Figure 1.--Japan entered World War II with a large submarine service, but unlike other fleet elements, poorly built ships. They had, however, what American submariners lacked--a highly reliable torpedo. The Japanese submariners scorded some successes, but given the size of the force was not a major factor in the Pacific War. This was in sharp contrast to the key role played by American submariners who after the torpedo problem was fixed were aided by both Ultra decrypts and radar. The American submariners decimated the Japanese maru fleet, disrupting the country's war economy. Japanese submariners considered sinking frighters almost beneath their dignity. Their mind set was that was not jat true warrios did. Here two Japanese submarines surrender 200-mikes off Tokyo (August 31, 1945). The wire service transmission from Guam read, "Jap subs surrender to U.S. Navy: Two Japanese submarine which surrendered to American naval forces 200 miles from Japan display the American flag over the emblem of the rising sun on their masts. Both subs were coated with an asphalt material to minimize detection by radar." The Germans had developed a more sophisticated technology, but by the time it was perfected the U-boat fleet had been severely depleted.

The Japanese Navy got its first submarines from the United States, buying them from the Electric Boat Company in the early 20th century. More sophisticated submarines were obtained as part of the World War I peace settlement. The Allies gave the Japanese a number of German U-boats. After the War, the Japanese Navy began to focus on the American Navy as its most likely future opponent. The Japanese began building an advanced submarine, the I-class submarines. This submarine reflected the empire that Japan began to conceive in Southeast Asia and the Pacific. The I-boats were very large submarines, reflecting the vast distances involved in Pacific operations. The I-class were 350 ft long and had ranges of 20,000 miles, more than twice that of 7,000-8,000 mile range of the German U-boats. The Japanese had smaller subs for coastal patrol, but the backbone of the fleet was the I-class boats. Surprisingly the substantial Japanese submarine fleet with the unique capabilities of its boats, had little impact on the Pacific campaign. Unlike the Americans, the Japanese began the War with the effective Type 93 Long-Lance Torpedo. The Japanese Navy never used their submarines to interdict American supply vessels. Rather they were used to target fighting ships with only limited success because of their tactical deployment. The Japanese used theor submarines as scouts and to targer warships. As the American offensive moved toward the Home Islands, the Japanese used their submarines to supply bypassed island garisons, some of which were near starvation. They were also used to supply bypassed islasnd bases where garrisons were close to starvation. They also managed to get some secret German military technology to Japan late in the war (1944). The Japanese developed especially large sunmarines that could carry a few planes. They were planning an attack on the Panama Canal until the subarines were redeployed to defend Okinawa (1945).

Early Submarines

The Japanese Navy got its first submarines from the United States, buying them from the Electric Boat Company in the early-20th century. Theseearly boats had very limited capabilities. We know of no significant use of these boats. More sophisticated submarines were obtained as part of the World War I peace settlement.

Inter-War Planning

Under the terms of the World War I Armistice, the Germans were required to turn ober all of their U-boats to the Allies. The German High Seas Fleet while including some excellent ships proved incapanle of challenging the British Royal Navy. The U-boats on the other hand, threatened the Royal Navy and Britain to the core. As a result, the British were determined that there were would be severe limits on the German fleet after the War. One of thoise limits was that the Germans would be prohibited to have submarines. Most of the German U-boats were scuttled. The Allies gave the Japanese, who had supported the Meitrranean naval campign, a number of the German U-boats. After the War, the Japanese Navy began to focus on the American Navy as its most likely future opponent. Here a najor bebefit was that both the Americans and British scuttled older vessels and restructed new vessel construction under the terms of the Washington Naval Treaties. This enabled the Japanese to close the gap in naval forces. The naval arms restrictions coverd battleships and crusiers. There were no limits on submarine construction. Japanese nationalists were incensed that Japan was not granted parity with Britain and America. In fact the limitations in naval construction enabled allowed the Japanese to close the naval gap. The Japanese did not have the capability of building much more ghan they actually built. The British and Americans actually had to scrap some of their battleships. In addition, both America and Britain had to build two ocean navies. The Japanese only needed a Pacific fleet. The Washington Naval Treaties despite their unpopularity within Imperial Navy circles were in fact ideal for the expansion of Japanese naval power relative to Britain and America.

Submarine Types

Japan began the Pacific war with a large, highly diverse submarine fleet. Their fleet included midget submarines, manned torpedoes (essentialy underwater Kamakazes), medium-range submarines, purpose-built supply submarines (which surprisinhly were used more by the Army than Navy), long-range fleet submarines, submarines with high submerged speed, and submarines that carried strike aircrft. Japan had the most diverse and highly capable submarine fleet of any World war II beligerant. Incredibly with all these special capabilities, the specialty boats used the most were the midget subs--the least capable. The Japanese began building an advanced submarine, the I-class submarines. They were the largest submarines of the War, in fact the lare submarines since the advnt of nuclear power. These submarine reflected the needs of the Empire that Japan began to conceive in Southeast Asia and the Pacific. The I-boats were very large submarines, reflecting the vast distances involved in Pacific operations. The I-class were 350 ft long and had ranges of 20,000 miles, more than twice that of 7,000-8,000 mile range of the German U-boats. These boats were capable of cruises lasting 100 days. The largest of the Japanese subs, the I-400 class was 390 ft long overall, they displaced 5,900 tons--better than twice the size of the standard Americn boat. The I-400 class could each carry three floatplane bombers, the only such submarines in history . Japan built 41 submarines that could carry one or more aircraft, while the vast submarine fleets of the United States, Britain, and Germany did mot have a sinle boat that could launch a plain. The Japanese had smaller subs for coastal patrol, but the backbone of the fleet was the I-class boats. Japan deployed a substantial submarine foce during the Pacific War. The Imperial Navy began the War with 63 ocean-going submarines. They added an additional 111 subs during the war. Out of that total of 174 boats, there were 128 boats lost -- an incredible loss rate.

Imperial Naval Doctrine

Japan saw their submarines as naval scouts. Their role was mostly to locate, shadow, and attack Allied naval vessels. This was a huge mistake. That said many U.S. Navy planners had the samne idea. The World War II submarine was greatly improved over World War I boats, but it was still vulnerable to surface attack and was very slow and had a limited field of vision, hardly ideal characteristics for scouts. Japanese submarines could sink warships and they did achieve some important successes early in the War against American carriers. They could not, however, hold their own against surface units--especially surface ships with the ASW capabilities being develoed in the BAttle of the Atlsntic. Where they were effective was in attacking slow, unarmed merchant men. The Imperial Navy did not, however, see that as an worthy target for their valiant warriors. A HBC reader writes, "The Japanese thought that attacking unarmed merchant ships was not a honorable thing to do. This is one of the reasons they never developed an offensive strategy like the Americans and also why the few captured American submariners they got their hands on were mostly tortured to death." This was a huge boon to the U.S. Pacific fleet which had to devote limited resources to protecting merchant vessels which would have diverted substantuakl resources on the huge distances in the vast Pacific. This was very different than the relatively short North Atlantic run. During World War II, the Japanese submarine fleet was cedited with sinking 184 merchant ships. Given the number of Allied merchant vessels, this was a very small number and had virtually no impact on the Pacific War. Overall, the Japanese submarine fleet performed badly compared to the American sunmarine force which virtually destroyed the Japanese maru fleet single handedly. Japanese garrisons were left to starve and war industries on the Home Island left without needed raw materials. Imperial Navy doctrine was an important part of the failure of their substantial submarine force.

Quality

The Japanese during World War II deployed some very effective, well engineered ships, notably their cruisers and destroyers. Japan's huge submarines, however, were an embarassment. The large ships were relatively easy to site visually and even more so with with radar and sonar. They proved slow in diving and hard to maneuver underwater. This left them easy to hit. In addition, the hulls were weakly built making them easy to sink. Also the Japanese had no radar until late in the War. The first radar sets were not installed on Japanese subs until very late (June 1944). And these sets were of poor quality. The lack of radar in the vast Pacific put the Japanese at a serious disadvantage.

Pearl Harbor (December 1941)

Part of Yamamoto's attack plan on Pearl Harbor included deploying 28 I-class submarines around the Hawaian Islands and Type-A midgit subs to actually enter the harbor. The idea was for the I-class submarine to attack any ships that managed to survive the air attack and exit the harbor. The air attack proved so effective that none of the battleships managed to get out of Pearl. The submarines, however, failed to intercept any of the critically important carriers that were not at Pearl during the air attack. Thus the submarine fleet played no real role. Actually the U.S. destroyer Ward spotted one of the midgit submarines and sank it which could have alerted Pearl's air defenses if the incident had been properly handled. In Japan, the midget subs were given great publicity and the crews treated with great honor--exceopt for the men who ran aground and surrendered.

Midway (June 1942)

Part of Yamamoto plan at Midway was for a screen of submarines to intercept the American naval force that would sally forth from Pearl Harbor once the Japanese fleet was sighted off Midway. The American carriers, however, were dispatched by Admiral Nimitz before the actual Japanese attack began. Nimitz had been alerted by code breakers. Thus they were in position north of Midway before the submarine screen had reached their positions between Pearl and Midway. The commander of the Japanese sub force negligent in getting his screen in place in the time frame ordered by Yamamoto. Thus the Japanese subs played only a minor role in arguably the most important battle of the Pacific War. One sub did sink the crippled carrier Yorktown. It had been badly damaged, but might have been saved. It was finally hit beyond repair by the Japanese I-168 sub.

The Solomons (August-December 1942)

The American attack at Guadacanal was the first Allied offensive in the Pacific. The naval campaign in the Solomon was one of the most bitterly fought of the War. Although the Japanese lost four of their first-line carriers at Midway, they still had a superior naval force. The Japanese deployed 15 I-class submarines to cut off the marines on Guadalcanal. They failed to do so through ineffective deployment and tactics. At the same time the Allied naval forces did prevent the Japanese on Guadanal from receiving adequate supplies. The Japanse submarine I-19 did suceeded in sinking the carrier Wasp (September 1942) and damaging the battleship North Carolina (September 1942). (This was done in one torpedo salvo which also sunk a destoyer.) This was a serious loss and a blow to the Pacific fleet, having already lost Lexington and Concord. Even so the American carriers had not only fought the vastly superior Japanese carrier force to a standstill, but severely weakened it. This bought the needed time for American shipyards to build new carriers and a host of other ships that would begin to arrive in substantial numbers by 1943.

Central Pacific (1943-44)

The American naval campaign in the Central Pacific brought new problems which further limited the operations of the Imperial Navy's submarine fleet. The Japanese occupied hundreds of islands in the south and central Pacific during its offensive following the Pearl Harbor attack. Supplying these island bastions proved a problem even before the American fleet had recovered. The growing Americans fleet cut off many island bastions. The submarines were the only ships tht could get through and were used to ferry supplies to these islands as they prepared for American assaults. But the Americans bypassed many of these islands. This became a major problem for the Japanese. Many islands were small and not capable of maintaining the large garisons that the Japanese crammed on them. Some submarines were used to ferry supplies to these islands. By the end of the War, some iof thgese garrisons were starving. The submarine of course is not an effective cargo vessel. It was an extremely ineffective use of these vessels. It not only blimited what coud be lanbded, but mean that the submarines were diverted from more effective action.

Usage

Naval historians fault the Jaopanese on their usage of the substantial submarine fleet. The Japanese Navy never used their submarines to interdict American supply vessels. The Pacific supply lines were long and vulnerable. Rather they were used to target fighting ships. Here they had only limited success because of their tactical deployment. The Japanese used theor submarines as scouts and to target warships. As the American offensive moved forward toward the Home Islands, the Japanese used their submarines to supply island garrisons that were targeted for invasion. They also used the subs to supply bypassed island garisons, some of which were near starvation by the end of the war. Not only were such operations wastefull given the limited cargo capcity of asubmarine, but operating in shallow waters around these islands exposed the submarines to attack. A sustained commerce campaign would have forced the Allies to divert resources and probably have delayed the Allied buildups. It is unclear why the Japanese did not launch a campaign against supply lanes. The Army's insistance 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.

Successes

While the Japanese submarines did not have a major impact on the Pacific War, they did have some important successes in the first year of the war that severely harmed the Pacific Fleets carrier force. The I-6 a monthafter the Peark Harbor attack put Saratoga out of action (January 1942). The I-168 delivered the final blows to USS Yorktown during the Battle of Midway (June 1942). The I-19 sank the carrier USS Wasp (September 1942) and damaged the battleship USS North Carolina (September 1942). This was at a critical point of the Pacific War. The Marines were clinging on to a narrow bridgehead on Guadalcanal. The Pacific fleet had very few carriers or battleships. This severely weakened the Navy's defense of the Marine bridgehead on Guadalcanal. Most of the important Japanese submarine actions took place during the first year of the Pacific War. The Americans and the British at the time were giving high priority on anti-submarine warfare (ASW), primarily because of the U-boat threat in the North Atlantic. As a result, the Japanese submarines through the rest of the War faced more robust American dfenses and had less success. As ASW developed, Japanese sub loses increased. Anti sub air patrols increased as the United States took more islands which by late-1943 gave them more airfields to work from using the long range Catalina flying boats and B-24 bombers. While the B-17 could carry a heavier load the B-24 was faster and had a longer range. Of less importance, although it has occasioned considerable, comment was the I-58 sinking the heavy cruiser USS Indianapolis after it had delivered the atomic bombs to Saipan (July 1945).

Radar

One key reason that the Japanese submarine force proved of only minor effectiveness in the Pacific War was the failure of the Japanese to develp and deploy radar. In the vastness of the Pacific, radar was absolutely critical. It was a major weakness of the Imperial Navy's surface fleet as well. The Germam's had sophisticated radar technology. It is unclear why it was not provided the Japanese early in the War. We know that a Japanese submarine reach Brest, France with a shipment of quinine (June 1943). They returned with German radar technology and technicians, but it was too late to develop and produce radars to equip the hard-pressed Imperial fleet. Transforming radar technology into actual production was a very complicated undertaking.

Axis Communication

Effective communication between the Axis partners was complicated when the Royal Navy instituted a naval blockade of NAZI Germany (September 1939). It at first did not completely end contact. Italy and Japan were still neutral and the Royal Navy was not as strong as in World War I. And the the fall of France meant that the NAZIs gained access to French Atlabtic ports which were easier to reach than German ports. Communication was completely severed when NAZI Germany attacked the Soviet Union (June 1941) and Japan attacked British and American Pacific bases (December 1941). This complicated Axis cooperative efforts. NAZI drives into the Soviet Union made possible long-range air contacts, but defeats before Moscow (December, 1941) and Stalingrad (November 1942) drove the NAZIs back. The only possible contacts possible became submarine exchanges. A Japanese submarine reached Brest (June 1943), but by this time Allied Anti-Submarine Warfare efforts were becoming increasingly effective. They also managed to get some secret German military technology to Japan late in the war (1944-45). The Japanese were attempting to get uranium oxide, but the German U-boat involved surrendered to the Allies after the NAZI capitulation (May 1945). It is unclear what the Uranium oxide was for, but the most likely possibility was a dirty bomb. As the Japanese had developed submarines capable of launching bombers, this could have been used to attack American Pacific-coast cities.

Air Attack Submarines

The Japanese developed especially large submarines that could carry a few small bombers. The I0400 class submarine was 400 ft long. It carried enough fuel fir 90 day voyages which brought the American west coast within range. The Imperial Navy was planning an attack on American cities, but the mission was changed to the Panama Canal. Closing the Canal would have greatly complicated naval operations and supply movement. The attack had to be cancelled when sufficent fuel could not be found, in large part because of the effectiveness of the American submarine campaign. The submarines in the final months of the War were redeployed to defend the Home Islands Japan from the expected Allied invasion.

Importance

Surprisingly the substantial Japanese submarine fleet had little impact on the Pacific campaign. Unlike the Americans, the Japanese began the War with the effective Type 93 Long-Lance Torpedo. The American submarine fleet played a major role in the War effort, essentially cutting Japan off from the resources it had seized in Southeast Asia. The Japanese had to station its fleet in Singapore rather than the Home Islands because of the fuel crisis. The population was near starvation by the end of the War. The very substantial Japanese submarine fleet had a very minor impact on the War. There are several reasons why the Japanese submarine fleet proved ineffective. One was it poorly used. The Japanese never developed an effective strategic role for their submarines. Two the Japanese Army coopted the submarines for use in supplying cut off island bases. Three the Japanese failed to develop and employ radar. Four, the Allied Anti-Submarine Warfare effort became ibcreasingly effective by 1943, improvements in both radar and sonar and new weapons like hedgehogs. The Allies destroyed 29 Japanese submarines in 1943 and 58 in 1944, effectively eviserating the Imperial Navy's submarine service.

Sources

Parish, Thomas. The Submarine: A History (Viking, 2004), 576p.

Created: 5:51 AM 6/21/2004
Last updated: 10:57 AM 8/13/2018