"This paper traces the stages in U-Boat design and the reasons considered to have brought about these changes. Broad references are made to comparisons with British submarine designs. Details are given of the design particulars of the various classes of U-Boat from the commencement of the build-up of the German submarine force to the end of World War II. Numbers of submarines built, illustrating the enormous effort devoted to U-Boat production, are listed, together with a description of the methods of building pre-fabricated submarines. Notes are added on the features which have been most widely discussed in both press and naval circles, in particular the schnorkel."