Films and history books have documented the the hair's-width margin that separated the United States and the Soviet Union from nuclear conflict during 13 days in October 1962, the height of the Cuban missile crisis.
But a speech drafted by U.S. President John F. Kennedy, and newly released to the public, throws what may be the starkest light yet on just how close the sides came to starting World War III.
"My fellow Americans, with a heavy heart, and in necessary fulfillment of my oath of office, I have ordered -- and the United States Air Force has now carried out -- military operations with conventional weapons only, to remove a major nuclear weapons build-up from the soil of Cuba," Kennedy was to begin.
This speech is the highlight of an archive containing nearly 3,000 pages of notes, transcripts, and other documents kept by Robert Kennedy, the president's brother and close adviser.
It was posted online by the John F. Kennedy Presidential Library and Museum last week to coincide with the 50th anniversary of the crisis.
The newly released material offers a fascinating glimpse of the limited options open to the U.S. leader during the tense standoff between the United States and the Soviet Union.
"What this document reminds us, vividly, is that if President Kennedy had felt forced to choose what to do in the first 48 or 72 hours after the U.S. discovered the Soviet Union sneaking nuclear-tipped missiles into Cuba, he would have conducted an air strike on those missiles, as the speech tries to justify," says Graham Allison, the director of the Belfer Center for Science and International Affairs at Harvard University and an expert on the Cuban missile crisis.
"We would have the seen the chain of events that would have initiated. Down that path we would have come to nuclear war."
Kennedy's speech, of course, was never delivered. The U.S. leader instead enacted a naval blockade of Cuba and as the world held its breath, the approaching Soviet ships turned back.
But Kennedy also came close to ordering a strike after the blockade to prevent the missiles that were spotted by the United States from becoming operational.
WATCH: Kennedy announces a naval blockade of Cuba
What no one in Washington knew at the time is that Moscow already had nearly 100 smaller, fully operational nuclear weapons on the island, which would have been enough to eliminate U.S. forces and escalate the conflict into unprecedented territory.
According to Thomas Putnam, the director of the John F. Kennedy Presidential Library, the specter of war allegedly compelled the president's usual speech writer to turn down the assignment.
"One story is that Ted Sorensen, who wrote most of [Kennedy's] speeches and, I think, wrote the one where he announced to the world the discovery of the missiles, told [President Kennedy] he couldn't write that speech," Putnam says. "He didn't think we should invade and...he couldn't even come up with words that would perhaps support an invasion that would lead to a nuclear exchange. So I believe the author [of the speech] was [National Security Adviser] McGeorge Bundy."
After days of nail-biting diplomacy, Moscow pledged to withdraw its weapons and Washington pledged to stay out of Cuba.
Another notable document in the archive is a chart drawn by Robert Kennedythat divides the president's advisers and military leaders into proponents of a blockade and proponents of a strike -- men known to history as "doves" and "hawks." Arrows and question marks indicate that not all were convinced of which option was best.
Raw Material Of History
Memos detail the botched Operation Mongoose, a plan to overthrow Cuban leader Fidel Castro that helped convince Soviet leader Nikita Khrushchev to send nuclear weapons to the island.
There are also notes referring to a secret deal for the United States to withdraw missiles from Turkey as well as CIA documents describing the failed Bay of Pigs invasion and a 1964 mafia-linked plan to assassinate Castro.
"What these documents are for us is the raw material of history," says Putnam. "They allow you to see Robert Kennedy's thinking, to see the notes, the doodles, [and] what his concerns were. Since he was such a key player in the Cuban missile crisis, having these documents helps to bring history to life."
Graham Allison says one detail from the archive has particularly resonated with him.
"Bobby has his notes after a civil defense briefing in which they've heard planning for what might happen if the actions they choose end up triggering an attack, and he writes down '42 million' and '90 million.' Those, I infer, are the answer[s] to the question [of] how many Americans are estimated to die if the U.S. attacks first, as opposed to waits until the Soviet Union attacks first, in which case 90 million Americans die."
"Well, those are unbelievable numbers, if you try to think of it. There they are in his handwriting with an underline," says Allison. "Who in the world could imagine trying to make a choice about something that has such momentous consequences?"