As Allied forces laboriously clawed through shattered Europe at the end of WWII, some in the British military had their eyes on something even more far-flung. Dubbed Operation Unthinkable, this astonishing plan envisioned a full-scale attack on the Soviet Union. It was a plan that would see Western and Polish army divisions join forces to drive into Poland and then onward to Germany in an attempt to free Eastern Europe from Soviet control, thus undermining Stalin’s power and perhaps bringing down his regime altogether.

The plans were drafted in utmost secrecy with only Churchill’s top commanders knowing of its existence. But even at that stage, many were horrified by it. Field Marshal Alan Brooke, for example, argued that attacking the Soviets so soon after the end of such a brutal war would be ‘catastrophic’ for morale. The Russians had done the lion’s share of the fighting and suffered untold misery in the process, and to hit them again so soon would be a major blow to their already shattered spirits.

Besides, there was also the issue of logistics. The Soviets outnumbered the combined British and American land forces by more than two to one, and a successful invasion into Eastern Europe would have required the use of air and naval forces in addition to ground troops. What’s more, the Soviets knew that an attack on Poland was being considered, so if the operation went ahead it could potentially ruin the element of surprise.