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-30
I-30 was a Type B1 submarine of the Imperial Japanese Navy during World War II. After operating in the Indian Ocean she participated in a "Yanagi" mission, aimed at connecting Japan and Nazi Germany by submarine. She was the first Japanese submarine to reach Europe, arriving at Lorient, France in August 1942. "I-30" returned to Singapore loaded with military technology and information, but hit a mine outside the harbour and sank. Only part of her cargo was salvaged.