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 & 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 & enjoying several notable successes it was surprisingly ineffective. Using unique color plates Mark Stille describes the astounding technical advances of this range of vessels & the wartime tactics responsible for their failure.