This book should serve as the basis of operations for many a military historian. It's the detailed story of British Naval Intelligence in operation during World War II with an emphasis on the crucial first four years. Room 39 was the hub, the center into which tons of information poured to be distilled, reexamined, evaluated in terms of plans, policy and rebuttal. Mr. McLachlan, who served on the personal staff of the Director of Naval Intelligence, Rear Admiral John Godfrey, from 1940 to 1945 details the action to the point of asphyxiation. But the persistent plodder can glean some interesting facts about personalities such as Ian Fleming, Churchill and Roosevelt operating under crisis conditions. Not to mention picking up a wide assortment of facts concerning the modus operandi of a global intelligence network. . . from the seventeen source material classifications on down. This shows the role of this division in locating and challenging U-boats, their brains behind the Normandy invasion, and the sinking of the Bismarck, etc. Bit of a rough go for the regular reader.