Kriegsmarine U-boats 1939-45 (1) by Gordon Williamson. This, the first of two volumes on Germanys World War II U-boats, traces their development from the early U-boats of the Kaisers Navy, through the prohibition on German submarines following the Armistice in 1918 and the subsequent Treaty of Versailles, their secret development through 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 Type VIIA, Type VIIB, VIID, VIIE and VIIF Classes 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. Kriegsmarine U-boats 1939-45 (2) by Gordon Williamson.  This title follows the 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 in 1942 and launched in April 1944.  The first true submarine rather than submersible, the Type XXIs arrival was just too late to influence the war.  Other vessels featured are the Type XXIII, a technically advanced small vessel armed with only two torpedoes, and the Type X minelayers, which were more often used as supply boats than in their intended role.