How close did the Cold War come to nuclear annihilation?

The answer

On September 26, 1983, Soviet officer Stanislav Petrov received satellite alerts indicating five incoming U.S. nuclear missiles. Standard protocol demanded immediate retaliation, which would have triggered full-scale nuclear war. Petrov judged it a false alarm - reasoning that a genuine first strike would involve hundreds of missiles, not five - and chose not to report it upward. He was right: sunlight reflecting off clouds had fooled the satellite sensors. A similar near-miss occurred during the 1962 Cuban Missile Crisis when a Soviet submarine nearly launched a nuclear torpedo.