Tensions were heightened between the USSR and the US in the aftermath of the downing of flight 007 in September 1983.

A Korean Air Lines passenger jet flying from New York had strayed into Russian airspace.

After supposedly failing to identify itself, Soviet fighter jets shot down the plane and killed 269 civilians.

US President Ronald Reagan condemned the action as 'barbaric' and 'a crime against humanity that must never be forgotten.'

President Reagan had already annoyed the Soviets with his proposals for a missile defence system known as the Strategic Defence Initiative or 'Star Wars.'

"When President Reagan started this program, Soviet intelligence had already obtained information on the Star Wars program, and they were scared," said Oleg Kalugin, a former KGB general.

"They were convinced they would never be able to match the US program for purely financial reasons."

Tensions were further heightened in the aftermath of the 007 incident when the US banned the Russians from their airspace.

Soviet leader Yuri Andropov had been convinced for years that a nuclear attack by the US was imminent, a belief that was bolstered by Reagan's sabre rattling.

While he was head of the KGB, Andropov put his agents on high alert and warned them to expect action by the US -- in 1981, he had initiated covert operations in an attempt to determine America's intentions.

"We had some clandestine reports that suggested great alarm in Moscow," said Melvin Goodman, formerly a senior CIA analyst.

"But frankly they weren't taken very seriously by anyone but the analysts."

It was in this dangerous climate that lieutenant-colonel Stanislav Petrov worked.

On September 26th, he was the officer on duty at the Serpukhov-15 bunker near Moscow.

The facility was designated as an early warning station that would be used to launch nuclear attacks against Russia's enemies.

Just after midnight, Petrov received the computer report that would bring the world to the brink of destruction.

According to the recently installed monitoring system, a missile had been launched at the USSR from American airspace.

Russian military protocol dictated that Petrov should launch an all-out nuclear strike first, and only then inform his superiors who would then commit additional forces to the conflict.

Petrov's first instinct was that this was a computer error -- and he was doubtful that America would start World War III with a single missle.

"I had a funny feeling in my gut," said Petrov.

"I didn't want to make a mistake. I made a decision, and that was it."

Seconds later, another missile appeared. Then another. In all, five missiles were being tracked.

As the personnel in the bunker became agitated at the prospect of imminent nuclear war, Petrov kept a cool head -- surmising that five missiles still constituted a poor first strike.

He went with his instincts, knowing that the first missiles would be striking Moscow within minutes -- resolving his doubts definitively.

The minutes crawled by slowly until the realisation dawned on Petrov and his colleagues that this was indeed a glitch created by their early warning system.

Petrov's actions had averted an unnecessary nuclear conflict -- but his actions were far from appreciated by his superiors.

He had violated military protocols -- and the young and promising officer would pay with his career.

After a hostile investigation, Petrov was reassigned to a less sensitive role and ultimately took retirement early, succumbing to a nervous breakdown.

The man who saved the world now lives on a derisory pension of US$200 per month.

But the story may have a slightly more upbeat ending -- military secrecy meant that Petrov's actions only became public in 1998.

Since then, he has been the recipient of a number of awards and commendations -- and he will be the subject of a forthcoming documentary, entitled 'The Man Who Saved The World.'

For his part, Petrov is surprisingly modest about his pivotal role in preventing a global catastrophe.

"All that happened didn't matter to me -- it was my job." said Petrov.

"I was simply doing my job, and I was the right person at the right time, that's all.

"My late wife for 10 years knew nothing about it. 'So what did you do?' she asked me.

"I did nothing."