By 1941, Winston Churchill had determined that the outcome of World War II rested on control of the Atlantic. Inspired by the game of Battleship, Captain Gilbert Roberts and a group of ten Wrens (as members of the Women's Royal Naval Service were called) devised a strategy game in an attempt to grasp the tactics behind the success of the German U-boats. Through play, the team developed "Operation Raspberry," a counter-maneuver that helped the Allies turn the tide in the Battle of the Atlantic. Simon Parkin blends lively storytelling with interviews and previously unpublished accounts to reveal the substantial role of these women in the defense of vital shipping.