Submarines of the Imperial Japanese Navy
The Imperial Japanese Navy's doctrine of fleet warfare ("guerre d'escadre") resulted in its submarines seldom posing a threat to allied merchant convoys and shipping lanes to the degree that the Kriegsmarine's U-boats did as they pursued commerce raiding against Allied and neutral merchant ships. During the war, IJN submarines did sink about 1 million tons (GRT) of merchant shipping (184 ships) in the Pacific; by contrast U.S. Navy submarines sank 5.2 million tons (1,314 ships) in the same period, while U-boats of Nazi Germany's "Kriegsmarine", the IJN's Axis partner, sank 14.3 million tons (2,840 ships) in the Atlantic and other oceans. During the last two years of the War in the Pacific, many IJN submarines were also occupied serving to transport supplies to isolated island garrisons, ones that had been deliberately bypassed by the Americans and the Australians and which could not be reached by surface transports because of blockade by Allied warplanes and naval vessels.
Japanese submarine I-8
The Japanese submarine "I-8" was a World War II Junsen Type J-3 Imperial Japanese Navy submarine. The vessel, along with "I-7", were the largest Japanese submarines to be completed before the outbreak of the Pacific War. It was based on the KD ("Kaidai") type. Both submarines participated in the attack on Pearl Harbor, they also conducted patrol missions with Yokosuka E14Y seaplanes.
In 1943 "I-8" completed a technology exchange mission by sailing to German occupied France and back to Japan. Under a new commander later in her career, the submarine's crew committed several war crimes in the latter period of the second world war.