Figure 1.-- The Japanese I-21 submaine torpedoed the tanker 'SS Montebello' off the coast of California, with imprtant oil fields, early in the War (December 23, 1941). There were such occasional sinkings of American merchant vessels during the Pacific War, but given the number of these vessels and the fact that they were not convoyed, they were very rare. Japanese orders and their captains' mindsets was to sink naval ships, not merchant vessels. Japanese commanders had little interest in a commerce war. Kriegsmarine liasons strongly promoted the idea, but the Japanese just were not interested. Iroinically, just such a commerce war conducted primarily by American submariners would cripple the Japanese war effort.

Naval historians fault the Japanese on their usage of the substantial submarine fleet in the Pacific War. The Japanese Navy never used their submarines in any serious effort to interdict American supply vessels. The American Pacific supply lines were long and vulnerable. They could have wreaked major damage or at the very least force the U.S. Navy to devote substantial resources to protect important maritime supply lines to Hawaii and Australia. A sustained commerce campaign would have forced the Allies to divert resources and probably have delayed the Allied buildups. Kriegsmarine liaisons advised the Japanese to do this, but the Japanese were adamant. It is unclear why the Japanese did not launch a campaign against supply lanes. The Army's insistence on using the subs to supply cut off bases was one factor. We suspect that the Code of Bushido was another factor. Naval commanders apparently simply did not think that attacking merchant vessels was the honorable role of a warrior. Rather the Japanese used their subs to target fighting ships. Here they had some successes in 1942, most notably against American carriers, but only rarely after that as American ASW capabilities being gained in the Battle of the Atlantic took hold in the Pacific. Japanese tactical deployment was also misguided. The Japanese at first used their submarines as scouts and to target warships. As the American offensive moved forward, however, the Japanese used their submarines to supply island garrisons that the Americans targeted for invasion. As the U.S. Navy built its force, Japan's ability to supply targeted garisonss with surface ships declined. They also used the subs to supply bypassed island garrisons, many of which were starving or near starvation by the end of the war. The bypassed garisons were turned into farmers. Not only were submarine supply missions wasteful given the limited cargo capacity of submarines, but operating in shallow waters around these islands exposed the submarines to attack. And Japanese submariners trasined for ttack wondered why they were delivering sacks of rice rather than firing torpedoes.

Created: 4:45 AM 6/7/2026
Last updated: 8:57 PM 6/7/2026