For the first time in naval warfare submarines played a major role in the war at sea in the years 1939-45, and this major reference book describes all the classes of vessel that were deployed by the eighteen combatant nations during those years. They were responsible for the sinking of 33 million tons of merchant shipping with the German and US navies achieving the greatest advantage with this devastating strategic weapon. Most of the countless books about submarines in WWII confine themselves to the boats of one particular navy or another: in this book every class of boat, from midgets to the large U-cruisers, of all the nations is covered in detail - more than 2,500 boats - and projected and experimental designs are also included. This furnishes the reader with an overall picture that allows for comparison between the technical and operational aspects of all the submarines that took part in the War. This is further helped by the inclusion of more than 400 illustrations. The author also outlines the evolution of the submarine and submarine warfare - including the interplay of wartime experience, design improvement and tactical innovation - thereby placing the subject in its true historical perspective. This new edition of a classic work has been completely redesigned and overhauled to make the most of the author's superb collection of photographs, and will appeal to a wide new audience for whom this important work has been unavailable for many years.