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.
Submarines of the Imperial Japanese Navy
Only six submarines attempted this trans-oceanic voyage during World War II: (mid-June to August 1942), (June 1943), (October 1943), (November 1943), and German submarines (August 1943) and (December 1944). Of these, "I-30" was partially successful but was later sunk by a mine, "I-8" completed her mission, "I-34" was sunk by British submarine , and "I-29" by the United States submarine, (assisted by Ultra intelligence). made the final attempt.