<p>The breaking of the Enigma machine is one of the most heroic stories of the Second World War and highlights the crucial work of the codebreakers of Bletchley Park, which prevented Britain's certain defeat in 1941. But there was another German cipher machine, used by Hitler himself to convey messages to his top generals in the field. A machine more complex and secure than Enigma. A machine that could never be broken. For sixty years, no one kne...