The Fat Man was conceived, developed and tested inside the Fort Strong armory in Boston. The barracks were leveled and several houses were constructed around the fort to provide a testing area, to better ascertain how much damage the weapon would cause in an urban environment.
In June 2075, 布羅克將軍, the commanding officer at the fort, was placed in charge of developing M42投射器和測試剛生產的一批T-51B動力裝甲，並把成員分成兩隊，同時進行兩項計畫。The team in charge of the launcher first attempted to lower the weight of the warhead, and later tried to increase the power behind the firing mechanism, but both designs failed to produce satisfactory results. In both scenarios, 它的殺傷半徑超過了它的射程，搞死那些士兵in the blast or soaking them in lethal levels of radiation.
After almost two years, and the loss of a testing squad due to a misfiring weapon, the engineers behind the project 將fusion sub-charge內建於彈頭裡，大大的增加射程。 In September 2077, the launchers were shipped from the fort to a supply yard in Mississippi, and from there to the Chinese front.
The M42 Fat Man is an effective mortar/artillery weapon, allowing a person to bombard a large area with good precision and deadly force. 使用迷你核彈發射，爆炸影響的區域會有輻射性。
Although highly similar to the Fat Man, 實驗型MIRV一次發射8顆迷你核彈，成為一款極具破壞力and with a bigger blast radius的武器。
Esther is a unique Fat Man with a different rear mechanism, a blast shield, a light-blue body, and a thick glass or plastic bed holding the mini nukes. It weighs 10 pounds more than a standard Fat Man, but does not jam, and is more powerful.
The Striker was made by the employees of Beaver Creek Lanes for Thomas Davis, a former league champion that became handicapped after a battle injury. The Striker was meant to serve as a tool for Davis to launch bowling balls even though he had lost use his legs. It doesn't launch nukes but modified bowling balls.
This unique Fat Man was hidden by John-Caleb Bradberton, the inventor of Nuka-Cola in Nuka-World. Instead of regular mini nukes it launches Nuka-nukes, a specially modified, quantum-enhanced version with increased explosive power.