6th Fleet (Imperial Japanese Navy)
Despite these advantages, IJN submarines achieved remarkably little during World War II primarily having in hindsight suffered from the antiquated strategy of the Imperial Japanese Navy General Staff, who viewed submarines as little more than scouts whose main role was to locate and shadow enemy naval task forces in preparation for a decisive surface conflict. Maybe the IJN General Staff was slow to change as the submarines were generally slow to dive, easy to track with radar and sonar, difficult to maneuver underwater, and less sturdy than their German U-boat counterparts.
Japanese submarine I-124
The submarine was the fourth Japanese submarine lost in action in World War II. It has been surrounded in controversy since it was lost. In World War II there were claims that two submarines had been lost in the attack on Darwin; that its crew remained alive for some time; and that divers heard crew movement inside the hull. Later it was reported by both Japanese and American sources that "the "I 124" with her Division Commander Keiyu Endo, embarked, sank with all those on board in water only forty feet deep. US Navy divers were sent down and entered the submarine, and removed naval code books, a godsend for the Navy codebreakers at Pearl Harbor". However, this was later disproved by historian Dr Tom Lewis, in his book "Sensuikan I-124"; later re-published as "Darwin's Submarine I-124".