Goldsboro Incident

In 1961, a B-52 bomber went into a tailspin and broke up mid-air, accidentally dropping two Mark-39 hydrogen bombs over Goldsboro, North Carolina. One of the bombs worked exactly as intended. Its parachute deployed and it's triggers activated, armed and ready to detonate on impact. 3 of the 4 safety switches failed and a single low-voltage switch prevented two 4 megaton nuclear explosions. A part of one of the bomb is still buried in concrete in a fenced off area in Goldsboro.