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.
Monsun Gruppe
The German invasion of the Soviet Union in 1941 had ended the use of overland routes which were for the delivery of strategic materials from southeast Asia, and few Axis ships were able to avoid Allied patrols of the North Atlantic. Japan was interested in exchanging military technology with Germany, the Japanese submarine "I-30" initiated the submerged transport of strategic materials in mid-1942 by delivering 1500 kg of mica and 660 kg of shellac. Japanese submarines designed for the vast distances of the Pacific were more capable transports than the compact German U-boats which were designed for operations around coastal Europe; but large Italian submarines had proved ineffective for convoy attacks. The Italian Royal Navy ("Regia Marina") converted seven Italian submarines operating from BETASOM into "transport submarines" in order to exchange rare or irreplaceable trade goods with Japan. They were: The "Bagnolin", the "Barbarigo", the "Cappellini" (renamed "Aquilla III" in May 1943), the "Finzi", the "Giuliani", the "Tazzoli" and the "Torelli".