The primary goal of the operation was declared as follows: "to impose upon Russia the will of the United States and the British Empire." (The word "Russia" is used heavily throughout the document, although at the time Russia as a political entity had been replaced by the Soviet Union.)
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 existed a Soviet threat to Western Europe.
Churchill stated within the briefing documents for Unthinkable that it was a "precautionary study" of what he hoped was a "purely hypothetical contingency". The plan was rejected by the British Chiefs of Staff Committee as militarily unfeasible.