
On January 23rd, 1961, the United States almost nuked itself by accident. On that day, according to a recently unclassified document obtained by The Guardian, the US Air Force mistakenly dropped a pair of hydrogen bombs over Goldsboro, North Carolina. The bombs each carried a 4-megaton payload and were about 260 times more powerful than the atom bombs dropped on Hiroshima and Nagasaki, Japan, in 1945 during World War II, The Guardian says in a report.
http://www.theverge.com/2013/9/21/4755600/us-atomic-bomb-north-carolina-accident-1961
That is quite shocking although with the amount of arms around at the time, shouldn't be surprising so many accidents could happen.