Operation Unthinkable was the name given to two related possible future war plans by the British Chiefs of Staff against the Soviet Union in 1945. The plans were never approved or 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 Western Allies" on the Soviets. "The will" was qualified as "a square deal for Poland", which probably meant enforcing the recently-signed Yalta Agreement. The planners decided that without massive American help Britain would probably fail. The assessment, signed by the Chief of Army Staff on June 9, 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 code name was now reused instead for a second plan, which was a defensive scenario in which the British were to defend against a Soviet drive towards the North Sea and the Atlantic following the withdrawal of the American forces from the Continent. At no time was either plan shared with the United States or anyone else. When the Labour Party came to power in July 1945 it ignored the draft plan. The study became the first Cold War-era contingency plan for war with the Soviet Union. Both plans were highly secret and were not made public until 1998 although a British spy for the Soviets, Guy Burgess, had passed on some details at the time.
Operations
Offensive
The initial primary goal of the operation was declared as "to impose upon Russia the will of the United States and the British Empire. Even though 'the will' of these two countries may be defined as no more than a square deal for Poland, that does not necessarily limit the military commitment". The chiefs of staff were concerned that given the enormous size of Soviet forces deployed in Europe at the end of the war and the perception that the Soviet leader Joseph Stalin was unreliable, there was a Soviet threat to Western Europe. The Soviet Union had yet to launch its attack on Japanese forces and so one assumption in the report was that the Soviet Union would instead ally with Japan if the Western Allies commenced hostilities. The hypothetical date for the start of the Allied invasion of Soviet-held Europe was scheduled for 1 July 1945, four days before the UK general election. The plan assumed a surprise attack by up to 47 British and American divisions in the area of Dresden, in the middle of Soviet lines. That represented almost half of the roughly 100 divisions available to the British, American and Canadian headquarters at that time. The plan was taken by the British Chiefs of Staff Committee as militarily unfeasible because of to an anticipated 2.5 to 1 superiority in divisions of Soviet land forces in Europe and the Middle East by 1 July, where the conflict was projected to take place. Most of any offensive operation would have been undertaken by American and British forces, as well as Polish forces and up to 10 divisions of the former GermanWehrmacht, remobilised from POW status. Any quick success would be caused by surprise alone. If a quick success could not be obtained before the onset of winter, the assessment was that the Allies would be committed to a protracted total war. In the report of 22 May 1945, an offensive operation was deemed "hazardous".
Defensive
In response to an instruction by Churchill of 10 June 1945, a follow-up report was written on "what measures would be required to ensure the security of the British Isles in the event of war with Russia in the near future". US forces were relocating to the Pacific for a planned invasion of Japan, and Churchill was concerned that the reduction in supporting forces would leave the Soviets in a strong position to take offensive action in Western Europe. The report concluded that if the United States focused solely on the Pacific Theatre, Britain's odds "would become fanciful". The Joint Planning Staff rejected Churchill's notion of retaining bridgeheads on the Continent as having no operational advantage. It was envisaged that Britain would use its air force and navy to resist, but a threat from mass rocket attack was anticipated, with no means of resistance except for strategic bombing.
Subsequent discussions
By 1946, tensions and conflicts were developing between Allied-occupied and Soviet-occupied areas of Europe. They were seen as being potential triggers for a wider conflict. One such area was the Julian March, and on 30 August 1946 informal discussions took place between the British and US chiefs of staff concerning how such a conflict could develop and the best strategy for conducting a European war. Again, the issue of retaining a bridgehead on the continent was discussed, with Dwight D. Eisenhower preferring a withdrawal to the Low Countries, rather than Italy, because of their proximity to the United Kingdom.
Possible Soviet awareness
In June 1945 senior Soviet Army commander Marshal Georgi Zhukov suddenly ordered Soviet forces in Poland to regroup and prepare their positions for defence. According to Edinburgh University professor John Erickson, Operation Unthinkable helps to explain why he did it. If the plans of the operation had been transmitted to Moscow by the Cambridge Five, that would explain the sudden orders to regroup and prepare for defence, however, it is just as possible that it was Soviet mistrust of Western Allies. If the Soviets had indeed known that the Western Allies were planning a possible attack, the element of surprise would have been lost before operations against the Soviets even began, further reducing the chances of Operation Unthinkable's success.
