On the evening of September the 26th, 1983, the actions, or possibly inactions, of a lieutenant colonel in the Soviet Air Defense Forces would change the course of history.
The man in question was Stanislav Petrov, who was on duty in the Soviet's nuclear early warning command centre.
Code-named 'Oko', meaning eye, it collated information from multiple satellites in geosynchronous orbits that endlessly monitored the skies for ballistic missiles carrying nuclear warheads on their way to attack the Soviet Union.
It would prove to be a fateful duty for Stanislav because shortly after midnight the computers in the station detected an American missile heading towards the Soviets.
It was and still is the policy of Russia to launch a second-strike attack, meaning that if Stanislav had reported the incident to his superiors they would have almost certainly retaliated with their own nuclear strike.
Stanislav had a decision to make. Should he alert his superiors or dismiss the attack as a false alarm?
In an act of incomparable bravery, he dismissed the missile and the subsequent four missiles that were to follow as malfunctions of the missile detection system.
He was right.
Years later the 'man who saved the world', when asked about what he did that night, simply said he 'did nothing'.
But if it had been another officer on duty would they have made that decision?
How many other near misses have happened that we don't know about? Could our protection from nuclear obliteration really be this fragile?
Listen to the fifth episode of 'Weapons That Changed The World' in full below...
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The United States was the first country to develop nuclear weapons. Russia followed soon after.
Between them, the two superpowers hold the vast majority of the world's nuclear weapons.
The paranoia of the Cold War, it would seem, may not be a thing of the past. But less powerful countries have also long had ambitions to hold nuclear weapons.
Much of the world fears Iran or North Korea developing them and the capability to deliver them.
The story of nuclear warfare arguably starts in 1789 with the discovery of the chemical element uranium.
But it wasn't until nearly 150 years later that nuclear fission was first achieved.
This is where the nucleus of an atom is split into smaller nuclei, producing a huge amount of energy - a concept which underpins all nuclear weapons.
Nuclear fusion, on the other hand, is where two or more nuclei fuse together.
This produces an enormous amount of binding energy - it's the process of fusion that that powers active stars.
These immensely powerful processes provide the science behind the technology of nuclear weapons.
Atom bombs - like those dropped on Hiroshima and Nagasaki - use conventional explosives to ignite nuclear fuel through the power of nuclear fission alone.
The Manhattan Project, led by the United States and supported by Canada and the UK, produced the first atomic bombs.
Physicist Robert Oppenheimer was the director of the Los Alamos Laboratory that designed the bombs.
On July 16, 1945, the US tested the first nuclear weapon, 'Trinity', in New Mexico. Around 425 people witnessed Trinity exploding with the power of around 20,000 tonnes of TNT.
Some civilians noticed the huge explosion and were fed a cover story about:
"A remotely-located ammunition magazine containing a considerable amount of high explosives and pyrotechnics exploding."
As the bomb exploded Oppenheimer would later describe how those around him reacted:
The world would never be the same again.
The uranium bomb dropped on Hiroshima killed more than 140,000 people within months.
Many more would later die from radiation-related illnesses. The heat explosion burnt the shadows of the dead into the pavements of the city.
A conservative estimate of deaths from the second bombing at Nagasaki is around 75,000.
Whether it was right to drop the bombs on Japan has been fiercely debated by historians and ethicists ever since.
Were the immediate and horrific deaths caused by the bombs outweighed by lives potentially saved in the long run by the quick end of the war?
Some historians say yes, while others have argued that Japan would have surrendered soon even without the use of the bombs.
The Japanese atrocities in the Second World War, including the widespread use of torture and testing of chemical weapons on prisoners, were horrendous but did they justify the use of atomic weapons?
Far more powerful weapons were just around the corner though. Soon afterwards more-advanced 'boosted', or 'layered' atomic bombs began being developed.
These used thermonuclear fuel around or inside the atomic core to greatly increase the power of the weapon.
Powered by a nuclear fission reaction triggering a nuclear fusion reaction, they were much more deadly.
The hydrogen bomb, developed soon afterwards, would use lots of hydrogen fuel that a nearby atomic core would ignite.
The United States tested a hydrogen bomb at Bikini Atoll in 1954 (below) that was more than 1,000 times more powerful than the atomic bomb dropped on Hiroshima less than 10 years earlier.
If a Hydrogen bomb were to be dropped on South Korea an estimated 2 million residents of Seoul would be instantly killed.
Nuclear warfare would fill the heart of the world with fear and regret and would define the decade and the Cold War to follow.
A single individual with great power could now decide to take away the lives of millions in a matter of hours. Should one person have this much power?
In 1981, Harvard law professor Roger Fisher proposed a thought experiment.
What if the launch codes to a nuclear weapon were surgically implanted inside the chest of a volunteer?
If the president wanted to use nuclear weapons they'd first have to ruthlessly hack out the codes from the stomach of the volunteer before they could launch.
If they could kill one innocent person with their own two hands, then they'd truly have better insight into understanding the gravity of killing millions more innocent people in a faraway land.
There has, however, been a consistent and underlying rationality to the production of nuclear weapons.
Developed extensively around the time of the fast growth of nuclear weapons, Game Theory underpins the cold logic behind storing stockpiles of deadly world-destroying weapons.
Mutually assured destruction (MAD) holds that if two rational parties hold nuclear weapons neither will ever rationally use them.
If both parties have the power to cause unseen damage to the other, no one would ever rationally strike first as they would, in doing so, condemn their own country to the inevitable retaliation strike.
Thus a nuclear stalemate is born, with both sides willing and ready to bite back, but never make the first move.
This Cold War logic is widely accepted and nations who could quickly stockpiled thousands of nuclear weapons to defend against the other powers doing the same.
Yet critics of the idea point to potential pitfalls in this logic. MAD assumes either party hasn't developed the technology to neutralise an incoming strike.
If the threat of a nuclear attack is no more then you gain the power to launch without consequence.
The logic also fails if those who hold nuclear weapons are no longer rational.
Nuclear terrorism poses a security threat to the world like never before, while fears exist that if a group like the so-called Islamic State or other organisations with a death wish were to ever gain hold of nuclear weapons, there'd be little stopping them from launching.
Finally, returning to Stanislav Petrov, one detection error could provide a rational side with catastrophically-incorrect information.
If America truly had launched weapons in 1983, it would have been rational for Russia to retaliate.
It would also have been entirely rational for America to retaliate back. The incident that evening in Russia is by no means isolated.
The total number of nuclear weapons in the world peaked in 1986 at more than 60,000.
Dedicated international efforts to reduce this have been successful.
In 2018 around nine countries own approximately 15,000 nuclear weapons, although it is worth remembering that the destructive power of each nuclear warhead has increased significantly as technology has advanced.
Regardless, when we as societies subscribe to holding nuclear weapons, it is important to understand what we are committing to.
In the Hiroshima Peace Memorial Museum, a sign in the lobby states that if humans are to tolerate nuclear weapons and the logic behind them then they must be committed to accepting them, and the even more destructive weapons that will be developed in the future, as existing alongside humans for the rest of history.
Japan since WWII has held a strong policy of non-weaponisation of nuclear technology.
As the only country in the world ever to experience a nuclear attack, the country's statement that human beings and nuclear weapons cannot exist indefinitely is indeed a profound one.
However, it is up to the governments and ultimately the people who choose those governments to decide whether they want to live alongside these catastrophically-powerful weapons.