VIII 0 Intended as a fast attack submarine. Never went beyond initial designs IX 1936 8 First post World War I long range fleet ocean boat IXB 1937 14 Standard pre-World War II fleet ocean boat IXC 1939 54 Upgraded fleet ocean boat used in the opening years of World War II IXC/40 1940 87 Enhanced fleet ocean boat with better diving abilities IXD1 1940 2[1] Heavy diesel boat, suffered from numerous design flaws.