The Fat Man also can be known as The Big Boy is a Nukeual weapon that is featured in Fallout 3 and 4 it is also featured in the mobile game Fallout Shelter.
The Fat Man was named after the atomic bomb which the United States dropped over Nagasaki in 1945. To avoid controversy, it was renamed Nuka Launcher in the game’s Japanese version.
The Fat Man was conceived, developed and tested inside the Fort Strong armoury in Boston. Several houses have been constructed around the fort, to provide a testing area to ascertain how much damage the weapon would cause in an urban environment.
There are different types of the Fat Man that have been modified in the game by the developers as well as people also creating mods for them to for example fire chickens out of the gun.
Although highly similar to the Fat Man, the experimental MIRV fires 8 mini nukes at once instead of 1, making it more powerful and with a bigger blast radius but the downside to this gun is that you will be using 8 Mini Nukes at one time instead of only using one.
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. This was featured in Fallout New Vegas DLC Gun Runners Arsenal however people have modded the game on PC to get this Gun in Fallout 4 as well.