Since the beginning of the U.S. nuclear program, there have been 33 nuclear weapons accidents, known as "broken arrows," according to Eric Schlosser in his book: Command and Control. A "broken arrow" is the Pentagon's phrase for an unexpected event involving nuclear weapons that result in the accidental launching, firing, detonating, theft, or loss of the weapon.
An example of a "broken arrow" is the Goldsboro accident in which a B-52 carrying two nuclear bombs broke apart, dropping the bombs over Goldsboro, North Carolina. Or the time in 1966 when a B-52 crashed into a KC-135 Stratotanker during a refueling operation, releasing four thermonuclear bombs over Spain. It's hard to believe, but there are 31 more times these doomsday scenarios played out.
Here is a brief, terrifying history of some of America's nuclear mishaps: