Havana ? At the height of the Cuban Missile Crisis, a Soviet submarine commander readied a nuclear attack on a United States destroyer, and another officer began assembling the weapon, according to papers released Friday.

It was only the intervention of a third officer that stopped an attack that almost certainly would have led to an annihilating retaliation by U.S. forces.

The little-known incident, detailed publicly Friday at a conference of U.S., Soviet and Cuban officials during the 1962 crisis, offered a chilling glimpse of how close the superpowers came to a nuclear exchange during the most dangerous confrontation of the Cold War.

“The sound bite here is that a guy named Arkhipov saved the world,” said Thomas Blanton, director of the National Security Archive.

The Oct. 14, 1962, discovery of Soviet missile bases on this Caribbean island 90 miles from Florida triggered a two-week standoff between the United States and the Soviet Union that brought the world to the edge of disaster.

President Kennedy ordered a naval blockade, readied forces for an attack, and demanded that Soviet Premier Nikita Krushchev withdraw the missiles. The world watched and waited as Soviet ships steamed toward the U.S. line.

On Oct. 27, U.S. destroyers came upon a Soviet B-59 submarine and began dropping signal charges to force it to surface.

Vadim Pavlovich Orlov, an intelligence officer aboard the submarine, likened the bombardment to “sitting in a metal barrel, which somebody is constantly blasting with a sledge hammer.”

Ships logs from the U.S.S. Beale and the U.S.S. Cony released on Friday confirmed the bombardment.

As the oxygen supply in the B-59 thinned and temperatures rose to 120 degrees, some sailors lost consciousness.

After a hit by a “practical depth bomb,” Orlov said, submarine commander Valentin Grigorievich Savitsky, thought a war might have begun. Unable to communicate with the Soviet general staff, he ordered the officer assigned to the nuclear-tipped torpedo to assemble it and prepare it to be fired.

But Second Captain Vasili Alexandrovich Arkhipov intervened, telling Savitsky that the conditions for firing the torpedo a rupture of the hull had not been achieved. Savitsky reversed his order and the submarine surfaced.

The missile crisis was defused the following day when Krushchev agreed to withdraw the Soviet weapons from Cuba in exchange for a public pledge by Kennedy not to invade the island and a secret promise to pull U.S. missiles out of Turkey.

Veterans from all sides of the confrontation, including Cuban President Fidel Castro, former U.S. Defense Secretary Robert McNamara and former Soviet KGB agent Nikolai Leonov, gathered Friday in Havana to open a two-day conference and release several declassified documents.

Conference organizers said understanding the crisis could help future leaders avoid nuclear war.