The centrifugal forces set off a trigger in the cockpit which would be used to drop the payload in the back of the plane.
Only one of six switches stopped the first warhead from detonating. (US Air Force)
That payload was two hydrogen bombs, which dropped out of the plane as it broke up in the sky.
Five of the eight crew were able to bail out safely, but three were killed.
Meanwhile, the two hydrogen bombs fell to the ground.
By pure luck, neither of the weapons exploded.
The first weapon had landed in a field on a farm, landing reasonably softly because of its deployed parachute.
With one of the 24-megaton warheads, there were six interlocking safety mechanisms which needed to be triggered for the bomb to explode.
“When Air Force experts rushed to the North Carolina farm to examine the weapon after the accident, they found that five of the six interlocks had been set off by the fall,” nuclear safety supervisor Parker F. Jones wrote in a 1969 report.
“Only a single switch prevented the 24-megaton bomb from detonating and spreading fire and destruction over a wide area.”
The second bomb went deep into a muddy field, requiring a complex operation to retrieve it. (US Air Force)
The second bomb landed in a muddy field, leaving a 1.5m hole in the ground.
When it was recovered after a three-day operation, they found the safety switch had been turned to “Armed”.
It created a mystery as to why this bomb did not detonate.
The conclusion from investigators was that the impact from hitting the earth shifted the switch to “Armed”, but that same impact had broken the circuits that would have set the bomb off.
After breaking up on impact and sinking into deep mud, some major components of the bomb have still not been recovered.
If either bomb had detonated, it would have likely wiped out a city of about 30,000 people.
The farmer was paid $100 by the US government for a 61m-radius section of the farm.Â
They are still allowed to use the land for agricultural purposes but forbidden from digging more than five feet down.
Major components of the second warhead remain buried deep in a field in North Carolina. (Google Maps)