The naval side of the Enigma story and breaking the seemingly impregnable German codes during World War II is the focus of this book. Although cryptanalysts managed to unlock the codes of the German army and the Luftwaffe, they needed U-boat Enigma machines and code books to solve the more complicated naval version. This book analyzes the development of Enigma, its role during U-boat operations, and the subsequent codebreaking work at Bletchley Park. The author examines all U-boats known to have been boarded by the Allies during the war from which Enigma machines could have been captured.