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-124
The submarine was the fourth Japanese submarine lost in action in World War II. It has been surrounded in controversy since it was lost. In World War II there were claims that two submarines had been lost in the attack on Darwin; that its crew remained alive for some time; and that divers heard crew movement inside the hull. Later it was reported by both Japanese and American sources that "the "I 124" with her Division Commander Keiyu Endo, embarked, sank with all those on board in water only forty feet deep. US Navy divers were sent down and entered the submarine, and removed naval code books, a godsend for the Navy codebreakers at Pearl Harbor". However, this was later disproved by historian Dr Tom Lewis, in his book "Sensuikan I-124"; later re-published as "Darwin's Submarine I-124".