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.
History of submarines
Meanwhile, the Imperial Russian Navy (IRN) purchased German constructed submersibles built by the Germaniawerft shipyards out of Kiel. In 1903 Germany successfully completed its first fully functional engine-powered submarine, "Forelle" (Trout), It was sold to Russia in 1904 and shipped via the Trans-Siberian Railway to the combat zone during the Russo-Japanese War.