The Imperial Japanese Navy in World War II possessed the most technologically advanced and varied submarine fleet in the world. Ranging from the largest pre-nuclear submarines in the world to manned torpedoes, with the fastest combat vessels and midget submarines operating alongside craft capable of carrying floatplane bombers, the fleet should have been an awe-inspiring and highly effective force. Yet, despite playing a crucial scouting role and being equipped with the best torpedoes available, the Japanese submarine fleet was surprisingly ineffective. With unique color plates, Mark Stille highlights the technical details of this diverse fleet, including the design successes and operational errors as well as investigating the underlying causes behind the failures of one of the greatest naval forces in the Pacific.