October 27, 1962 the USS Beale had tracked and dropped signaling depth charges (the size of hand grenades) on the B-59, a Soviet Project 641 (NATO designation Foxtrot) submarine which, unknown to the US, was armed with a 15 kiloton nuclear torpedo.

Running out of air, the Soviet submarine was surrounded by American warships and desperately needed to surface. An argument broke out among three officers on the B-59, including submarine captain Valentin Savitsky, political officer Ivan Semonovich Maslennikov, and Deputy brigade commander Captain 2nd rank (US Navy Commander rank equivalent) Vasili Arkhipov.

An exhausted Savitsky became furious and ordered that the nuclear torpedo on board be made combat ready. Accounts differ about whether Commander Arkhipov convinced Savitsky not to make the attack, or whether Savitsky himself finally concluded that the only reasonable choice left open to him was to come to the surface.

During the Cuban Missile Crisis Havana conference in October 2002, US Secretary of Defense Robert McNamara stated that nuclear war had come much closer than people had thought. Thomas Blanton, director of the National Security Archive, said, "A guy called Vasili Arkhipov saved the world."

Fifty years after the crisis, Graham Allison, a American political scientist at the John F. Kennedy School of Government wrote:
“Fifty years ago, the Cuban missile crisis brought the world to the brink of nuclear disaster. During the standoff, US President John F. Kennedy thought the chance of escalation to war was "between 1 in 3 and even," and what we have learned in later decades has done nothing to lengthen those odds. We now know, for example, that in addition to nuclear-armed ballistic missiles, the Soviet Union had deployed 100 tactical nuclear weapons to Cuba, and the local Soviet commander there could have launched these weapons without additional codes or commands from Moscow. The US air strike and invasion that were scheduled for the third week of the confrontation would likely have triggered a nuclear response against American ships and troops, and perhaps even Miami. The resulting war might have led to the deaths of 100 million Americans and over 100 million Russians.”

“[i]Under no circumstances a decision to use nuclear weapons could be made or even considered in the Soviet Union (Russia) or in the United States on the basis of data from a single source or a system.” This statement is at odds with the historical facts revealed by both sides after the Cuban Missile Crisis.

Source: http://en.wikipedia.org/wiki/Cuban_Missile_Crisis