In February of 1958 an F-86 fighter plane flying near Savannah Georgia collided with a B-47 bomber carrying a nuclear bomb.
The crew of the bomber received permission to release the bomb to prevent an explosion during an emergency landing. The bomb was dropped in to the ocean just off of Savannah Georgia, where it remains to this day.
There seems to be some confusion about whether the bomb was capable of a nuclear detonation. No unusual amounts of radiation have been detected in the area.
Video From HistoryPod
Video From Deep South Divers