In early 1942, Britain was in a desperate situation.

The Royal Air Force had fought off Germany’s relentless onslaught in the Battle of Britain and much of the German army was fighting the Soviets in Eastern Europe, but the British remained isolated and at risk of being cut off from the world.

Hitler’s U-boats were wreaking havoc on Britain’s vital supply lines, and although the U.S. had entered the war on the side of the Allies, effective large-scale anti-submarine weapons and tactics were not yet fully developed or deployed.

Short of ships, material, and manpower, Prime Minister Winston Churchill turned to an audacious effort to combat the Kriegsmarine’s submarine wolfpacks: The Royal Navy would build a massive aircraft carrier out of ice and sail it to the middle of the Atlantic.