Japanese Submarine Campaign of World War II

At the outset of World War II the Empire of Japan was one of the major naval world powers with a powerful fleet of numerous aircraft carriers, battleships, cruisers and a very innovative force of submarines. In East Asian waters they had no equal and worldwide stood alongside the United States and the British Empire in having the most powerful fleets on earth. Japan possessed short, medium and long-range submarines, were not afraid to try to new things and had what was probably the best torpedo in the world at the start of the war. And yet, Japanese submarines failed to deliver results, falling far short of what they should have been able to achieve. Naval historians have studied this issue and almost invariably came to the same conclusion: Japan simply did not use their submarines effectively and thus they performed far below the awesome potential that the Japanese submarine fleet represented. In all, 190 Japanese submarines served in World War II and 129 were lost in action. In return, the Japanese subs sank 185 merchant ships and a little over 14 Allied warships. By comparison, the German submarine fleet sank over 2,500 merchant ships in the course of the war. The Italians (with fewer boats than Japan) sank 130 Allied merchant ships in the Atlantic and Mediterranean as well as 13 Allied warships. To illustrate the point another way, Allied submarines (mostly American) sank 19 Japanese submarines during the war while only one Japanese submarine ever sank an American submarine.

I-25, which bombed the continental United States

This does not mean that the Japanese submarine force was substandard; far from it. Japan showed immense ingenuity and innovative thinking in the design of their boats. It also does not mean that the threat posed by Japanese submarines to the Allies was negligible. Japan produced the largest submarine in the world during World War II as well as the submarine with the fastest submerged speed, even besting the famously high tech German Type XXI. Yet, both of these sub types came too late to ever see combat. There were Japanese submarine commanders who scored amazing victories, sinking major Allied warships and one, though it was not known until after the war, who launched the single most devastating attack in submarine history, sinking an aircraft carrier, a destroyer and badly damaging a battleship with one spread of torpedoes. Japanese subs had their weaknesses of course but also produced boats that were bigger or faster or able to dive deeper than anything the Allies had. The Japanese sailors certainly did not lack in courage, skill or training so, therefore, the only possible explanation for the disappointing results of the Japanese submarine fleet must be attributed almost entirely to how they were used. Japan had the tools and the talent but simply failed use these resources to their best advantage. Part of the problem was specific to the Japanese submarine force itself but it was also partly due to a broader failure in overall naval strategy.

With the experience of World War I, the Germans and Italians knew that the most effective way to use submarines was to focus primarily on the enemy merchant fleet and in this, as shown above, they performed extremely well. The Imperial Japanese Navy, on the other hand, was intent on using their submarines primarily against enemy warships and incorporated them into their plan for a climactic naval battle that would settle everything with one blow. This is often attributed to the great Japanese victory over the Russians at the Battle of Tsushima in which the entire Russian fleet was totally pulverized by the Japanese ships under the great Admiral Togo. Japan hoped to repeat this same success against the United States, unfortunately, the Americans refused to play by Japanese rules and that great clash of fleets, for which Japan had been saving her best ships, including the largest battleships in the world, never happened. The U.S. Navy fought at a distance mostly with airpower while most American battleships were only ever used to shell island fortifications. The United States also used its own submarines extensively against Japanese merchant vessels, effectively wiping out the entire Japanese merchant marine by the time it was all over. They too scored victories against Japanese warships, no greater success being the sinking of the Japanese super-carrier Shinano (largest warship in the world) by the American submarine USS Archerfish.

I-58, which sank the cruiser USS Indianapolis

This also reveals a lack of appreciation of the submarine in general by the Japanese naval high command. Just as Japanese submarines were not utilized to their fullest potential, Japan did not place sufficient focus on anti-submarine warfare and the American “silent service” made them pay dearly for the oversight. Other navies had tried the idea of surface ships and submarines working close together and invariably found the idea unworkable but when the big clash of fleets that Japanese naval strategists had planned for failed to materialize, no one came up with much of a substitute so that the Imperial Japanese Navy was left to simply react to whatever the U.S. Navy was doing at the time. Originally, the idea was to use submarines to scout for the surface fleet and to weaken the approaching enemy fleet where possible as the two sides came together. This accounts for the numerous Japanese submarines that were equipped with scout aircraft to increase their ability to spot the enemy fleet. However, such a confrontation never happened and so Japanese submarine strategy seemed to lose focus. What is frustrating for fans of the Japanese submarine force is that when Japanese subs were used to sink merchant ships, what most submarine experts at the time agreed was their greatest avenue of success, the Japanese boats performed very well, particularly in the less defended waters of the Indian Ocean. However, the naval high command repeatedly pulled them away for other duties.

Those “other duties” usually involved acting as cargo carriers themselves, taking supplies to beleaguered Japanese forces defending islands in the South Pacific. This is both understandable and tragic. It is understandable because the situation was desperate and any way to get any supplies to these forces in the face of American air and naval superiority over the combat zone had to be looked at. The suffering that Japanese soldiers and sailors on these islands, especially Guadalcanal, was so immense as to defy description. Wracked by starvation, exhaustion and tropical diseases, as long as the poor soldiers were not evacuated, it is understandable that any means of getting supplies to them had to be considered. However, it is tragic because they simply should have been evacuated at that point as submarines are simply not effective cargo vessels. They amount of supplies they could possibly carry would necessarily be quite small and this prevented the subs from doing their real job which was sinking enemy ships, a job they were quite good at when given the chance. Subs were also detailed to undertake operations such as shelling the U.S. coast or dropping incendiary bombs in the hopes of sparking massive forest fires which, even if successful, would not have had any major impact on the war and, again, diverted them away from what they were best suited for.

I-53

When it came to combat operations, the Japanese submarine fleet had weaknesses as well as strengths. Japan, like the other Axis powers overall, lagged behind the Allies in sonar and radar technology. Radar sets were not adapted for Japanese subs until 1944 and even then were of very poor quality which, combined with the fact that Japanese subs were necessarily large (due to the fact that they had to have a long range to fight effectively in the massive Pacific) and thus slow to dive meant that being caught on the surface, particularly by Allied aircraft, was a real danger. Likewise, Japan possessed only rudimentary passive sonar which was not as effective as that used by the Americans which, combined with the fact that Japanese submarines tended to make more noise and be less maneuverable (due to their size) put them at a disadvantage when it came to underwater operations. However, Japanese submarines also had advantages over their Allied counterparts at least for a period of time and, unfortunately for Japan, the most innovative sub types were not completed until the war had already been lost and never saw action before Japan surrendered in 1945.

At the outset of the war the biggest advantage Japanese submarines possessed was the Type 95 torpedo which had a very long range (up to 13,100 yards), packed a powerful punch and which ran on oxygen rather than compressed air which meant that it left no tell-tale trail of bubbles behind it, making it much harder to spot by surface ships before it was too late. In comparison, at the beginning of the war, the standard American torpedo was a complete disaster that frequently failed to hit its target, often failed to detonate when it did and sometimes posed a greater threat to the boat that fired it rather than the enemy. The Japanese naval technicians were also constantly working to improve their boats. The Kaidai 6 a/b type, produced in 1934-38, had the fastest surface speed of any sub in the world at 23 knots. The AM Type boats were built to carry attack aircraft and supplement the famous SenToku class boats and had the potential to be quite effective. However, only four were ordered and only two were actually completed before the high command ordered production halted to focus on smaller subs for the defense of Japan.

The gigantic SenToku-class submarine aircraft carrier

This highlights another problem of the Japanese submarine fleet which relates back to the overall problem of a lack of focus. In production as well, Japan produced a wide variety of sub types which was expensive and time consuming while never producing very many of any one type so that even the most effective boats were too few to have much of an impact. Other navies, most especially the Germans with the medium-sized Type VII, settled on one type of submarine that best fit their needs and then produced as many of them as possible. For Japan, where resources for construction were scarce, producing so many different types of submarines with orders often being cancelled before construction was complete to switch work to another type proved to be wasteful of both resources and time which, especially as the war progressed, Japan had very little of to spare. Probably the most innovative sub type Japan built during the war, the SenToku class, is an example of this. The great Admiral Yamamoto, a far-sighted commander by any standard, supported this type of submarine with enthusiasm. However, after his death, the project was put on the shelf and work was not taken up again until later in the war so that, as we know, by the time the I-400, I-401 and I-402 were put into service, none had a chance to see action.

Certainly there are two types of submarines produced by Japan which most illustrate the great potential that the Imperial Japanese Navy had for submarine warfare if only it had been properly utilized. The first is the most well known, the aforementioned SenToku class which was the largest submarine type ever built and would retain that status all the way until 1965 with the launching of the U.S. nuclear ballistic missile submarine USS Benjamin Franklin. These were huge boats built to be, essentially, submarine aircraft carriers to launch surprise air attacks on extremely distant targets that would never be expected. Their design was highly innovative and a brilliant example of the creativity of Japanese naval engineers. Each could carry two small Seiran bomber aircraft as well as sufficient parts to be used to either repair the other two or put together for a third plane. The subs were coated with a special material, passed along from Germany, to make them more resistant to underwater search gear, special equipment was developed to allow for the aircraft to be prepared for flight while the boat was still submerged so that the boat could surface, launch its aircraft and submerge again as quickly as possible to avoid detection. These boats also had the longest range of any submarine ever developed and would hold that record until the development of the first nuclear submarines by the United States. Even today, there has never been a conventional submarine with a longer range than the Japanese SenToku class.

The 'super sub' I-401

Their great range was critical as the original intention for these boats was to cross the Pacific Ocean, hopefully undetected, rounding Cape Horn, crossing the Atlantic Ocean to then launch what would essentially be terror-raids on urban targets such as Washington DC or New York City. Everyone realized that the actual damage they could inflict would be rather limited, however, the intention was to spread terror among the American populace by attacking the United States where they least expected it and where they seemed most invulnerable. It could have had a considerable impact, forcing the American military to redeploy resources to defend against attacks on areas they never would have thought to be within reach of the enemy. That was the real aim of the I-400 boats, it was a way to send a message to the Americans that Japan could hit them almost anywhere, that no coastal region was safe. However, as we know, by the time the boats were launched the situation had changed and so when finally put to sea for their first, incomplete, war cruise, their target was instead to be the locks on the Panama Canal, the destruction of which would cripple shipping in the area, make Central America a virtual ‘dead zone’ and force all ships to sail the long way around Cape Horn at the bottom of South America. The war ended before this attack could be carried out but the potential represented by the SenToku class boats was lost on no one and one of the early American guided missile submarine designs seems likely to have been based on the I-400.

The other class of submarine produced by Japan, which highlights Japanese submarine innovation and unrealized potential is less well known but deserves to be celebrated. This was the SenTaka class of which three boats were completed before the end of the war, I-201, I-202 and I-203. In terms of their design, these boats were years ahead of their time and were precursors of the design changes in submarine hulls that would most come to be associated with the age of nuclear submarines. These boats had anything that could cause drag either removed or made retractable so that they were extremely streamlined, making them much faster and more maneuverable underwater than anything the Allies had. The electric motors were twice as powerful as the diesel engines and they were equipped with high-capacity batteries that allowed for huge bursts of speed so that these boats were capable of achieving speeds of over 21 knots while submerged, something unheard of at the time. No other submarine in the world could go so fast underwater as the SenTaka class and they were also fitted with a snorkel so that they could recharge their batteries without having to surface. As a result, though they were small boats with a rather short range, they could conceivably have operated entirely submerged for the duration of their patrol which would have made them almost impossible to detect until they started sinking Allied ships. With four forward tubs and ten torpedoes with two deck guns they also packed a respectable punch for such a small boat.

The highly advanced HA-201

The I-400’s may get the most attention for being so big and scary but the I-200’s actually represent an even greater potential of Japanese submarine success. With the underwater speed and underwater endurance these boats were capable of, they would have been extremely difficult to locate and destroy. If they had been completed earlier in the war and in larger numbers they could have taken a devastating toll on Allied shipping, perhaps even playing a decisive part in the Pacific War. These little boats would have changed almost all the rules that the Allied navies were playing by and could have had a tremendous impact, possibly even affecting the outcome of the war. Who can say? However, as it happened, only three were produced before it was all over. I-201 and I-203 were taken to Pearl Harbor after the surrender where I-201 was sunk in an ordinance test and I-203 was sunk as a test target (though we can be sure the U.S. Navy studied them intensely before doing so). The I-202 was damaged in an air raid from an offshore U.S. aircraft carrier while in port and later scuttled off the Japanese coast in 1946. None saw combat but these boats perfectly illustrate the immense creativity and potential the Japanese submarine force was capable of but never fully utilized.

Finally, if all of this seems rather depressing for submarine enthusiasts, we have to keep a few things in mind. For one, the submarine force was not alone in being robbed of the chance to achieve its greatest glory. Japan famously produced the largest battleships in the world, saved for the hoped for decisive fleet battle with the United States, and none were ever able to really show what they could do in a ship-to-ship shooting match before they were sunk. It should probably also be mentioned that, like the Americans, the Japanese had little to no submarine combat experience before World War II. That does make a difference as we can clearly see what the German U-boats were able to achieve under the command of Admiral Karl Doenitz who was a veteran submarine commander who saw action in World War I as captain of UB-68. Even for the United States, while lacking the combat experience that the Germans had from World War I, it made a difference that the American naval commander in the Pacific was Admiral Chester Nimitz who, as a young officer, had commanded the USS Skipjack and held numerous submarine flotilla commands prior to World War II. He may have lacked combat experience but he certainly knew and appreciated what submarines were capable of and used them to best effect.

I-58 carrying Kaiten 'human torpedoes'

The results achieved by the submarines of the Imperial Japanese Navy are, ultimately, deemed unsatisfactory in large part because anyone can see that they had so much potential. It is not that they had no victories but that they were capable of having much, much more extensive victories if only they had been properly utilized. It should not be forgotten then that the toll taken by Japanese submarines during the war, over 900,000 GRT (gross register tons) of Allied merchant shipping, was a loss that was certainly felt by the Allies. Japanese submarines sank ten small warships, two cruisers and two American aircraft carriers during the course of the war. Let that fact sink in for a moment. That was more than anyone else has done against the U.S. Navy. The problem was simply that the Japanese naval high command refused to change their thinking when their original strategy proved unworkable. They lacked focus, building massive submarines that never saw service and tiny, suicide weapons, the famous “kaiten” which ultimately did very little damage to the enemy, rather than mass-producing a greater number of one or two submarine types such as the Germans did with the Type VII and Type IX or as the U.S. did with the Gato, Balao and Tench-classes. Japan had the largest, the smallest, the fastest, the deepest diving submarines and Japan made the most destructive single submarine attack in history. However, the lack of adaptability, technological deficiencies and a lack of focus by the high command prevented the Japanese submarine force from accomplishing much more, even, on perhaps more than one occasion, being a decisive weapon in the Pacific War.