Operation Unthinkable

Operation Unthinkable was the name given to two related possible future war plans developed by the British Chiefs of Staff Committee against the Soviet Union in 1945. The plans were never implemented. The creation of the plans was ordered by British Prime Minister Winston Churchill in May 1945 and developed by the British Armed Forces' Joint Planning Staff in May 1945 at the end of World War II in Europe.

One plan assumed a surprise attack on the Soviet forces stationed in Germany to impose "the will of the United States and British Empire upon Russia". "The will" was qualified as "a square deal for Poland", but added that "that does not necessarily limit the military commitment". The assessment, signed by the Chief of Army Staff on 9 June 1945, concluded: "It would be beyond our power to win a quick but limited success and we would be committed to a protracted war against heavy odds". The same code name was thereafter reused instead for a second, marginally-related plan, a hypothetical defensive scenario by which the British were to defend against a Soviet drive towards the North Sea and the Atlantic Ocean after the withdrawal of the American forces from the Continent.