Petrov Day

Petrov Day named by Stanislav Yevgrafovich Petrov (Russian: Станисла́в Евгра́фович Петро́в; born c. 1939). 

On September 26, 1983, he was the duty officer at the command centre for the Oko nuclear early-warning system when the system reported that a missile was being launched from the United States. Petrov judged the report to be a false alarm, and his decision is credited with having prevented an erroneous retaliatory nuclear attack on the United States and its NATO allies that could have resulted in large-scale nuclear war. Investigation later confirmed that the satellite warning system had malfunctioned.

http://lesswrong.com/lw/jq/926_is_petrov_day/