A US atom bomb nearly exploded in 1961 over North Carolina that would have been 260 times more powerful than the device that devastated Hiroshima, according to a declassified document published in a British newspaper on Friday.

The Guardian newspaper said the document, obtained by investigative journalist Eric Schlosser under the Freedom of Information Act, gave the first conclusive evidence that the United States came close to a disaster in January 1961.

The incident happened when two Mark 39 hydrogen bombs were accidentally dropped over Goldsboro, North Carolina, after a B-52 bomber broke up in midair.

There has been persistent speculation about how serious the incident was and the US government has repeatedly denied its nuclear arsenal put Americans’ lives at risk through safety flaws, the newspaper said.

But the newly published 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 a cataclysm.

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.”

Jones’ report, titled “Goldsboro Revisited or: How I Learned to Mistrust the H-Bomb,” was written eight years after the accident in which one hydrogen bomb fell into a field near Faro, North Carolina, and the other into a meadow.

He found 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.

“The MK 39 Mod 2 bomb did not possess adequate safety for the airborne alert role in the B-52,” Jones concluded.

The Guardian said the document was found by Schlosser as he was researching a new book on the nuclear arms race, ‘Command and Control’.

The US government has acknowledged the accident before, but the 1969 document is the first confirmation of how close the United States came to nuclear catastrophe on that day.

“It would have been bad news in spades,” wrote its author, US government scientist Parker F Jones.

The accident happened at the height of the Cold War between the United States and the Soviet Union.

“The US government has consistently tried to withhold information from the American people in order to prevent questions being asked about our nuclear weapons policy,” said Schlosser.

“We were told there was no possibility of these weapons accidentally detonating, yet here’s one that very nearly did.”

The world’s first nuclear weapons explosion on July 16, 1945 in NewMexico, when the United States tested its first nuclear bomb. Not three weeks later, the world changed.On August 6, 1945, the United States dropped an atomic bomb on the Japanese city of Hiroshima. It killed or wounded nearly 130,000 people.

Three days later, the United States bombed Nagasaki. Of the 286,00 people living there at the time of the blast, 74,000 were killed and another 75,000 sustained severe injuries. Japan agreed to an unconditional surrender on August14, 1945; it also resulted in the end of World War II.

In 1958, nearly 10,000 scientists presented to United Nations Secretary-General Dag Hammarskjold a petition that begged, “We deem it imperative that immediate action be taken to effect an internationalagreement to stop testing of all nuclear weapons.”France exploded its first nuclear device in 1960 and China entered the “nuclear arms club” in October 1964 when it conducted its first test.

The United States, Soviet Union and some sixty other countries signed atreaty to seek the ends of the nuclear arms race and promotedisarmament on July 1, 1968. The treaty bars nuclear weapons statesfrom propogating weapons to other states and prohibits states without nuclear weapons to develop or acquire nuclear arsenal. It permits theuse of nuclear energy for peaceful purposes. It entered into force in 1970 and was extended indefinitely and unconditionally on May 11, 1995.In 1974, India conducted its first nuclear test: a subterranean explosion of a nuclear device (not weapon). India declared it to be a”peaceful” test, but it announced to the world that India had the scientific know-how to build a bomb. At this time, the five declared nuclear weapons states are the USA, USSR, UK, France and China.

In December, 1986, The South Pacific Nuclear-Weapon-Free Zone was put into effect. American and North Korean delegations met in Geneva in autumn 1994 to establish a framework to resolve nuclear issues in the Korean peninsula. Under the agreement, North Korea would sign a treaty on the non-proliferation of nuclear weapons in exchange for U.S. support in building safe nuclear energy facilities and formal assurance against the threat or use of nuclear weapons by the U.S. against North Korea. Both sides agreed to take steps towards better political and economic relations. In subsequent years, South Korea and Japan have invested billions to help build safe nuclear energy plants in North Korea. By 2003, North Korea has cancelled this and all other international agreements on non-proliferation.

The United Nations, on December 12, 1995, decreed an immediate ban on all nuclear testing and urged disarmament with the vision of a world free of nuclear weapons. Later that month, ten Southeast Asian countries signed the Bankok Treaty, establishing the Southeast Asia Nuclear-Weapon-Free Zone. In Spring 1996, 43 African nations sign the Pelindaba Treaty establishing the African Nuclear-Weapon-Free Zone.

On September 10, 1996, the United Nations, in a landslide vote, adopted the Comprehensive Test Ban Treaty and two weeks later, the United States was the first to sign. (The US Senate, however, rejected thetreaty three years later.)

On May 11, 1998, India shocked the world by exploding three nuclear devices amounting to about six times the destructive power of the American bomb dropped on Hiroshima in 1945. The next day, it tested two more nuclear explosions. The world was stunned when Pakistan responded with six nuclear arsenal tests of its own.

World leaders admonished the two long-time adversaries in breaking the Comprehensive Test Ban Treaty (put into force in 1970). The US imposed strict economic sanctions against both countries and lobbied for the World Bank, International Monetary Fund, and other countries to

do the same. The sanctions were lifted in 2001 when the US needed Pakistan and India’s support to fight al Qaeda and other terrorist cells in Afghanistan.