troops on the ground, to destroy reinforced and entrenched positions.[1][2] Problems manifested instantly, as warheads were simply too heavy to clear the blast radius fast enough to provide safety for the operator. Even stripping them to the minimal possible size failed to produce an acceptable effect. Instead, the development team decided to increase the power of the launcher unit, even considering using railgun technology to accelerate the warhead. The notion was largely academic, as it would require for the overburdened soldier to carry an additional power pack the size of a suitcase and turn the Fat Man into a crew-served weapon.[3] Concurrent development ran on the MIRV version of the launcher. Live-fire testing claimed lives, in fact, with two soldiers killed during a test. No remains were recovered and the commanding officer in charge of the project, General Brock, covered up the incident, ordering his subordinates to send sand packed in an urn to their relatives.[4]

The project hit a breakthrough in December 2076,[5] when the project lead discovered a solution for the launcher problems. Six hours, fourteen cups, and one concerned night shift lab crew later, the future M42 launcher was conceptualized: Based on the spigot mortar mechanism, the launcher would only have to accommodate a firing through and system, relying on mechanical launching, rather than chemical or electrical means. The Fat Man warhead would be propelled by a sub-charge embedded inside the warhead, "catapulting" the warhead through the air to the target - giving plenty of range with the added bonus of not producing a smoke trail that could reveal the firing team to the enemy.[6]

By September 2077,[7] after one hundred test firings the weapon was complete and ready to be shipped to units overseas. A large number of units was manufactured and shipped together with the appropriate warheads to select locations throughout the United States.[8]


The Fat Man is a portable heavy weapon that launches mini nukes at distant targets in an arching trajectory.

If the Fat Man has the MIRV launcher mod, the Fat Man needs to be aimed such that the trajectory of the mini nuke reaches apogee above the target, as opposed to aiming such that the mini nuke hits the target or adjacent ground. When a MIRV mini nuke reaches apogee, it stops and splits into four projectiles. These projectiles fall straight down, detonating if they do not hit anything after falling 100 feet or 30 meters.

Weapon modifications

ModEffectsDamage changeFire rate changeRange changeAccuracy changeAmmo capacity changeAP cost changeWeight changeValue changePlanPerkComponents
Standard launcherAdhesive x2
Aluminum x4
Gear x4
Nuclear material x4
Screw x4
Spring x4
Steel x13
MIRV launcher-620+2.8+54Gunsmith 5Adhesive x5
Aluminum x7
Circuitry x3
Gear x5
Nuclear material x6
Screw x6
Spring x4
ModEffectsDamage changeFire rate changeRange changeAccuracy changeAmmo capacity changeAP cost changeWeight changeValue changePlanPerkComponents
Standard paint



Behind the scenes

"Fat Man" was the codename for the plutonium atomic bomb that was detonated over Nagasaki, Japan on August 9, 1945. With the exception of the tail fins, the mini nuke has a similar look to Fat Man.