U-boat types of World War II Type Year of introduction Number of U-boats built Comments IA 1934 2 Fleet going ocean boat modeled on World War I designs IIA 1935 6 Prototype coastal patrol submarine IIB 1934 20 Improved coastal patrol submarine IIC 1937 8 Extended range coastal patrol submarine IID 1939 16 Long range coastal patrol submarine III 0 Design schematics created for a mine-layer submarine. Project was dropped due to design flaws IIIA 0 Prototype small boat carrier designed to hold two fast torpedo boats.