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.
Scuttling
To prevent a Soviet inspection team from examining surrendered Imperial Japanese Navy submarines after World War II, the United States Navy conducted Operation Road's End, in which it scuttled 24 of the submarines in the East China Sea off Fukue Island on 1 April 1946. Nine more Japanese submarines followed on 5 April, and another six went down by early May. In addition, U.S. Navy submarines sank four surrendered Japanese submarines as targets in the Pacific Ocean near Hawaii in May and June 1946, and the Royal Australian Navy sank six or seven (sources differ) surrendered Japanese submarines in the Seto Inland Sea on 8 May 1946 in Operation Bottom.