Thirty years ago, on 26 September 1983, the world was saved from potential nuclear disaster.

In the early hours of the morning, the Soviet Union's early-warning systems detected an incoming missile strike from the United States. Computer readouts suggested several missiles had been launched. The protocol for the Soviet military would have been to retaliate with a nuclear attack of its own.

But duty officer Stanislav Petrov - whose job it was to register apparent enemy missile launches - decided not to report them to his superiors, and instead dismissed them as a false alarm.

This was a breach of his instructions, a dereliction of duty. The safe thing to do would have been to pass the responsibility on, to refer up.

But his decision may have saved the world....