In the second of this two-part series, David Hayman explores Germany's World War One U-boat threat and the fascinating and dastardly ploys Britain used against the submarines.

As the Great War began, the Royal Navy rushed to Orkney's great natural harbour, Scapa Flow. David Hayman uncovers the compelling characters of the little-known naval war - the cautious Admiral Jellicoe and the playboy Admiral Beatty. The story of great technologies and epic battles for control of the North Sea.