Japan’s Puzzling Failure in Anti-Submarine Warfare During World War II

Early in 1945 the Japanese war machine was in a sorry state: “American submarines and aircraft destroyed in four years almost all of Japan’s merchant fleet. It was radically defeated even before American bombs incinerated the cities and Roosevelt obtained the entry into the war of the Soviet Union.”(1) Immediately after the surrender, the Japanese government confessed that shipping losses were the main reason behind defeat.(2) Japanese failure to protect its merchant fleet and thwart the U.S. submarine campaign was a decisive turn of the tide in World War II that sealed Tokyo’s fate. What made Japan’s anti-submarine warfare (ASW) effort during World War II so unsuccessful?

Japan is, like Britain, an insular country. Hence, like the British, the Japanese should have devoted an intense effort to countering the threat posed by enemy submarines. Successful enemy submarine warfare could have imposed ― and indeed did impose ― a painful blockade on the country. The failure of the Japanese to acknowledge this threat of strangulation is puzzling.

I argue here that Japan’s failure to respond to the submarine threat resulted from the Imperial Japanese Navy’s (IJN) deliberate policies to expand its resource base at the expense of the Imperial Japanese Army. Analysts concerned with Japan’s failure in ASW often fall back on cultural explanations,(3) but I will follow Orbach in focusing on the military’s bureaucratic politics.(4) Unfortunately, few have paid attention to Japanese ASW effort, as shiny objects like carriers and battleships usually steal the spotlight.

In the first part, I explain why Japan could not have ignored its vulnerability to submarine attacks. Hence, the ASW failure cannot have resulted from sheer negligence or lack of warning. The second part is a brief account of the evolution of Japan’s ASW problem during World War II. The third part examines the causes of the IJN’s policies that led to this disaster.

Japan Could Not Have Ignored the ASW Problem

When it decided to attack America, the Japanese government gravely underestimated its logistical problems. Before the war, Japan had to import 10 million tons of products annually for its military industry and economy to function normally. But its merchant fleet could ship only up to 6 million tons. Therefore, 40% of the importations depended on foreign shipping. Tokyo imported 90% of its oil, most of its iron, coal, food, and rubber. Only silk was not imported.(5) It should have been evident to Japanese planners that submarines would severely threaten the archipelago’s supply lines.

During World War I, German submarines wrought havoc on Allied shipping. For example, late U-boats such as the UC II were already formidable war machines, carrying both torpedoes and mines. The Japanese had around 25 years to comprehend the implications of the nascent submarine warfare.(6) Moreover, closer to Japan, the Soviet Union began to deploy an impressive submarine force. A mortal foe of Japan investing heavily in submarines should have set off alarm bells in Tokyo.

In fairness, the Japanese were not totally blind to the issue. Students at Japan’s Imperial War College had to study the memoirs of Winston Churchill and Lloyd George, especially the parts related to ASW.(7) Before Pearl Harbor, they assessed based on World War I data that they would lose between 800,000 and 1,100,000 gross tons of shipping capacity for the first year and between 700,000 and 800,000 gross tons for the second and third years of a war. But this assessment was far too optimistic. They used World War I figures but forgot that those low numbers came from the Allies’ prowess in ASW.(8) The situation in the Atlantic during the first months of World War II should also have alarmed the Japanese. The Allies had already lost 4,000,000 gross tons of shipping capabilities by the end of 1940. This would have represented two-thirds of Japan’s merchant fleet.(9) From 1943 to 1945, the Germans deployed a fleet of U-boats ― the Monsun Gruppe ― to the Moluccas to help the Japanese in their naval struggle against the Allies. Thus, Japanese and German navies fought together in the Indian Ocean. This submarine fleet was composed of 11 U-boats and other vessels and was based in Penang (Malaysia) and Surabaya (Indonesia), with smaller docks in Singapore and Jakarta (Indonesia).(10) Through this cooperation, the Japanese could benefit from Germany’s long and extensive experience in submarine warfare. They could follow the evolution of submarine warfare in the Atlantic theater through first-hand accounts and acquire valuable knowledge about how to defend against Allied submarines.

Japanese Failure During the War

Starting in the 1930s, Japan threw all its resources at building a massive surface fleet able to win a decisive battle against the United States Navy.(11) Consider the Yamato-class battleship, the biggest and most powerful battleships in history. Two ships, the Yamato and its sistership the Musashi, were put into service in 1941 and 1942, respectively. These monsters had a full-load displacement of 73,000 tons and boasted nine 460mm main guns, the biggest guns ever mounted on a boat. But these ships were so precious that the Navy was reluctant to use them in battle until 1944 when it had no other option left to push back the U.S. Navy.

The IJN realized too late that those giant battleships were vulnerable to submarine and air attacks. The Japanese should have learned this lesson from the fate of the Bismarck, Germany’s giant battleship and jewel of the Kriegsmarine. It was immobilized by British Swordfish torpedo bombers before being finished off by surface ships on 27 May 1941, a few months before the Yamato entered into service. Those battleships were designed to hunt other ships on the high seas in Jutland-like battles. It was clearly an offensive ship, not intended for defensive operations. It exemplifies the IJN’s inherent bias for offensive operations. The resources used to build and maintain those gigantic ships would have probably been better invested in protecting Japan’s vital sea lines of communication (SLOC).(12)

U.S. submarines usually departed from Perth (Australia) and entered the Japanese perimeter through the South China Sea to sink Japanese vessels.(13) However, the United States was badly short on torpedoes after Pearl Harbor. Although traditional ship hunting occurred, these submarines mainly served for laying mines into Japanese waters. From February 1943, the Allies began to lay mines by airdropping, a more efficient method allowing them to mine inland waterways throughout the Japanese empire ― riverways were a far too dangerous place for sending submarines.(14) Due to the extensive mining of coastal areas, Japanese ships had no other way than to venture into the high seas, where American subs could then hunt them down.(15)

In the Atlantic, German submarines departed from the Bay of Biscay to attack Allied shipping. Although this bay is almost too large to call a bay, the Allies conducted a successful ASW campaign. Contrary to German submarines, U.S. submarines departing Perth to the South China Sea had to pass through several tiny chokepoints easy to control and close ― namely the Balabac, Karimata, Mindoro, and Gaspar Straits. The East China Sea and the Sea of Japan, both vital to Japanese shipping, also presented numerous islands and chokepoints that could have helped the Japanese ASW effort.(16) But even with a more favorable geographical situation, the Japanese failed to emulate Allied successes in the vast Atlantic Ocean. 

Tokyo introduced only at the end of 1942 a regulation for the security of merchant ships and started escorting merchant ships only in 1943. The Grand Escort Command Headquarters was established in November 1943. However, Japan’s few ASW assets were usually diverted toward the frontline and away from interior SLOC. The rear line service requested 360 ASW frigates, but the Navy only accorded 40.(17) The IJN wanted the shipyards to focus on building more offensive vessels, such as aircraft carriers, submarines, and transport vessels.

Reluctantly, it finally agreed to create two escort groups to protect merchant shipping. Those two groups had 14 old destroyers and 10 smaller ships. It was far from sufficient for the task. Moreover, shipping authorities disliked convoy tactics because the incurred loss of speed would decrease the overall efficiency of the shipping circulation.

During the Guadalcanal battle, Japan diverted numerous merchant ships to the Solomon Islands, where they were easy prey for enemy submarines. From January 1943, Japan’s shipping situation would only worsen. The Americans put tremendous effort into expanding their submarine warfare capacities. The U.S. submarine onslaught on Japanese ships truly began in August 1943. Japanese companies and civilians began to feel the lack of imported products. Although the government decided to retreat behind a more westward defensive line and preserve its shipping capacities, the Navy kept committed to its losing fight around the Solomons and did little to protect Japanese SLOC.

The Grand Escort Command was finally created in November 1943 to stop this disaster. Planners hoped it would be powerful enough to offset the Combined Fleet hawks’ offensive bias. An influential senior admiral was appointed as its commander-in-chief. But he had under his command a tiny fleet of mostly obsolete ships. Its more efficient vessels often ended up transferred to the Combined Fleet. Despite protests, the Navy kept assigning to escort missions graduates from civilian marine schools and not military-trained officers. For instance, the Command was forced to rush into combat in January 1944 a naval aviation group with no prior skill or experience in ASW. In terms of personnel and equipment ― particularly radars and radios — the Combined Fleet was still largely favored.

In January-February 1944, submarines sank Japanese ships at a rate of around 250,000 gross tons per month. Pictured with this article is the U.S.S. Gato, the lead ship in it's class of highly effective submarines. This slaughter finally pushed Japan to adopt large convoy tactics. In May-June 1944, U.S. submarines turned the tide of the Battle of the Philippine Sea by sinking four destroyers and two carriers. Hence, during this battle, submarines sent the two best Japanese carriers to the bottom and killed the few hopes left in Japan. After the Japanese began forming convoys, the Americans reacted by using wolf-pack tactics, thus nullifying these countermeasures.

Notwithstanding that Japan was heading for a disaster, the High Command was still planning for battleship offensives against the U.S. fleet, although it was apparent by mid-1944 that the Americans had a decisive superiority in the Pacific.(18) Japan only used its aircraft carriers in an offensive way, with very few successes after Pearl Harbor.(19) These carriers may have been more useful in a defensive ASW orientation.

In August 1944, the Grand Escort Command lost its autonomy and was attached to the Combined Fleet Headquarter, leading to further negligence of ASW with disastrous results. By the fall of 1944, ASW was no longer a primary concern for shipping security; as the Americans approached the Japanese homeland’s coasts and mainland Asia, SLOC became the targets of all types of attacks, not only from submarines but also from surface ships and aircraft. Although Japan tried to bolster somehow its ASW efforts, everything was already lost.(20)

As the war progressed, Japan attempted to reorient some supply lines from waterways to overland roads. However, overland transport was costlier and subjected to sabotage, destroyed bridges, and air attacks. The situation of supplies became so dire that the Japanese even lacked carbide, the material used for repairing damaged ships. From November 1944, any severely damaged Japanese ship was definitively out of action since it was impossible to fix.

On the Japanese side, a total lack of coordination is apparent. For instance, nobody asked the experts at Tokyo University to develop mine clearance methods and technologies before Spring 1945, too late to change the course of the war.(21) It contrasts sharply with Britain, which invited in mid-1942 scientists led by Nobel prize winner Professor Blackett to work on the submarine threat to Allied shipping.(22)

The casualty figures are impressive. In 1942, American submarines sank 139 Japanese merchant vessels, totaling 560,000 tons. In 1943, they sank 305 vessels, totaling 1,335,000 tons. In 1944, 565 vessels, totaling 2,480,000 tons, were sunk. Finally, in 1945, American submarines sank 163 vessels, totaling 440,000 tons. All types of ships included, the total Japanese shipping lost to U.S. submarines amounted to 5,320,094 tons (among them 90% of merchant vessels). Overall, submarine attacks killed around 67,000 Japanese merchant officers and personnel.(23)

How to Explain Such a Failure?

Why did Japan fail to prepare for anti-submarine warfare? A first reason sometimes suggested is cultural bias. Prior to the war, Japan seriously underestimated the Americans, their capabilities, and their willingness to fight. Prime Minister Tojo considered the American people “undisciplined, unmilitary, and unconcerned with anything but the pursuit of the jazzy life.”(24) But this is a weak explanation for all Japanese failures and mistakes.

According to Horie, the Japanese people have an inherent preference for the offensive. Moreover, he points out the lack of questioning of the authority in the traditional Japanese system as a cause of Japanese failures.(25) However, the preference for the offensive is widespread. It is even hard to find a country that privileges defensive operations.(26) The lack of questioning of the authority does not explain the failure of said authority in the first place. Those two arguments are rather unconvincing.

Oi explains that Japan developed a bias for fleet-versus-fleet actions from the Sino-Japanese War (1894–1895) and the Russo-Japanese War (1904–1905).(27) Indeed, the Japanese scored a long series of surface-battle victories between 1894 and 1942, thus skewing the IJN toward overfocusing on surface warfare. But this argument does not close the debate either. During both World Wars, submarines were still an emerging technology. Virtually all Navies around the world continued focusing on surface-fleet warfare. Britain, too, had a bias for fleet-to-fleet engagements before World War II, and this despite its experience during the last conflict. The Battle of Jutland in 1916 was the British equivalent of Takeshima for the Japanese: an event which ossified military doctrine into a battleship-focused doctrine. However, they were able to learn very quickly.(28) Why would only Japan have developed such an entrenched bias that it forgot ASW?

These cultural or historical arguments are not necessarily wrong, but culture and history do not produce policies per se. They can only influence policies through the intermediary of an institution. Bureaucratic politics better explains why Japan focused on platforms and strategies that fitted offensive operations, such as aircraft carriers or giant battleships. Anti-submarine warfare is a fundamentally defensive endeavor. Meanwhile, military organizations tend to be offensive-oriented so they can increase their resources. Offensive strategies generally require more troops, weapons, and organizational autonomy than defensive ones. Therefore, militaries prefer to emphasize offensive options so they can ask for additional budget and resources from the government. Indeed, defensive ASW requires less means than offensive capital-ship operations.(29)

Japan viewed prior to the war its main enemies as China and the Soviet Union. A big part of Japanese military expenditures was therefore directed to the Army, while the Navy was struggling with the spare budgetary remains.(30) The Japanese command system was based on the ‘prerogative of the supreme command’ principle. The Emperor was not always fully aware of the actual situation on the ground since the Army and the Navy only reported what they wanted ― usually their successes ― and were very independent. Before World War II, the Army was the strongest of the two, even if the cabinet had little influence on both.(31) But Pearl Harbor changed that, allowing the IJN to increase its clout and decrease the Army’s.

After December 1941, the Navy pushed for continued expansion in the Pacific and Southeast Asia, while the Army favored attacking Russia as soon as feasible. After the initial victories in Southeast Asia, the Navy launched new offensive operations in the Pacific. A land war against the Soviets would have diverted resources from the Navy to the Army, so the Navy launched further attacks all around to force the government to focus on the IJN. Furthermore, because those faraway attacks required massive shipping capacities, Japan lacked the ships to sustain new Army commitments to mainland Northeast Asia.

Army transport ships were among the main victims of Allied submarines. This bolstered the Navy’s importance even more since the Army had to rely more on the Navy to protect its ships. When the Army complained about the situation, nothing was done.(32) The IJN developed plans to seize Hawaii, and even Australia, but the Army’s resistance pushed Japan toward less ambitious ― although still too ambitious ― conquests in the Pacific. Those conquests created long and indefensible SLOC, easy targets for American submarines. Despite that, major fleet actions were still favored over SLOC defense since they were higher profile and more glamorous to the public than ASW operations.

At the Naval General Staff, around 10 officers were assigned to the Combined Fleet operations, while only one officer was assigned to the rear-line defense operations ― shipping protection and ASW. With the war in sight, only one more officer was assigned to the position, making a total of two people in charge of protecting the Japanese SLOC. This is stunning if one compares with the British ASW effort during World War II. The Combined Fleet’s operations were always favored over everything else, at the neglect of ASW.

Japan thus lost its anti-submarine war because of a Russian doll-like series of bureaucratic biases: the Navy over the Army, the Combined Fleet over shipping protection, and finally, fleet-versus-fleet warfare against other forms of combat. The IJN was so powerful that it imposed on the country its preferred strategy: conquering almost all of the Pacific and Southeast Asia and destroying U.S. naval power in massive, decisive battles. Of course, Japan did not defeat itself; I do not discount the Allied forces’ excellence against this formidable and determined adversary. But the IJN’s homemade strategy resulted naturally in a flawed doctrine overemphasizing big battleships and carriers’ offensive operations. It led to the fateful negligence of anti-submarine warfare and turned the tide of the Pacific War.