Admiral Sir Reginald “Blinker” Hall, the director of Naval Intelligence for most of World War I, was one of the outstandingif largely unrecognizednaval leaders of the war and this is a gripping study of this fascinating man and his invaluable legacy. Naval Intelligence’s ability to read and analyze German naval and diplomatic signals on a daily basis was a significant factor in the Allied victory, as the Germans never realized that their codes had been broken. The revelation of the Zimmermann Telegram, depicted as one of the most exciting events in the history of intelligence, was astutely handled by Hall and served as the catalyst that brought America into the war in April 1917. The effective interface between intelligence and operations, instituted by Hall and the antisubmarine chief, together with the introduction of convoys resulted in the defeat of the seemingly unstoppable U-boats. Hall’s dynamic leadership, talent for lateral thinking, and force of personality were essential to these successes, but above all, Hall was endowed with the guile and ruthlessness that kept him one step ahead of a formidable and determined enemy as well as their widespread espionage and subversion operations.