The US Air Force nearly detonated an atomic bomb over North Carolina that could have killed millions of people in the country, a secret document has revealed.On January 23,1961, the US Air Force accidentally dropped two Mark 39 hydrogen bombs over Goldsboro, North Carolina. The bombs fell to earth after they became separated from a B - 52 bomber, which went into a tailspin in mid - air,The Guardianreported based on a secret document obtained by investigative journalist Eric Schlosser under the Freedom of Information Act. One of the bombs, which was designed to be used in warfare, acted exactly as a nuclear weapon when its parachute opened and its trigger mechanisms engaged. However, one low-voltage switch, which failed to flip, prevented millions of Americans from being killed. Each bomb carried a payload of 4 megatons, equal to 4 million tons of TNT explosive. Had the bomb exploded, it would have been 260 times stronger than the bomb the US dropped on Hiroshima in Japan in 1945 and millions of people in Washington, D.C., Baltimore, Philadelphia, New York City, and the areas in between could have been killed. "One simple, dynamo-technology, low-voltage switch stood between the United States and a major catastrophe," Parker Jones, who is a senior engineer in the Sandia National Laboratories responsible for the mechanical safety of nuclear weapons, said in the document. "The MK 39 Mod 2 bomb did not possess adequate safety for the airborne alert role in the B-52," Jones noted. Jones, whose report was written 8 years after the incident, said that three of the four mechanisms designed to prevent unintended detonation failed to operate. When the bomb struck the ground, a firing signal was sent to the nuclear core of the device and it was only the final, highly vulnerable switch that saved the lives of millions of Americans. Since the incident took place, there has been persistent speculation on how serious it had been but the US government has repeatedly dismissed the fact that its nuclear arsenal threatens the lives of Americans. The US is currently planning to test nuclear missiles next week on the same day that heads of states and foreign ministers from around the world are to hold a high-level meeting on nuclear disarmament at the United Nations headquarters in New York. Two test launches have been scheduled for the country’s nuclear-capable Intercontinental Ballistic Missiles (ICBMs) on September 22 and September 26.