A satellite was indicating that the United States had fired five ballistic missiles at the Soviet Union. As Petrov told the BBC, "suddenly the screen in front of me turned bright red. It was piercing, loud enough to raise a dead man from his grave."
Just a few weeks before, on September 1, the Soviets had shot down a South Korean aircraft they claim they thought was a military plane, killing 269 civilians, including a U.S. congressman. Tensions were high and Petrov could have been forgiven for trusting the warning.
His orders were to pass the warning up the chain of command, which would approve the launch of a nuclear counterstrike that would have likely led to full-on nuclear war.
But he didn't. As he said later, he thought that it seemed odd that a U.S. nuclear strike was launched with just five missiles. What's more, he didn't entirely trust the new launch-detection system, only recently installed, and ground-based radars were failing to corroborate the launches, even minutes later.
"I had a funny feeling in my gut," Petrov said. "I didn't want to make a mistake. I made a decision and that was it."
A satellite was later discovered to be the culprit, mistaking the sun's reflection off the tops of clouds for a missile launch. The computer program that was supposed to filter out such information failed to do so.
After intense questioning by his superiors, the 44-year-old Petrov was initially praised for his decision. He says he was even promised a reward. But none came. He was later reprimanded over the filing of paperwork and reassigned. He says that the false alarm and subsequent bugs found in the early-warning system embarrassed high-ranking officers and scientists. He retired early from the service and later had a nervous breakdown.
In 2006, Petrov came to New York to receive an award at the United Nations from the Association of World Citizens for "the part he played in averting a catastrophe." In a statement, Russia's UN mission denied that any single person could have started or prevented a nuclear war.
But others have pointed out that under then-leader Yury Andropov, the Kremlin was obsessed with the idea of a surprise U.S. nuclear strike. "The danger was in the Soviet leadership thinking, 'The Americans may attack, so we better attack first,'" Oleg Kalugin, a former KGB chief of foreign counterintelligence, told the "The Baltimore Sun" in 2003.
-- Dan Wisniewski