During World War II, the Imperial Japanese Navy was at the forefront of submarine technology. It fielded the largest pre-nuclear submarines in the world, some capable of carrying floatplane bombers, which operated alongside fast combat vessels and midget submarines, all equipped with the best torpedoes available. The Japanese submarine fleet should have been an awe-inspiring force but, despite playing a crucial scouting role and enjoying several notable successes, it was surprisingly ineffective. Using unique color plates, Mark Stille describes the astounding technical advances of this range of vessels, and the wartime tactics responsible for their failure.