Read the whole thing. Excerpts:
A secret document, published in declassified form for the first time by the Guardian today, reveals that the US Air Force came dramatically close to detonating an atom bomb over North Carolina that would have been 260 times more powerful than the device that devastated Hiroshima.
The accident happened when a B-52 bomber got into trouble, having embarked from Seymour Johnson Air Force base in Goldsboro for a routine flight along the East Coast. As it went into a tailspin, the hydrogen bombs it was carrying became separated. One fell into a field near Faro, North Carolina, its parachute draped in the branches of a tree; the other plummeted into a meadow off Big Daddy's Road.
Jones found that of the four safety mechanisms in the Faro bomb, designed to prevent unintended detonation, three failed to operate properly. When the bomb hit the ground, a firing signal was sent to the nuclear core of the device, and it was only that final, highly vulnerable switch that averted calamity.