It was March 11, 1958, an Air Force B-47 Stratojet carrying Atomic and Hydrogen bombs beheld by the United States of America was making it's way from Savannah, Georgia to the United Kingdom. This Sratojet was sent on a mission to help out in operation Snow Flurry, however it did not made it's destination.
On it's way to the operation, the flight was cruising over ''South Carolina''. The pilots then noticed a fault light in the cockpit displaying signs of trouble with the locking pin of one the bombs in the cargo bay. Atomic and Hydrogen bombs were always carried in the planes just in case a war broke out with the Soviet Union (Russia). The nuclear bomb in the question was a 26 Kilo Mark 6 which is even more powerful than the Fat Man bomb which was dropped on Nagasaki.
When the Air Force Captain, Bruce Kulka was told about the issue in the cargo bay, he immediately rushed to the bomb and inorder to steady himself in a moving war plane he reached out around the bomb and ended up pulling the emergency release pin. The bomb the pushed it's way open through the bay doors and fell from 15,000 feet high on rural South Carolina.
Thank heavens, the bombs fission core was not attached to the bomb as it was stored in an other part of the plane separately. The bomb was not technically armed. But, it was still loaded with 7,600 pounds of traditional explosives enough to kill hundreds. The bomb fell in a forest land which flattened a good section of the forest, leveled some houses and resulted in creation of a mushroom cloud which can be seen from miles. The impact left a crater about 70 feet wide and 35 feet deep which now has become a tourist attraction.
Miraculously, there were no casualties and only 6 people were injured by the explosion of the bomb's conventional explosive load. The victims later sued the United States Air Force (USAF) with US$54,000 equivalent to $478,526 now.