Thunderball

Declassified documents from 1968 reveal that a US B52 crashed on the ice off Greenland complete with four nuclear weapons. Only three were ever recovered. Story Here

The high explosives surrounding the four nuclear weapons had detonated but without setting off the actual nuclear devices, which had not been armed by the crew.

....

The documents make clear that within weeks of the incident,
investigators piecing together the fragments realised that only three of the weapons could be accounted for.

Ian Fleming's Thunderballimmediately comes to mind. SPECTRE stage a crash of a British nuclear bomber off the coast of the Bahamas. They then dive and recover the nukes. It's my favorite Bond novel and a so-so film. However, there was one part of the novel that gave me a chill. (This story proves that there was something to it.)

Bond is accessing the situation with M:

'Would that [the crash landing] explode the bombs?'

'No they are absolutely safe until they're armed. Apparantly even a direct drop, like the one from the B-47 over North Carolina in 1958, would only explode the TNT trigger to the thing. Not the plutonium.'

Yikes.