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,
[2] and
his decision to disobey orders, against Soviet military protocol,[3] 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".