The name of the operation is somewhat laughable given the conclusions the study reached. The War Ministry christened the plan "Operation Unthinkable". The planned offensive against the Soviet Union had the goal of hindering Soviet power and influence in the post war European power paradigm. Churchill was not eager to replace totalitarian Nazism with totalitarian Communism in many of the central and eastern nations "liberated" by Soviet troops. Churchill intended instead to remove the foot in the door that Stalin now had in states like Germany, Czechoslovakia, Austria, Hungary, and Poland. He slated July 1st as the date where the operation would commence and ordered plans to be drawn up immediately. The plans were not released to the public until 1998 and were somewhat shocking.
The operation was given a very poor chance of total success (hence why the name is comical to me) when the analysis and plan were delivered to the prime minister. The fact was this...the Soviets had a 4 to 1 advantage in men over the British Commonwealth (U.K. and Canadian) and American forces currently in mainland Europe and a 2 to 1 advantage in tanks. The plan did call for half of all Allied power, roughly 47 divisions (1.25 million men), to attack in the center of the Soviet line near Dresden in Germany and then encircle and destroy as many units as possible in order to push the Soviets back into the USSR if at all possible. In addition to the American and Commonwealth troops, Churchill included that select units of the German Wehrmacht should be re-armed and added to the force with numbers of German troops being around 100k strong at the outset. This is interesting because it did provide proof of the long rumored secret negotiations during the wars last days between Heinrich Himmler and the west for an peace and alliance against the Soviets. The British did indeed listen to and briefly consider the offer as they considered Stalin a future danger. Churchill's hatred of Nazism and the reports of Nazi war crimes quickly ended any consideration of working with the Nazis.
One thing that killed Operation Unthinkable besides the risk of a protracted total war was the fact the Americans were going to be shifting troops to the Pacific for the planned invasion of the Japanese home islands. So American troop numbers would likely be much lower when the offensive commenced, making Soviet superiority in numbers even more of a challenge to overcome. There were also worries of a Soviet and Japanese alliance should the west attack Stalin. Ultimately the plan was shifted to a defense against Soviet aggression as the political climate at home quickly turned against Churchill. His sabre rattling against the USSR found little traction with the war weary British public who would continue to suffer economically well into the 1950's with rationing and rebuilding. Churchill was voted out of office the same month the operation was to commence, and his speeches against the USSR found popularity in America instead where for years he was seen as a champion against communism until his return to power in 1951.
There is no telling how the addition of the A-bomb would have changed the plan and its outlook for success (it was not used until August 1945). It most certainly checked the aggressive tendencies of the Soviet Union for the remainder of Stalin's rule. Even after the USSR ended the atomic monopoly of America in 1949 with the first test of their fission bomb, the American atomic arsenal was superior to the Soviets in numbers, and the resulting firepower gap left Stalin apprehensive to move in the west, he instead supported efforts in Asia. These efforts resulted in the Chinese going communist that same year followed by Russian air and material support in the Korean Conflict of 1950-1953. So Operation Unthinkable was never used, and instead has left historians to think about the "what if" questions had it been used.
|Churchill firing US Tommy Gun|
|Churchill firing U.S. M1 Carbine|
|Churchill during the Battle of Britain arming himself against a possible German invasion|