Colonel Petrov attributed his judgment to both his training and his intuition. He had been told that a nuclear first strike by the Americans would come in the form of an overwhelming onslaught.

“When people start a war, they don’t start it with only five missiles,” he told The Post.

Moreover, Soviet ground-based radar installations — which search for missiles rising above the horizon — did not detect an attack, although they would not have done so for several minutes after launch.

Colonel Petrov was at first praised for his calm, but in an investigation that followed, he was asked why he had failed to record everything in his logbook. “Because I had a phone in one hand and the intercom in the other, and I don’t have a third hand,” he replied.

He received a reprimand.

The false alarm was apparently set off when the satellite mistook the sun’s reflection off the tops of clouds for a missile launch. The computer program that was supposed to filter out such information had to be rewritten.

Colonel Petrov said the system had been rushed into service in response to the United States’ introduction of a similar system. He said he knew it was not 100 percent reliable.

“We are wiser than the computers,” he said in a 2010 interview with the German magazine Der Spiegel. “We created them.”

Cold War tensions persisted. In November 1983, NATO carried out Able Archer 83, a big military exercise simulating a coordinated nuclear attack. The exercise, alongside the arrival in Europe of Pershing II nuclear missiles, led some in the Soviet leadership to believe that the United States was using it as a cover for war; the Soviets placed air units in East Germany and Poland on alert. (Able Archer is the backdrop for the recent television series “Deutschland ’83.”)