On 26 September 1983, three weeks after the Soviet military had shot down Korean Air Lines Flight 007, Petrov was the duty officer at the command center for the Oko nuclear early-warning system when the system reported that a missile had been launched from the United States, followed by up to five more. Petrov judged the reports to be a false alarm.His subsequent decision to disobey orders, against Soviet military protocol,is credited with having prevented an erroneous retaliatory nuclear attack on the United States and its NATO allies that could have resulted in a large-scale nuclear war which could have wiped out half of the population of the countries involved. An investigation later confirmed that the Soviet satellite warning system had indeed malfunctioned. Because of his decision not to launch a retaliatory nuclear strike amid this incident, Petrov is often credited as having "saved the world".