The story of how British naval intelligence was able to break German naval codes in World War I is fully explored by the noted U-boat historian Robert Grant. Examining radio interception records, telegrams, and the records of the Admiralty salvage department, Grant has unearthed an amazing tale of resourcefulness and danger. Along with collecting cipher information from many differing sources, intelligence personnel in Room 40, the nerve center in the Admiralty, sent Royal Navy divers to collect data from U-boat wrecks around Great Britain and Ireland and had ground crews comb through the wreckage of crashed zeppelins. Their efforts paid off. With their new-found insights into U-boat operations, the "men of Room 40" could hunt down and destroy U-boats at sea. This intriguing look at early successes in deciphering U-boat codes is sure to join the author's previous work as a standard reference on U-boat warfare. It includes an updated list of German submarines sunk or interned.