The most dangerous day of all was apparently October 27, 1962 - when a US Navy destroyer dropping depth charges off the Cuban coast almost accidentally hit the hull of a Soviet submarine carrying a nuclear warhead.
The U.S. military "did not have a clue that the submarine had a nuclear weapon on board," said Thomas Blanton, director of the National Security Archives.
The nonprofit archive at George Washington University collected many of the documents for study during the three-day conference back in 2002.
The depth charges "exploded right next to the hull," Vadim Orlov, the submarine's signals intelligence officer, said in a written account of the incident. "It felt like you were sitting in a metal barrel, which somebody is constantly blasting with a sledgehammer."
At first, submarine crew members considered using the nuclear weapon, thinking war had erupted. But they ultimately surfaced, showing themselves to their American pursuers and defusing the tension.