Most Americans who've had a proper introduction to recent American History are aware of how JFK pretty well saved the world (much of it) back in October, 1962 at the peak of the Cuban Missile Crisis. As we know, Kennedy rejected the Joint Chiefs pressure to bomb and invade Cuba in favor of a naval blockade. Just as well, since as his former Defense Secretary Robert McNamara observed (in his documentary 'The Fog of War') Castro would have launched over 100 armed ballistic missiles had that happened.
McNamara learned of this while on a conference visit to Havana in 1992, commemorating the 30th anniversary of the crisis. McNamara had asked Fidel what he would have done had the U.S. invaded Cuba. Castro didn't hesitate, informing him that over 100 armed (with single megaton warhead) missiles would have been sent flying.
Flabbergasted, McNamara pressed him: "You really would have destroyed your country?" and Fidel replied, "Yes, and you would have too in a similar situation!"
Echoing the 'better dead than Red' meme entrenched in Americans at the time.
How close we came to nuclear war at the time was well documented in the excellent book of the tape transcripts: T'he Kennedy Tapes: Inside the White House During the Cuban Missile Crisis’, by Ernest R. May and Philip K. Zelikow (1997, President and Fellows of Harvard College).
Therein , on p. 347, for ’10:00 A.M. Oct. 24” one finds:
“At the time the quarantine became effective, the Strategic Air Command moved from the general Defense Condition 3 to Defense Condition 2, the level just below general war. In addition to ICBMs and submarine-based ballistic missiles, every available bomber – more than 1,400 aircraft- went on alert. Scores of bombers, each loaded with several nuclear weapons and carrying folders for pre-assigned targets in the Soviet Union, were kept continuously in the air around the clock with shifts- refueled by aerial tankers, taking turns hovering over Northern Canada and the Mediterranean Sea. The Soviet government was presumed to be aware of these developments.”
On p. 183 one beholds Gen. Curtis LeMay saying that "We have got to do more than take out the missiles" and he demands a massive air strike as well. Here's how that would have played out: At the first hint of U.S. attack planes picked up on Cuban radar most or all of the 100-odd Soviet IRBMs would have been launched. The targets would mainly have been U.S. east coast cities: Miami, Baltimore, Washington, DC, Philadelphia, New York, Boston, but a number of the missiles would have struck interior cities including Cleveland, Detroit, Cincinnati, Atlanta, Chicago and possibly Milwaukee.
Even as those missiles were in flight, the Kennedy White House would have been forced to go to Defcon 1, or full war condition, even as the Soviets - also now acknowledging what was happening (realizing Cuba's missile launch would make them a target), launched their own missiles. In the space of about 30 minutes, as McNamara pointed out, some 7,500 missiles would have been in the air headed for targets in the USA and USSR. Since most warheads at that time were in the 1-10 megaton range, the full nuclear exchange - lasting maybe an hour would have resulted in possibly 300 million dead and massive clouds of radiation polluting the rest of the planet via the trades and other winds.
The world escaped at least partial obliteration, thanks to Kennedy's use of reason over reaction.
Flash forward now to September 26, 1983. A Soviet satellite detects five U.S. ICBMS heading toward the USSR. This detection immediately causes alarms to sound at the Soviet Central Command in Oko with backlit screens flashing LAUNCH! Standard operating procedure at the time dictated that the command be followed with a full scale missile launch - including all 3,000 or so Soviet ICBMs - all armed with multi-megaton warheads.
But something didn't seem right to Stanislav Petrov, lieutenant colonel of the Soviet Air Defence Forces. Why only five ICBMs? Surely if the Americans had really planned a pre-emptive nuclear attack they'd have thrown their whole arsenal at the USSR.
Using his reason, like Kennedy did 20 years earlier, Petrov declared the system's indication a false alarm. Subsequent investigation showed that he was right: no missiles were approaching and the computer detection system was malfunctioning. According to the Wikipedia account:
"It was subsequently determined that the false alarm had been created by a rare alignment of sunlight on high-altitude clouds and the satellites' Molniya orbits, an error later corrected by cross-referencing a geostationary satellite."
Alignment of a satellite with sunlight on high altitude clouds nearly led to a full retaliatory response from the Russians and likely nuclear war? Yes, indeed, and the near breakdown showed a nascent weakness in the Soviet early warning system and also raised concern about the U.S. system too - also based on hair trigger alarms.
While there remains debate on the role Petrov actually played in the events that day, just as there remains debate on Kennedy's role, all generally agree that his voice of doubt- and reasoning - was enough to leverage restraint. Analogous to how Kennedy's doubt that an invasion was the answer in 1962 leveraged a restraint on precipitous action that might have led to a major nuclear exchange.
We have had then two men saving the world at different times. The question is: Will a third person come to the rescue with the next geopolitical or technical snafu? Or will our luck have run out?