For reference, there have been a number (dozens, at least) of nuclear devices dropped accidentally all over the world (some of which landed in the USA), but non

For reference, there have been a number (dozens, at least) of nuclear devices dropped accidentally all over the world (some of which landed in the USA), but none have ever accidentally detonated. This was a plot device in the popular Fallout games. Where a city had built up around a nuclear bomb which failed to detonate during a nuclear war.