The triumphant true story of the young women who helped to devise the winning strategy that defeated Nazi U-boats and delivered a decisive victory in the Battle of the Atlantic. By 1941, Winston Churchill had come to believe that the outcome of World War II rested on the battle for the Atlantic. A grand strategy game was devised by Captain Gilbert Roberts and a group of ten Wrens (members of the Women's Royal Naval Service) assigned to his team in an attempt to reveal the tactics behind the vicious success of the German U-boats. Played on a linoleum floor divided into painted squares, it required model ships to be moved across a make-believe ocean in a manner reminiscent of the childhood game, Battleship. Through play, the designers developed "Operation Raspberry," a countermaneuver that helped turn the tide of World War II.