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-29
Only five other submarines had attempted this trans-oceanic voyage during World War II: (April 1942), (June 1943), (October 1943) and the German submarines (August 1943) and (May 1945). Of these, "I-30" was sunk by a mine and "I-34" by the British submarine . Later, the famous Japanese submarine would also share their fate. In 1945 the German "U-234" had completed part of the voyage to Japan when news of Germany's surrender to the Allies was announced, and the submarine subsequently was intercepted and boarded off Newfoundland; this marked the end of the German-Japanese submarine exchanges.