Plutonius

Before the Great War, Kansas City was a major nuclear launch site. After the city was hit by the bombs, the silo staff survived, but was turned into ghouls, who formed a town called Gravestone in the ruins of the city.

Plutonius is the only nuclear bomb left intact in the silo and the ghouls formed a cult which worships it. This nuke was later taken by the Midwestern Brotherhood of Steel and used to blow up the entrance to Vault 0 and gain access to the Calculator's domain.