Sometimes bombs don't go off. Did the US have any contingency plans in place to destroy or even recover the atomic bombs they dropped on Japan, in the event they failed to detonate?
To my knowledge they never codified the plans though they thought about the possibility and took pains to avoid it:
With the Little Boy bomb, the sheer fact of it hitting the ground was probably likely to cause a chain reaction, because of the sheer amount of fission material inside of it. Even if it had not detonated at full strength it would likely have been auto-destructive enough to not be a problem with respects to salvage by the Japanese. If it had dropped into water it would have become a small nuclear reactor and rendered itself highly radioactive (the water would have acted as a moderator, in other words).
With the Fat Man bomb, there were four simple "impact" detonators on the nose. If they had been triggered they would have ignited the high explosives in the bomb. This would not have been done with enough precision to achieve a nuclear yield, but it still would have been the detonation of some 4 tons of TNT, which would have adequately scattered the plutonium core in such a way that it would be unrecoverable.
People have asked a related questions at least a couple of times before: