In 1961, Goldsboro, North Carolina, and, really, a huge chunk of the East Coast, was almost wiped out when an American B-52 bomber had a mid-air accident and started to break up, dropping two massive nuclear bombs above the city in the process. One of the bombs dropped with all of its safeties secure, but one of them didn’t. The Guardian:

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“ne of the devices behaved precisely as a nuclear weapon was designed to behave in warfare: its parachute opened, its trigger mechanisms engaged, and only one low-voltage switch prevented untold carnage.”

The bombs were huge, says the Guardian, basing their report on a 1969 document that was obtained through a freedom of information request by journalist Eric Schlosser, who was working on book about America’s close calls with its nuclear arsenal. At four megatons, the bombs each harnessed more than 250 times the destructive potential of the bomb dropped on Hiroshima, Japan.

Slate:

The accident is not news, but just how close the military came to wiping out a swath of the Eastern Seaboard has long been debated. For years the military insisted that the hydrogen bombs were never in danger of detonating. The secret document, written by a nuclear weapons safety supervisor in 1969 …makes it clearer than ever that was not the case.

More from Smithsonian.com:

The U.S. Once Wanted To Use Nuclear Bombs as a Construction Tool