Fifty years ago, the world teetered on the brink of nuclear Armageddon. On October 16, l962, President John F. Kennedy learned from US aerial surveillance that the Soviet Union was installing offensive nuclear missile sites in Cuba, 90 miles from the coast of Florida. He was stunned. The president broke the news to the public on October 22. "This sudden, clandestine decision to station strategic weapons for the first time outside of soviet soil is a deliberately provocative and unjustified change in the status quo, which cannot be accepted by this country," he said. President Kennedy announced the imposition a naval blockade around Cuba. He also gave Soviet premier Nikita Khrushchev an ultimatum. "I call upon Chairman Khrushchev to halt and eliminate this clandestine reckless and provocative threat to world peace." In other words, remove those missiles in Cuba. Or else. So why did Nikita Khrushchev risk World War III by putting nuclear missiles in Cuba? After all, a year before, he'd promised President Kennedy he would do no such thing. "That's the question that everybody is trying to solve," said Svetlana Savranskaya, director of Russia programs at the National Security Archive, and the editor of a new book, The Soviet Cuban Missile Crisis. "There's stunningly little thinking on the Soviet side about what happens if the United States responds in an aggressive way." Perhaps because the United States had deployed nuclear missiles in Turkey. "Right along the Soviet borders," Savranskaya said, "and that was a constant source of humiliation." So Khrushchev figured he had every right to do the same thing. "Khrushchev felt that this is giving the Americans a dose of their own medicine," according to James Hershberg, a professor of History and International Affairs at George Washington University. "At one point Kennedy reacted to what Khrushchev did, saying 'it's as if we started to deploy missiles in Turkey, that would be goddamned dangerous!' And his adviser McGeorge Bundy said, 'well we did, Mr. President'." Nikita Khrushchev's son, Sergei Khrushchev, is a historian at the Watson Institute for International Studies at Brown University. "[Khrushchev] did not understand at the time that the American mentality is different. Europeans, Soviets, all their history, had enemies at the gate," Sergei said. Russians were used to being threatened. Sergei Khrushchev says that as leader of the world's other Superpower, his father also felt an obligation to protect his allies. "When Castro, after the Bay of Pigs, declared officially that he joined the Soviet bloc, he put this obligation on my father's shoulders. So Khrushchev decided to send missiles there as a diplomatic signal: Don't invade Cuba. We are serious." Svetlana Savranskaya says in the spring and summer of l962, the Soviets were receiving lots of intelligence that the United States was preparing another invasion. "Khrushchev doesn't want to lose Cuba. It's his most important ally, the ally that's genuine. Plus, it's Latin America. The Soviets don't have real allies in Latin America," she said. "Cuba is so important for the Soviets." The Cubans weren't just a valuable Cold War ally. They were genuine folk heroes in the Soviet Union. "The Soviets were in love with the Cuban Revolution," Savranskaya said. "It was really a love affair. They looked at Cuba and saw their own revolutionary youth. " "All the Soviets, from the top to the bottom, wanted to help the Cubans fight against possible American invasion, American aggression," said Sergei Khrushchev. Unfortunately, Khrushchev nearly did provoke a full-scale US invasion, by sending missiles to Cuba. And here's where the story gets really scary. Cuba was far more armed and dangerous than the US realized. Svetlana Savranskaya says there were 42,000 Soviet combat troops in Cuba. The US didn't know about them. The Soviets also had about 180 nuclear warheads in Cuba, Savranskaya says, and the United States thought they had zero. "What we know now is that without doubt, if there was an invasion of Cuba by US land forces, there would be a nuclear response, and then the US would have to respond with nuclear weapons." The crisis reached a boiling point on October 27th, says James Hershberg. "Clearly, October 27, l962 goes down as the most dangerous day in human history." Savranskaya added that "it's dangerous, amazingly not because of decisions the leaders are taking, but because the situation is spiraling out of control." A Soviet commander in Cuba, acting without authorization from Moscow, shot down a U-2 spy plane over Cuba, killing the American pilot. Another American U-2 accidentally strayed into Soviet territory in Far East for a couple of hours. "Also, by October 27, we've learned, you had Soviet submarines around the blockade equipped with nuclear torpedoes," Hershberg said. "In at least one case, and the evidence is still coming in on this, arguments breaking out as to whether World War III has broken out and they should use their nuclear torpedo or get sunk." The next day, Soviet leader Nikita Khrushchev went on Radio Moscow, with an announcement. "Premier Khrushchev has sent a message to President Kennedy today. The Soviet government has ordered the dismantling of weapons in Cuba, as well as their crating and return to the Soviet Union." In return, President Kennedy promised not to invade Cuba, although he refused to put it into writing. He also agreed to withdraw the US nuclear missiles in Turkey. "It was a compromise on both sides; admittedly the Soviets had to undo their major deployment. But to see it as one side giving up isn't correct." Both sides blinked. Americans thought the crisis was over. President Kennedy made it official by lifting the blockade on Cuba on November 20th, after receiving assurances from Khrushchev that he'd withdrawn all of his offensive weapons. In fact, he hadn't. "What we've only learned in the last 10 years or so was that the tactical nuclear weapons were still there," said historian James Hershberg. Svetlana Savranskaya says Khrushchev decided to leave these weapons in Cuba. "For some time in November, which we call the November Crisis, the Soviet position was that they would train the Cubans to use the remaining nuclear weapons, and transfer tactical nuclear weapons to the Cubans, which would have been the most dangerous situation." In other words, Cuba almost became a nuclear power. "Had Kennedy discovered that, after this incredible crisis, this incredible rupture in trust, that Khrushchev was lying again, the pressure to invade, to get rid of the threat permanently, would have been overwhelming," according to Hershberg. Khrushchev changed his mind, and secretly withdrew the remaining weapons in December, over the vigorous objections of Fidel Castro. There are lots of lessons from the Cuban Missile Crisis. But here's what President Kennedy's Defense Secretary, Robert McNamara, told filmmaker Errol Morris in his award winning documentary, The Fog of War. "At the end we lucked out. It was luck that prevented nuclear war." McNamara said. "We came that close to nuclear war at the end. Rational individuals. Kennedy was rational. Khrushchev was rational. Castro was rational. Rational individuals came that close to total destruction of their societies. And that danger exists today." McNamara added that the major lesson of the Cuban missile crisis was "the indefinite combination of human fallibility and nuclear weapons will destroy nations." But, at least 50 years ago, it didn't.