During WWII, the U.S. Playing Card Company joined forces with American & British intelligence agencies to create a deck and help Allied prisoners of war escape from German camps. When this Ace of Spades is soaked in water, it separates to reveal a piece of a map inside. An agent would need more cards to piece together a whole map.
To date, decks of these cards are said to have helped at least 32 people escape from Colditz Castle and prompted some 316 escape attempts. No one knows for sure how many decks were produced, but the only two known surviving decks are here at the Spy Museum.
