What did the Japanese Navy plan to do in a Pacific war? How did they plan to win it? Well, it was all quite simple really.
Hello everyone and welcome to History of the Second World War Members Episode 7 - How to Win a War, Maybe. Over the previous episodes we have discussed the Japanese navy, and some of the technical aspects of it ships. During this episode we will look at how the Japanese planned to use those ships in a confrontation with an enemy fleet. The Naval Arms Limitation treaties put certain restrictions on what the Japanese could plan to do during such a conflict, for example, the Japanese Navy would always be at a numerical disadvantage when it came to capital ships. This was a known fact that therefore a good amount of Japanese planning was focused on trying to make up for these shortcomings through the use of qualitative superiority and skill, which would offset their quantitative disadvantage. They invested heavily into tactics that they believed would neutralize the advantage of their enemies, like night fighting which we will discuss later in this episode. There would be some mistakes made by the naval leadership, and in some ways they were very similar to the mistakes being made by their enemies. For example in their planning both the Royal Navy and the American Navy often tinged their evaluations of the Japanese with no small amount of racism, just a general belief that their men and their ships were simply superior to what the Japanese were working with, and if they came to blows it would prove to be the difference. This gave both navies an unearned feeling of superiority which they would pay for when the war began. On the Japanese side there was a similar but opposite belief, and this was that that the Japanese sailors had a superior fighting spirt, and that this moral superiority would in some way offset any other disadvantage, this would also cause issues for the Japanese navy during the war. These problems aside, there were constraints placed upon the Japanese Navy based on the strategic and economy reality of Japan’s position. By the First World War Japan was heavily dependent on imports to provide for its citizens, its economy, and most importantly the military. These imports ranged from food to oil and everything in between. For the Imperial navy this meant that if it wanted to participate in a war it had to find and secure sources of oil, rubber, and various minerals. In a conflict with any other nation it would be critical for the Japanese war effort that these supplies be not just secured, but also the safety of the transport system was guaranteed. As the United States shifted into focus as the most likely enemy for Japan this became even more critical due to the reliance that Japan had on the United States for many imports, especially oil. In 1936 the Navy would create three committees to formulate Japanese naval policy and plan its actions for a conflict. The First Committee would be in charge of creating plans for a southward expansion, which is where these resources could be obtained. While securing resources was seen as important, the Navy believed that to secure those supplies it would be necessary to meet the enemy fleet in combat, and that would take place in one large decisive battle at sea. The idealized version of this battle was a lot like Jutland, and unlike Jutland it would be decisive. Trying to find a way to induce this type of battle, and to provide a Japanese fleet with the greatest chance of winning it, would dominate Japanese naval planning between the wars. The Japanese would never really be shaken from their search for the decisive fleet engagement, but they realized that the war might be long, and if that was the case then access to resources was paramount, even before the destruction of the enemy fleet, which meant whatever happened the Navy would have to plan for both that fleet battle, but provide enough resources for a secure southward expansion.
As with all of the navies of the world the Japanese navy had its fair share of problems related to finding the right people to lead in the formation of future war plans. One of the the problems that would later be blamed for some of the Japanese failures was a lack of original thinking among many of its top naval officers. Rear Admiral Nakazawa Tasuku, head of the Operations Section from 1939 to 1940 would say after the war that “Japan lost the war because the navy was dominated by the top graduates of the Navy Staff College who blindly followed its instructions and were void of originality.” The Navy’s personnel policies often caused problems as it featured a king of semi-automatic promotion which meant that at times far less capable officers were promoted simply due to seniority. There was also a trend of removing certain officers based on their political and strategic views. So for example, many of the officers who had supported the Naval treaties, and believed that they were actually good for Japan, were removed after 1933. This shifted Japanese thinking, and was one of the reasons that the Japanese navy was dominated by the view that a war with the United States was inevitable. It had the side effect of restricting the ability of the Navy to completely rethink their plans during the 1930s. Even though there were many technological breakthroughs during the period, the basic foundations of Japanese naval policy did not change much from its roots after the First World War. This inability to reconsider the path of the navy at a more foundational level caused construction, maneuvers, new officer education, and planning to all be done along one line. In Mahan to Pearl Harbor: The Imperial Japanese Navy and the United States Sadao Asada would say “The fixation with the decisive battle blinded the conservative majority of Japanese officers to the extent to which technological innovations, especially in air power, had transformed conventional warfare.”
In the Imperial Defense Policy of 1923 the United States was elevated to be the primary threat in a future conflict, and this meant that a conflict with the United States would occupy most of Japanese planning resources. The belief that a conflict with the Americans was not just likely but inevitable and unavoidable would grow during the 1920s. If the Japanese wanted to come out of such a conflict victorious it was important that they understand the possible courses of action available to the Americans in a war. It was generally understood that the Americans would have to move west across the Pacific to defend their territory in the Philippines, and to take it back from the Japanese if it had been captured. To make this trans-Pacific move there were four possible routes that could be taken. The shortest was in the north, from Pearl Harbor then up to Alaska, down through the Aleutian islands, and then to Japan. While this represented the shortest and fastest possible route, the weather at those latitudes would prove to be a serious problem and so it was not considered to be a real threat. On the opposite side was the southern route, which would have allowed the Americans to safely move from one British and French base to another across the southern pacific. This was also considered to be unlikely because it would require quite a bit more time as it was the longest route. In between these two extremes were two central routes, which were seen as the most likely. Both of these routes would begin at Pearl Harbor, with one then moving between the Bonin and Mariana Islands and the other further south through the Gilberts, Marshalls, Truk, and Guam. Both of these paths were seen as very likely, and which would be chosen seemed to largely depend on the specifics of the American plans. However, it was believed that the southern course through the Gilberts and Marshalls would probably be more likely. These assumptions made by the Japanese were really quite good, and were very much in line with American planning during the 1920s. Over in the American Navy there was a lot of debate about how to persecute a war in the Pacific, and specifically how aggressive the American Fleet should be in its journey into the Western Pacific to prevent an attack or to relieve a siege of the Philippines. During this push west, regardless of the exact route, the Japanese planned to execute attritional attacks on the American fleet. We discussed last episode how this part of the plan altered the design of some of the smaller Japanese ships, with destroyers, cruisers, and submarines all being designed to fill a role in this attritional strategy through the use of torpedo attacks. These attack would be such a key part of the Imperial Defense Policy that after 1923 they would be frequently under the name “zengen sakusen” which more directly translates into “progression reduction operations.” These actions were not seen as the end goal of the campaign, but simply a precursor to the expected final battle. They would be launched as soon as the exact location and course of the enemy was determined. The Japanese also believed that the American fleet would not sail immediately at the start of the conflict, instead they would wait while their fleet gathered and prepared for the long Pacific journey. This would provide the Japanese with the time to launch some ancillary operations in conjunction with the army. The most important target was the Philippines, which was known to be an important American air and naval base and the most likely final destination of the American fleet. The Japanese military would launch an attack on Luzon with the goal of capturing Manila and eliminating the American military forces on the island. Then other operations would be launched to secure key natural resources. The goal would be to have these attacks completed before the American battlefleet started across the Pacific, and in fact one of the key benefits of the attacks is that it was believed that it would force the American fleet to make the aggressive move across the Pacific, falling right into Japanese plans. All of these assumptions are of course ripe with possible avenues for criticism as we look back on them today. The major problem with how the Japanese estimated what the Americans would do was down to the fact that they assumed that the Americans would not react in a major way to what the Japanese were trying to do. They believed that the Americans would almost blindly charge across the Pacific, ignoring the fact that it was exactly what the Japanese were hoping for. It also seems that the plans were based around the concept that the Americans would have no idea what the Japanese were doing, and would not know until the last moment the position or disposition of the Japanese fleet. In reality the American plans called for very advanced fleet scouts and the use of aircraft that would work incredibly hard to determine the position and make up of the Japanese fleet, and as aircraft became more and more capable the ability of the Americans to gather more intelligence continued to improve.
Under the assumption that the American fleet would move west, the Japanese fleet planned to meet it and defeat it, and this was the second stage of the Japanese plan, and also one that would undergo many revisions over the interwar years. Beyond the general outline of the Japanese fleet meeting the American fleet in a gun duel many of the basic assumption of the battle would be revisited several times. The basic outline was that Japanese light forces would attack the American fleet in the night leading up to the battle. The battlecruisers would seek out and destroy as much of the enemy screening force as possible, which would allow the smaller ships to close in for their torpedo attacks. This would weaken the American fleet, and was expected to disable up to ten American capital ships, along with a large number of smaller vessels. This would then cause confusion among those smaller American ships and hopefully throw the entire American fleet into at least some level of disarray. All of these actions up to this point would be in service to putting the Japanese battleships into the best possible scenario for their actions the next day, with the Battle instructions published in 1934 stating “The battleship divisions are the main weapon in a fleet battle and their task is to engage the main force of the enemy.” This would allow the Japanese capital ships to close to within 22,000 meters, which was thought to be the optimal range for an engagement. It would be during this firing that the decisive moment would come. One criticism that could be levelled against these plans was their complexity. I have stripped out much of the complexity and details, but in the official Japanese plans there were incredibly specific details about which squadrons should be in which place and engaging the enemy at what time and then where they should move after. This was not a Japanese specific problem, but the Japanese plans were at times much more detailed and complex than those found in other navies. One basic assumption that would be revisited over time was the time of day in which this battle would take place. During the 1920s it was generally assumed that the battle would have to take place during the day, probably early in the morning. One of the changes considered during the 1920s was that instead of a daytime battle there would be the possibility of launching the main attack either at night or late in the evening. Another piece of the puzzle that would shift over the years was the expected location of the battle. In general over the course of the 1930s the expected point of the confrontation moved further and further east. Advances in naval technology also forced alterations to these plans, with engagement ranges continuing to increase and of course the growing capabilities of aircraft. As the range of aircraft increased over the course of the 1930s the ability of the fleet to move without being found by enemy planes became more and more unlikely. This made Japanese interception strategies more difficult, because if the Americans were more likely to know where the Japanese was far in advance it was far more likely to react to the Japanese attacks, or to simply opt out of combat and sail away if it felt that it was at a disadvantage. The growing power of aircraft also provided advantages to the Japanese though, with it becoming a greater and greater possibility that Japanese air strikes could provide a valuable boost to those attritional operations that were so critical to Japanese strategy.
Even with the changes in technology the Japanese naval designs still focused as good portion of their energies on the surface engagement. This focus would be the root of the superbattleship strategy that would result in the Yamato and Musashi. This was part of the continued emphasis on achieving a qualitative superiority for the Japanese Navy, and from the beginning these ships were planned to be the largest and most powerful surface combatants in the world. The size of the ships was also targeted specifically at the American Navy. When it came to ship size the American navy was under the serious constraint of how large their vessels could be and still transit through the Panama canal. To maintain their strategic mobility between the Atlantic and Pacific it was incredibly useful for ships to fit through the canal and so the Japanese believed that the Americans would be hesitant to build ships that were too large. Even if the American ships were built as large as those of the Japanese it was hoped that through great secrecy they would still maintain a lead of several years, which would provide more than enough time for the war. This is why the development of the 18 inch guns for these new battleships was done in such secrecy. The original plan was to mount 20 inch guns, but these were downsized to 18 inches in the official plans that were put in place in August 1934. During 1933 the Kure Naval Arsenal had already begun testing the new guns, although they were officially reported to be 16 inch guns and could not be mounted on capital ships due to the constraints in the naval treaties. The final requirements for the ships were that they would mount the new guns, be able to fire them up to 30,000 meters, have a maximum speed of 30 knots, and a range of 8,000 miles at optimal cruising speed. By late 1935 there had been many designs and plans for the new ships, which were continually refined until March 1937 when the final design was approved. These plans, and the four planned superbattleships were the zenith of prewar surface combat power, and the Japanese believed that it would give them a decisive advantage in the expected climactic surface action.
With the focus on setting up for the fleet battle, there were changes forced upon the planning in the years before the war in the late 1930s. As I mentioned earlier the planned decisive theater was pushed eastward until in 1940 it was felt that it would occur as far east as the Marshall Islands. This eastward push was justified by the continuing increase in aircraft range, which required the Japanese fleet to keep the Americans further away from the home islands and the critical supply lines running south. Naval air units also began to take on a critical role in maintaining complete air superiority while the fleets were in action. Even at this very early stage the Japanese leaders recognized that such efforts could be costly, but if it was all in service of guaranteeing the success of the battleships any sacrifice was considered to be worthwhile. This included everything up to and including one way strikes that sacrificed aircraft, or even sacrificed carriers, as long as the American carriers were also neutralized. If the American carriers could be destroyed, even if it cost all of the Japanese air assets, it was felt that it would be to the advantage of the overall Japanese plan. Aerial reconnaissance of the American movements was also planned for, and to that purpose the Fourth Fleet would be organized with the purpose of reconnaissance and also strikes against any islands that the Americans tried to use as forward operating bases.
There would be two constants throughout all of these plans and alterations, the first was of course the supremacy of the battleships, but the second was the importance of the night operations that would precede it. The biggest change to these night operations during the 1920s and 1930s was simply that they were considered to be more important, and they were provided with more resources to give them more impact. During the 1920s the plan was to use night attacks by smaller ships to put some attrition on the American ships, but they were seen as wholly subsidiary to the decisive battle, a kind of disconnected prelude. In the 1930s they started to take on a greater focus as the situation changed. The first problem was that the United States began to drastically increase the number of heavy cruisers it was constructing, which were required greater strength be given to the Japanese night attack forces. The second development was that the Japanese navy increased its ability to detect and engage ships at night due to the presence of new and improved optical equipment. This was still before radar came into play, and so having better visual equipment allowed the Japanese to detect enemy ships at greater range which gave their night attacks a better chance of success and a greater opportunity to inflict serious damage. The realization that greater results might be possible caused ships as large as the Kongo class battlecruisers to be included in the night fighting squadrons, although smaller cruisers and destroyers would always make up the bulk of these formation. This shift would reach its height in 1934 when the Battle Instructions for that year called for the decisive fleet engagement to occur late in the evening, then through the night, and then to be finished the next morning. The next years instructions would revert this radical change back to a more orthodox daylight battle, but even the fact that the Japanese were considering large night operations is interesting. To try and provide some structure to these night attacks the Yasen Butai was formed, which would incorporate all of the night combat groups that were with the fleet. These groups would be detached from their normal squadrons when the time was right and they would be formed into the Night Battle Force which would attack the enemy fleet, push through the outer ships, and unleash as many torpedoes as possible at the main force of enemy capital ships. This would remain the plan for night fighting until the beginning of the war.
Up until close to the start of the war the Japanese war plan was as described above, however with the start of the war in Europe, and how well it was going for Germany, caused the Japanese navy to reconsider a few of the assumptions that it had made along the way. With so many nations in Europe having been conquered by Germany by late 1940 it seemed that some of their Asian colonies were much more vulnerable that originally thought. This caused many within the Navy to begin advocating for a more aggressive approach to expansion in southeast Asia. In 1940 the Americans would also move their primary fleet base to Pearl harbor and in July of that year the Americans announced a new two ocean navy plan which would massively expand the American naval construction program. This expansion meant that the Japanese capital ship ratio, which would be at or very close to 780% in 1941 would begin to rapidly decrease in future years. The United States was planning to build three times as many ships as the Japanese were, thanks mostly to the massive scale of American industry. This change threw the Japanese naval leader for a loop. The plan had been based on the idea that the American industrial capacity would not start coming into play until after the war had already started. This would allow the Japanese to be at their best possible position at the start of the war, and then if they could force a major fleet encounter they could have relatively even strength with the Americans. But with this new building program, if the Japanese waited even a few years they would be at such a disadvantage that it would approach the point of impossibility. This would play an important part in propelling the Japanese Navy into supporting the start of the war in 1941. When Admrial Nagano Osami became Chief of the Naval General Staff in April 1941 he brought with him the view that war was inevitable, and it was clear that the longer that the Japanese waited the worse position they would be in. These feelings would continue throughout the summer, and then in August Roosevelt would freeze Japanese assets in the United States which put a de factor oil embargo in place. This put the Imperial Navy on a timer, if it did not find a source of oil it would run out of reserves in a year. Even at this late date there were no real plans for a long war of greater than a few years, the only hope was to hit the Americans hard, then do the same to European colonies in southeast Asia, and hope to build up gains to a point where a negotiated peace was possible. This plan would not go well.