Censorship in Japan
Bethesda Softworks made changes to the Japanese version of the game, changing the side-quest "The Power of the Atom", in which players in the non-Japanese version of the game are given the option of either defusing or detonating a dormant atomic bomb in a certain city. Non-playable-character Mr. Burke has been taken out of this side-quest, rendering it impossible to detonate the bomb and leaving the player with only the choice of defusing or ignoring it. Also, the name of the mini-nuke weapon Fat Man was changed as it was a reference to the bomb dropped on Nagasaki.
Info taken from Wikipedia