This title follows on from Volume I and charts the continuing development of the U-boat in German service. This includes the development of the Type IX as a long range 'cruiser' intended for solo operations in distant waters. Despite its drawbacks, the Type IX was highly successful in long distance operations, particularly at operations off the US coast and in the Caribbean/South Atlantic. The revolutionary Type XXI, conceived of in 1942 and launched in April 1944. The first true submarine rather than submersible. Its arrival was just too late to influence the war. The Type XXI had only a brief sell in actual operations and never sunk any enemy ships, but it did make a dummy attack just as the cease-fire was given and entered undetected into a British Battlegroup with a major Battleship dead in his sights. Also included is the Type XXIII, small and armed with only two torpedoes, but technically highly advanced - so much so that some scuttled boats were raised and served in the post war West German Navy. The Type XXIII did have some operational usage and sunk allied vessels. The Type X minelayers (only eight were built) were rarely used in their intended role, though some successes were achieved. They were more often used as supply boats including a long distance mission to Japan carrying uranium for the Japanese nuclear research programme. Finally a brief look is taken at some of the experimental designs that were actually built, but were still under development at the end of the war, such as the Walter turbine-driven boats and the various midget submarines.