We have had a crap ton of Broken Arrow incidents over the years. Most recovered, some not. Tybee Island is one of the never recovered, as is the A-4 that rolled off a carrier deck.

My favorite is the B-36 landing in Albuquerque in the 1950s. The weapon was so heavy, procedure was to salvo the weapon to save the aircraft, if there was an emergency on landing, leading to a go around. This required removal of a safety pin on final approach. The crew chief pulled the pin, and the weapon dropped through the closed bomb bay doors.

Oops.

Not 100% sure, but that weapon may have been the type that the core was carried separately, and only inserted when you wanted it to go nuclear.

Quote:

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The bomb which landed intact had 4 safety systems to prevent accidental nuclear detonation. Of those four, three failed and the weapon had nearly completed its arming sequence. Of the four, only one switch had kept the weapon from going to fully armed and likely a nuclear detonation.

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The National Nuclear Museum in ABQ, mentioned above, is a fantastic place for anyone interested in nuclear weapons. Besides the Palamores casing mentioned above, they have a great display of the evolution of arming switches, and PALs, Permissive Action Links, which arm the bombs.