The incident happened when two Mark 39 hydrogen bombs were accidentally dropped over Goldsboro, N.C., when a B-52 bomber broke up in midair. And it was because one "highly vulnerable" switch did not activate that nuclear disaster was averted.
The Guardian newspaper said the document, obtained under the Freedom of Information Act, gives the first conclusive evidence that the United States came breathlessly close to disaster in the January 1961 incident.
The document said one of the two bombs behaved exactly in the manner of a nuclear weapon in wartime, with its parachute opening and its trigger mechanisms engaged. Only one low-voltage switch prevented cataclysm. If the bomb had activated, the resulting explosion would have been 260 times more powerful than the bomb that devastated Hiroshima.
Fallout could have spread over Washington, Baltimore, Philadelphia and even New York City, the paper said, threatening the lives of millions of people.
In the document, Parker Jones, a senior engineer in the Sandia National Laboratories responsible for the mechanical safety of nuclear weapons, concluded that "one simple, dynamo-technology, low-voltage switch stood between the United States and a major catastrophe."
The bomb landed on a field near Faro, North Carolina, and the other in a meadow. Researchers say that three of four safety mechanisms designed to prevent unintended detonation failed to operate properly in the Faro bomb. When the bomb hit the ground, a firing signal was sent to the nuclear core of the device and it was only the final, highly vulnerable switch that averted a disaster.
