This, the first of two volumes on Germany's World War II U-boats, traces their development from the early U-boats of the Kaiser's Navy, the prohibition on Germany having U-boats following the Armistice in 1918 and the subsequent Treaty of Versailles, the secret development of U-boats using a 'cover-firm' in Holland, culminating in the formation of the 1st U-boat Flotilla in 1935 with the modern Type II. The operational history section includes examples from the Classes Type VIIA, Type VIIB, VIID, VIIE and VIIF before concentrating on the mainstay of the U-boat arm, the Type VIIC. Comparisons are also made with the standard allied submarines, their strengths, weaknesses and U-boat tactics.

This title follows from New Vanguard 51: Kriegsmarine U-boats 1939–45 (1) and charts the continuing development of the U-boat in German service, including the evolution of the Type IX as a long range 'cruiser' intended for solo operations in distant waters. Also covered is the revolutionary Type XXI, conceived of in 1942 and launched in April 1944, the first true submarine rather than submersible, whose arrival was just too late to influence the war. Other vessels covered are the Type XXIII, a small vessel armed with only two torpedoes but technically highly advanced, and the Type X minelayers, which were rarely used in their intended role and more often used as supply boats.