Able Archer 83 was a ten-day NATO exercise starting on November 2, 1983 that spanned the continent of Europe and simulated a coordinated nuclear release.Fischer, "A Cold War Conundrum" It incorporated a new, unique format of coded communication, radio silences, participation by heads of state, and a simulated DEFCON 1 nuclear alert. The realistic nature of the exercise, coupled with deteriorating relations between the United States and the Soviet Union and the anticipated arrival of "super-stealth" Pershing II nuclear missiles in Europe, led some in the USSR to believe that Able Archer 83 was a genuine nuclear strike.Andrew and Gordievsky, Comrade Kryuchkov's Instructions, 85-87; Beth Fischer, Reagan Reversal, 123,131; Pry, War Scare, 37-39; Fischer, "A Cold War Conundrum" In response, the Soviets readied their nuclear forces and placed air units in East Germany and Poland on alert.Oberdorfer, A New Era, 66; SNIE 11-10-84 “Implications of Recent Soviet Military-Political Activities” Central Intelligence Agency, 18 May, 1984 This relatively obscure incident is considered by many historians to be the closest the world has come to nuclear war since the Cuban Missile Crisis of 1962.