Three days after John F. Kennedy was sworn in as president, a nuclear bomb that could have devastated much of the U.S. East Coast nearly exploded when the B-52 bomber carrying it broke up over North Carolina, according to a declassified internal report published Friday.

Three of the eight crew members died and the bomber's two Mark 39 hydrogen bombs — each of them four megatons, 250 times more powerful than the device that destroyed Hiroshima, Japan, in 1945 — separated as the B-52G crashed in Faro, N.C., near Goldsboro, on Jan. 24, 1961.

The weapons didn't explode when they hit the ground in an incident that was widely reported at the time.

What wasn't reported was that while one bomb plowed into the ground and disintegrated, the second nuke fired three of its four arming mechanisms and deployed the parachute designed to slow its descent to optimum blast altitude, according to the document, which was obtained under the Freedom of Information Act by author Eric Schlosser and was first published Friday by The Guardian.

The 1969 document — in which Parker Jones, a nuclear weapons safety specialist at Sandia National Laboratories in Albuquerque, N.M., analyzes a book about the B-52 crash — chillingly observes that "one simple, dynamo-technology low voltage switch stood between the United States and a major catastrophe."

"The Mk 39 Mod 2 bomb did not possess adequate safety for the airborne alert role in the B-52," Jones wrote. "... If a short in the 'arm' line occurred in a mid-air breakup, a postulate that seems credible, the Mk 39 Mod 2 bomb could have given a nuclear blast."

Jones dryly notes: "It would have been bad news — in spades."

Although the precise details of the incident weren't disclosed, the peril was highlighted in the 2011 book "The Goldsboro Broken Arrow," by former Air Force officer Joel Dobson, which quoted the commander of the explosive ordnance disposal team for the crash as saying: "How close was it to exploding? My opinion is damn close. You might now have a very large Bay of North Carolina if that thing had gone off."

The commander was quoted as having said the bomb carried a destructive yield greater than all of the combined munitions ever detonated in the history of the world to that point — including the nuclear bombs that hit Hiroshima and Nagasaki, Japan.

In 2011, Jun Takada, a professor at Sapporo Medical University and director of the Japanese Radiation Protection Information Center, calculated that a four-megaton nuclear test carried out by China in 1975 killed 190,000 people by spreading radiation poisoning over almost 115,000 square miles — in a radius that would extend from Goldsboro almost to New York City.

Schlosser obtained the document while researching a new book on the nuclear arms race, "Command and Control."

"The U.S. government has consistently tried to withhold information from the American people in order to prevent questions being asked about our nuclear weapons policy," Schlosser told The Guardian. "We were told there was no possibility of these weapons accidentally detonating, yet here's one that very nearly did."

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