Ultra's Arctic war

"The Arctic convoys that took vital supplies at enormous risk to Russia during the Second World War did so within range of Germany's Luftwaffe, surface ships and U-boats. These convoys were watched over by Bletchley Park codebreakers and intelligence officers, through decrypts of the German Enigma coding machine. In particular, these decrypts were closely involved in three of the key actions of the Arctic battles, the sinking of the battlecruiser Scharnhorst, the destruction of the battleship Tirpitz and the disastrous PQ17 convoy. This book examines the Ultra decodes, and for the first time lists the key details in these events in chronological order, detailing the role of the decrypts in a virtual minute-by-minute breakdown of how the signals were used in these key actions."