The success or failure of the Allies in WW II largely rested with success or failure of the landings in Normandy, France. And success or failure in Normandy largely rested with the element of surprise. The allied armies would be very vulnerable during and for a while after the landings. If counterattacked in force, their mission would likely fail. To ensure surprise, then, the Allies built several decoy armies to split German defense, and also carried out one of the most ingenious deception acts of the whole war.

On this day, April 30, in 1943, the submarine HMS Seraph surfaced off the Spanish coast and deposited the body of a transient found dead in a London subway, now dressed in a British intelligence officer’s uniform, into the water. The tide would take him to shore, they knew, where the German officers would “discover” to their fortune the top secret Allied invasion plans.

No detail was overlooked in creating the deception. “Officer William ‘Billy’ Martin” was given, a complete identity, including a wallet with love letters from his fiancee, theatre ticket stubs, and bills from several businesses Billy frequented. They went so far as to publish a fake obituary in the paper of him, in case the Germans would want to verify his identity with British sources. The plan were perfectly — as the British intelligence service reported to Churchill days later, “Mincemeat swallowed whole.”