The submarines of the Japanese Navy consisted of some of the most capable in the world at the beginning of World War II. All the submarines built from the outset for operations in the war significantly outranged the submarines of the Allies navies. The range advantage provided the ability to operate at extreme distance from home port or maintain a long on-station time in a given area. Subsequently, the Japanese were able to apply their influence further and longer than other submarine forces. Along with the superior operational reach of the submarines, excellent torpedoes were provided that had a long range and powerful warheads.
The Japanese technological advantage did not wane during the course of the war. It diverged to three different branches: large, small, and fast. The Japanese used their skill to build the largest submarines in the world (Sen Toku Type) as well as some of the most capable small submarines (kaiten and other midgets). Most impressive of all of their designs, however, is the Sen Taka Sho Type medium attack submarine that had an acceptable cruising range coupled with outstanding underwater speed. Had more of these submarines reached operational status earlier, the American forces would have had a unique foe on their hands.
Even with the technological advantages of their designs, the Japanese submarines did suffer from a lack of resources that placed limits on the number of submarines that could be built and on the timeliness of the build process. Also, the Japanese did have a significant delay in developing and installing radar on their submarines. While it was a deficiency, it would not have had significant influence if the focus on operational security had been stronger.
The training of Japanese submarine crews was without equal. The submarines spent long periods of time out at sea constantly practicing elements of the plan for a decisive battle. The intense training periods had such a level of realism that three submarines were lost in prewar training accidents. The training was not without fault however. The overarching focus on the submarine role in the “decisive battle” limited the growth of submarine force capabilities. The overall training gave minimal consideration to key aspects of submarine operations: surveillance, commerce raiding, and sea control (area denial).
Based on the mystique of the German Submarine Force and the results of the American Submarine Force, it would be easy to jump to the idea that had the Japanese Submarine Force strictly applied a strategy of commerce raiding it would have had a greater impact on the war in the Pacific. This argument is too simplistic and discounts the enemy that each respective country was targeting. Japan and Britain, as targets of America and Germany respectively, were island countries dependent on long lines of communication for necessary resources and forces to fight the war. These lines were vulnerable to the focus of intense submarine efforts. Both America (in the Pacific) and Germany were also faced with the lack of a strong surface fleet to conduct offensive operations. The Germans were held in port by a combination of factors, and the American Pacific Fleet was attempting to rebuild after Pearl Harbor. As such, commerce raiding against fragile lines of communication was their only recourse.
The Japanese faced a far different situation at the outset of the war. They had built a large fleet focused on a single strategy. They had a single opponent to be concerned with and that same opponent did not have the immediate ability to attack their nation. The Pacific Ocean provided a strategic safety buffer from American forces. The surprise attack on Pearl Harbor reduced the effective combat power of the American Fleet and put them immediately in a defensive posture. The American Navy was not altogether prepared to face the Japanese and an early focus on commerce raiding would have not been able to have an influence similar to that which the American submarines achieved. The Japanese, for all of their superiority in submarine technology, would not have been able to influence the American East Coast. While forces could be moved to act against the West Coast, the force size was too small to carry out effective operations to limit commerce or other operations on the East Coast. Further, there was no method to influence the natural resources available in America proper.
While the focus on a single decisive battle that was unattainable was short-sighted, the understanding that the Japanese Navy needed to focus on American military strength was not improper. The submarine force, as well as the rest of the Navy, was constructed for naval engagement not commerce raiding. The true failure of the force was not to focus its efforts on the opportunities that presented themselves. Pearl Harbor, Midway and Guadalcanal all presented themselves as opportunities for potentially decisive actions. In all three actions, the number of American aircraft carriers available in the Pacific was limited and the ability of the American Navy to conduct continued combat operations was at risk. The Japanese submarine force, based on direction from the Navy Staff, scattered its units to various other theaters away from the major battles, mainly the Aleutians and Indian Ocean.
Had the Japanese submarine force maintained the full cordon around Pearl Harbor after the 7 December attack, they could have effectively maintained ten or more submarines on station continuously when based out of Kwajalein. The size of the Japanese submarine force (capitalizing on significant operational range of the large designs) could have significantly slowed the resupply and rebuilding of Pearl Harbor and denied the American Navy its last key strategic outpost in the Pacific forcing them to extend their lines of communication and operation for any effort against the Japanese a few thousand more miles all the way back to the American West Coast. American operations from the West Coast would have been more vulnerable to the Japanese fleet.
An effective blockade of Pearl Harbor had the potential to expose it to an amphibious invasion which would have further challenged the American ability to recover from the initial attacks and generate offensive initiative.
Had the Japanese submarine force applied the principles of mass and unity of effort to their employment of forces at Midway and Guadalcanal, the operational submarine units in the areas of these battles would have been tripled posing a far greater risk to the American forces. The larger number of units at Midway would have increased the opportunity of early detection of American forces, specifically the aircraft carriers, potentially allowing the Japanese carriers to focus their effort against the American task forces prior to attacking Midway proper. This employment would have more closely met the training that the submarine force underwent during the interwar period potentially raising effectiveness as well.
The Japanese submarine force continued to deny the principle of mass in operations during the American invasion of Guadalcanal. Submarines were still deployed to various marginally important areas rather than the area of Guadalcanal. The small number of submarines assigned to the Guadalcanal area was further diverted from the potential decisive battle by being tasked to conduct supply operations instead of attempting to thwart the invasion and buildup. The respect shown by the American forces for the submarine threat could have been taken advantage of by a larger effort focused on them. Instead, the opportunity to stall the American advance in the South Pacific was given little direct attention while effort was applied to meaningless supply operations and Aleutian and Indian Ocean excursions.
Even as the opportunity for the handful of critical battles passed and the Japanese were placed firmly on the defensive, proper employment of the submarines could have still brought considerable results. The Japanese submarine force consistently showed the ability to complete complicated approaches and attack challenging targets. The sinking of Yorktown at Midway and Wasp at Guadalcanal are proof that the prewar training and exercise experience developed a skilled force that could find success in operations against a determined opponent. Had the Japanese focused their effort against the American offensive, the submarine force had the ability to influence operations. Unfortunate choices to hinder the submarines’ tactical freedom limited their influence as the Americans advanced through the Central and Western Pacific.
The final, and most perplexing, failure of the Japanese submarine force was its inability to learn and adapt to the conduct of the war. From Pearl Harbor through the operations in the Marianas in 1944, Japanese submarines were employed in rigid scouting lines and consistently failed to intercept and report on American fleet movements. Not until the force had suffered the loss of even more submarines in the Marianas did the staff shift their employment to patrol areas where the boats would be able to more freely search for targets. That late in the war, the shift was meaningless. Because the force was so decimated, there were not sufficient boats available to mount a solid defense of the Philippines. The employment of scouting lines failed in every instance that it had been used. The lines were not maintained intact around Pearl Harbor to maintain the cordon.
They were late to take station and then moved without an overriding plan or effect at Midway. They were haphazardly strung around the Solomons, Gilberts, Marshalls and Marianas and shifted without operational thought. Only late in the war were submarines released to freely stalk for prey. At this point the force size was too small to have any influence. Submarines were regularly removed from offensive or defensive operations to support grandiose airborne reconnaissance or nuisance strike missions. Submarines were committed en masse to both K Operations as well as reconnaissance and strike flights over Ulithi. The bombings had little effect. The support of reconnaissance missions, by acting as refueling platforms or navigational aids, discounted the ability of the submarines to do the jobs themselves. The submarine force had provided the first photographic intelligence of the results of Pearl Harbor as well as prescient intelligence of preparations at Midway, but the opportunity for later use of submarines as the primary operator in this key role was ignored.
The Japanese submarine force was undoubtedly a technologically superior force at the outset of the war. They were highly trained and well organized to support a distinct form of battle. The training and experience gained in interwar exercises provided a force that was ready to directly face the American Navy. The planning and execution of the war strategy failed to capitalize on the specific skill set of the submarines that were available. Had the submarines been employed as anything more than an adjunct force supporting other efforts, they could have exerted a strong influence and produced costly losses for the American Navy opening the Pacific to further Japanese operations.
The Japanese submarine force was uniquely prepared for operations against enemy combatants and did not need to resort to commerce raiding to have an influence. In fact the early successes of the Japanese Navy made commerce raiding unnecessary. Unfortunately, the Japanese did not capitalize on early successes by maintaining their forces forward and massed for further strikes against American forces. Once the paradigm of the Pacific War changed to a protracted conflict with American forces operating on extended lines of communication, the Japanese failed to adjust their employment strategy and shift to concerted commerce raiding efforts. The failure to learn from the experiences of the German and American submarines as the face of war changed left the Japanese unprepared to have any influence as the war came to an end.
Properly employed, the Japanese submarine force could have been the key to a very different war. Instead, their misemployment only aided in allowing the quick rebuilding of American forces due to their industrial dominance. As such, the actions of Japanese submarines only became footnotes to most major naval battles in the Pacific Ocean.