*** World War II Pacific naval campaigns -- American submarine campaign

World War II Pacific Naval Campaign: American Submarine Campaign

American World War II submarine
Figure 1.--Here we see in the smoke and carnage rising from Battleship Row at Pearl Harbor a submarine in the foreground. We are not sure what ship all the smoke is coming from at left, but that is in the general location of 'USS Oklahoma', but it may be 'USS West Virginia'. The experienced and well-trained Japanese pilots could not be bothered attacking submarines. They were after the big capital ships. As the carriers were not there, they focused on the battleships. Ironically, the battleships at Pearl by 1941 were largely obsolete. The submarines in sharp contrast proved to be one of the most potent naval ships of the Pacific War. And Pearl at the beginning of the War would be a forward base for submarine operations (COMSUBPAC). Notice the union jack flying at the bow.

"Japan's chief supply if oil came from America in the years prior to the War. Therefore since the war started our wartime requirements which amounted to about 5 million tons of oil which had to be supplied from in the Dutch East Indies. Thus the deciding factor in our defeat came from the activities of American submarines which cut off our supply entirely."

Shun Nomura, President, Mitsui Oil Company

American submariners often do not get the appreciation due. As Admiral Nimitz explained, it was the submarine force that held the line while America rebuilt its fleet. American submarines, however, were hampered by poor strategic and tactical concepts and ineffective torpedoes in 1942. The American submarines by 1943, however, began to significantly affect the delivery of raw materials to Japan. The American submarines targeted the Japanese merchant marine (maru) fleet. While the big fleet carriers got the headlines. The American submarines sunk over 50 percent of all Japanese vessels destroyed during the War. The Japanese merchant marine was almost completely destroyed, cutting the country's war industries off from supplies and bringing the country close to starvation by 1945. The American submarines did to Japan what the German u-boats tried to do to Britain. Surprisingly the 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 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 their submarines as scouts and to target warships. As the American offensive moved toward the Home Islands, the Japanese used their submarines to supply bypassed island garrisons, some of which were near starvation. They also managed to get some secret German military technology to Japan late in the war (1944).

Japanese Maru Fleet

Japan did not have a maru fleet until the early-20th century. For several centuries before Commodore Perry's Black Ships arrived in Tokyo Bay (1853), the primary Japanese interest was isolation, not marine commerce. The Shogunate was intent on maintaining a closed society and in keeping all foreign shipping away, including merchant shipping. An American naval analysts writes just before the War, "The rise in power and prestige of the Japanese merchant fleet since the advent of the iron ship is a maritime exploit of unparalleled proportions. A single generation ago Japan's merchant marine consisted of 20 sailing vessels for every steamship and the operations of the fleet were confined principally to the China service and the coastal trade. Today her shipping companies operate vessels on regular runs over the principal sea lanes of the world. Her tramps dot every ocean and compete for cargo in every port of the globe. No other merchant marine has enjoyed such a magnificent expansion in so short a period." 【McCormick, p. 1007.】 The development began only after the Meiji Restoration (1868). As a result of the Shogunate's policy of isolation, the country had no experience in international trade nor in the building and management of marine shipping industries, nor did they have the expertise needed to build a modern ocean-going merchant fleet. International shipping was dominated by American and European lines. To begin the development, Meiji authorities granted the Mitsubishi Companies monopolistic privileges and subsidies to begin the construction of a Japanese merchant marine. Mitsubishi began by purchasing used European ships with Government financing to begin operations between Shanghai and Yokohama. Small ship owners also entered the trade. The Sino-Japanese War (1894-95) stimulated the expansion of the merchant fleet with the Government buying more ships. The shagaisen owners (involved in the Shanghai trade) grew rapidly, acquiring larger ships and began operating liner service beyond Shanghai. Two important regular shipping lines (shasen) developed. The Russo-Japanese War (1905-06) had an even greater impact with the Government purchasing 177 foreign ships. And Japan with its industrial expansion began to build the shipyards capable of producing both naval vessels and merchant ships. World War I was a great boon to the Japanese merchant fleet. The War created a world-wide shortage of merchant shipping and a sharp increase in freight rates. Ideal conditions for the shipping companies to prosper. And unlike the Atlantic, there were no U-boats to contend with. The situation after the War was different. The merchant fleet had reached nearly 3,300 vessels (3.6 million tons). 【Kuroda, p. 278.】 International trade, however, never recovered from World War I. The Great Depression greatly exacerbated the situation (1930s). It was a disaster for Japanese shipping companies. The Government to save shipyard jobs introduced a 'scrap and build' system. Many older ships were scrapped and replaced with modern ships, larger (over 4,000 GRT) and faster (over 14 knots). As Japan moved toward war, the Government over saw the consolidation of the Big Five shipping shagaisen companies (Daido, Kawasaki, Kokusai, Mitsui, Yamashita) and the shasen (NYK and OSK) leading to war time control. At the time Japan launched the Pacific War, Japan had the world' third largest merchant marines after Britain and the United States. It totaled some 6.3 million GRT and was about 8 percent of the world merchant tonnage. 【Shindo】 What the Japanese did not calculate as they prepared for war was the tremendous increase in merchant tonnage that the Pacific War would require, maintenance issues, or their ability to protect merchant shipping from the U.S. Pacific Fleet.

Inter-War Developments

American admirals accepted the Royal Navy assessment that the submarine would not play a major role in future wars because of the convoy system and ASDAC. The U.S. Navy thus largely abandoned the submarine as an important vessel type. In addition American naval doctrine was for the submarine to perform a scouting role for the battleships. But the United States did not yet have the diesel engines to give fleet submarines the speed hey needed for this role. With budgets cut to the bone after World War, there was little money available for an unimportant vessel type. The experience of the S-20, that sank off Connecticut made headlines. largely because every man was saved thanks to the quick thinking of the captain. Early subs were still very dangerous, unforgiving vessels. Overlooking the smallest detail could lead to disaster. The crew had to perform with perfection. The S-20 crew neglected to close the hatch that allowed air to the diesels before submerging. As a result the S-20 sank. The S-20 was not in deep water and the captain was able to use a hand drill to make a small hole in a portion of the sub still above the surface. He was able to wave a flag signaling the need for help. Another submarine, the Squalus off Portsmouth, New Hampshire. The circumstances were similar to the S-20. The Squalus sinking, however, resulted in a major effort to develop safety technologies.This meant that submarine commanders had to be cautious with safety at the top of his priorities. This was the mindset that American submarine commanders took into he War. It was only in the mid-1930s with the rising German and Japanese challenges, that more attention was given to the submarine. American industry would finally provide the Navy with the diesel engines they needed, although not dome for the Navy. The United States had the largest rail system in the world. And it was almost all steam powered. Diesel engines began to appear (late-1920s). General Motors played a major role. We begin to see diesels in Britain Germany as well. In the United States, diesel–electric propulsion powered high-speed mainline passenger service was introduced (1934). This solved the major problem American submariners faced--under-powered boats. This was a development just in the nick of time. As a result, just months before Pearl Harbor, the United States began to launch the mew Gato-class submarine (August 1941). The Gato boats would prove to be a war-winning weapon. This provided the Pacific fleet large advanced fleet submarines which would play a key role in the Pacific War. They had long distance ranges and speed as well as offering the crews far greater creature comforts than the German U-bots or any other World War II submarines. It would take tine for the Gatos to arrive and the torpedoes problem be solved, but by late 1943, the American submarines would transform the Pacific War.

American Tactical Doctrine

The U.S. Navy's established tactical doctrine for submarines at the time of Pearl Harbor was to accompany battle squadrons, serving scout and screening functions and if possible disrupt enemy fleet formations,. possibly sinking ships. A day after Pearl Harbor, however, Washington ordered the Pacific Fleet to commit its submarines to a campaign of unrestricted submarine warfare against Japan. The German use of unrestricted submarine warfare was used by the British to paint the Germans as savage war criminals. This left the tactic of commerce raiding as a discredited measure. This despite the fact that the U.S. Navy was founded on commerce raiding. American naval doctrine was that submarines would serve as screens and scouts for the fleet. Submarine commanders were trained to be extremely cautious. The German successes in the North Atlantic during 1940 and 41 had no effect on American tactical doctrine for its submarines. No thought was given to using submarines as commerce raiders. This only came as a result of the perceived violation of international norms by the attack on Pearl Harbor and the fact that the submarines were one of the few offensive weapons left to the Pacific fleet. The problem with this, however, was that 1) American submarine crews commanders were not trained for this, 2) the commanders were not selected for their warrior spirit (like German and Japanese commanders), 3) their boats had limited range in the vast Pacific, 4) they did not have radar to help find the marus in the oceanic vastness, and to make matters even worse, 5) their torpedoes did not work. The Japanese aviators who attacked Pearl Harbor had such a low regard for submarines that the subs and their facilities were left untouched. Leaving them and the carriers which were not at Pearl the Pacific Fleets only offensive weapon. Despite all problems that had to be solved, the U.S. Navy would master all of these issues and turn the submarine force into the most effective weapon in the American naval arsenal. By the end of the War they had destroyed the Japanese maru fleet and completely cut Japan off from the resources it had conquered in Southeast Asia leaving war plants idled and its people near starvation.

Japanese Southern Resource Zone

Japan was Asia's first industrial power. Ironically it was an Asian country with very limited natural resources. From the onset of the Meiji Restoration, Japan aspired to emulate the European approach and seize a colonial empire to acquire the needed natural resources. The problem was that most of Asia except for China was already an European colonial possession. The major exception was China. So after seizing Formosa (Taiwan) and Korea, and Pacific islands, the Japanese went after China. China was militarily weak, but its immense size and stubborn resistance of its people prevented a total Japanese victory. And Japan rather than obtaining the raw materials it needed found itself in need of more raw materials to continue the war effort. After the out break of the War in Europe, the Strike North Faction gained support, but eventually collapsed and the Strike South Faction gained the ascendancy. Southeast Asia and the adjacent Dutch East Indies, offered Japan all the resources it needed, but meant war with Britain and the Dutch. This was not a major impediment. The Dutch were weak militarily and occupied by the Germans. The British were fully occupied in Europe and the North Atlantic. The United States was a very different matter. The Philippines had important resources, but could have been passed over, except for its location. The Philippines sat astride the sea lanes from the SRZ to Japan. The United States from the Philippines could have prevented the SRZ resources from reaching the Home Islands. Japan was almost totally dependent on imported oil, primarily from the United States which at the time was the leading producer. Japan imported about 90 percent of its oil. Japan had very limited oil fields and a small synthetic petroleum industry. And with an industrial economy and a large navy and merchant marine, Japan required large quantities of oil. The ongoing war in China also required oil. Japan's major source of oil was the United States. Before the invasion of China, Japan had been purchasing 80 percent of its oil in the United States (1937). The United States through its moral persuasion policy had succeeded in convincing American ship owners to reduce shipments to Japan without any formal action. Thus on the brink of war the Japanese were only obtaining 60 percent of their oil in America (1941). The Japanese were importing American oil (along with Latin American and DEI oil) in Japanese and neutral country tankers. Oil was by far the most important product needed by the Japanese, but the SRZ offered much more, including rubber, nickel, tin, rice,and much more.

Unrestricted Submarine Warfare (December 1941)

The surprise Japanese carrier attack on Pearl Harbor changed every thing -- ushering the United States into the War Americans wanted to avoid. The Japanese instantly changed a deeply divided nation desiring to stay out of the War, into a united nation resolutely determined to wage war with unprecedented force. This was important because the United States had an unparalleled capacity to wage war. It would take time to mobilize, but America had an industrial capability that no other country could come close to matching. Pearl Harbor has been discussed at length by countless authors. But one small detail rarely mentioned is that only 4 hours after the attack, Adm. Harold 'Betty' Stark, Chief of Naval Operations, sent a message to the Pacific Fleet ordering submariners to commence unrestricted submarine warfare--a fundamental departure from existing U.S. Navy policy. In fact for more than two decades since World War I, unrestricted submarine warfare had been considered a war crime. President Roosevelt referred to U-boats as 'the rattle snakes of the Atlantic', because they had adopted unrestricted submarine warfare. As far as we know, Adm. Stark acted on his own obtained no authorization for this order from President Roosevelt. Adm. Stark was the naval commander responsible for carrying out the President's directives to aid Britain in the North Atlantic and finally launch an undeclared, and totally illegal naval war in the North Atlantic (September 1941). He thus knew more than anyone in Washington how devastating submarines could be. Adm. Stark could give the order, American submariners did not, however, have the training, doctrine, or weaponry (most importantly a torpedo that worked) needed to carry out that order. It would take nearly 2 years, but American submariners would eventually put Adm. Dönitz's vaunted U-boat men to shame--with few headlines becoming the most potent weapon in the Pacific Fleet's mighty arsenal.

American Submarines

The Japanese at Pearl Harbor devastated the battleships of the Pacific Fleet. Undamaged was the submarine fleet. Thus the submarines were some of the few ships in 1942 that could take the war to the Japanese. The United States began the war with 51 submarines, 12 of which were still the old World War I era S-Class subs which proved unreliable in combat operations, even if the torpedoes functioned. Fortunately, 3 months before Pearl Harbor, the first of the new Gato-Class subs (312 feet) was launched (August 1941). The new Gato-class subs proved much more effective. They had everything the S-class subs lacked. American submarines had many advantages at the onset of the War. The first such advantage was a very effective combat command center which could very effectively plot out settings for torpedo attacks. The Torpedo Data Computer (TDC) was the early electro-mechanical analog computer used for submarine torpedo fire-control during World War II. It was the most advanced such system and constantly being upgraded during the War. The Germans had nothing to match it. The second advantage was the information available from code breaking. The third was effective radar which became available soon after the attack on Pearl Harbor and was significantly improved as the war progressed. Fourth was an extended range. The American submarines were superior to both German and Japanese subs.


Geography played a huge role in the Pacific War and the Japanese made huge mistakes based on simple geography. Imperial Japan was the first country to begin bombing cities. They began with invasion of Manchuria (1931). Not only did they bomb Chinese cities with unprotected civilian populations in Manchuria, but eventually Shanghai as well. They began doing this convinced that their own cities were invulnerable because no bombers existed that could transit the vast Pacific and reach the Home Islands. They ignored the fact that Japanese cities sere largely constructed by wood and paper. Essentially tinder for fire bombing. And the American created the B-29 Superfortress that could reach Japan. The other mistake concerned merchant shipping. They wanted the resources of the Southern Resource Zone, especially oil. Imperial planners assumed that the Americans given the vast stretches of the Pacific and their powerful navy could never cut off the flow of oil and other strategic material. Again they were badly mistaken. Just as Japan was uniquel vulnerable to strategic bombing. Resource poor Japan was also uniquely susceptible to naval blockade. Not only was the country not self-sufficient in food production, but it had few of the natural resources needed to maintain a war economy. The Americans did not have to deploy submarines throughout the vast Pacific, but only in two very small strategic choke points--the Taiwan Straits and the Luzon Straits. Actually the Imperial Navy appears to have been somewhat ware of this. Thus the Japanese did not just attack the Dutch and British to seize the SRZ, but the Americans as well because of the American presence in the Philippines. The Japanese successfully seized oil fields in Borneo and Sumatra. The oil as well as th ribber, tin, and rice from the SRZ had to pass through these two key waterways. All the Americans had to do was to deploy their submarines in these two very small waterways. As this could have been effectively done early in the War--if the Pacific Fleet subs had torpedoes that worked. Once this problem was solved in a little over a year (Late-1943-44), the Japanese Maru fleet was destroyed and Japan was cut off from the resources seized in the SRZ.

Limited Effectiveness: Tactical Doctrine / Faulty Torpedoes (1942)

The American submarine campaign was hampered by two major problems: 1) poor strategic and tactical concepts and 2) ineffective torpedoes in 1942. American naval tactical doctrine was to use submarines as scouts and screening vessels. The idea of using submarines as commerce raiders was not adopted. In fact such usage was considered a war crime. As a result, submarine captains were not trained to conduct or tactical doctrine developed. The initial American submarine campaign was also hampered by ineffective torpedoes in 1942. Many mistakes were made by the American military in the years leading up to the War. Perhaps the single most incompetent matter was the Navy's failure to develop an effective torpedo. The Navy developed a magnetically activated firing mechanism. Because of the cost, the Navy did not adequately test it torpedoes and throughout 1942, American submarines were achieving hits but the torpedoes failed to explode. The trigger mechanism had faults and the Navy had not taken into account differences in the earth's magnetic field. American submarines during 1942 averaged only about half a Japanese vessel sunk per mission during 1942. It took over a year to resolve the technical problems and effective torpedoes began to reach the American submarines. It was not until October 1943 that the American submarine campaign began to significantly affect the delivery of raw materials to Japan. The number of marus sunk began to reach sizeable numbers. American submariners sank more than 600 Japanese ships (nearly 3 million tons) in 1944, more than 1941-43 combined.

Commerce War

American naval strategists saw the American submarine fleet as serving primarily as a part of fleet operations. The Imperial Navy had the same idea. Only slowly did the idea of commerce raiding become accepted. Like Britain, heavily populated and resource poor Japan was dependent on its sea lanes. The U.S. Navy submariners succeeded in the pacific while the Germans failed in the North Atlantic. Eventually the American submarines were used to target the Japanese merchant marine (maru) fleet. Tankers in particular were singled out. While the big fleet carriers got the headlines. The American submarines sunk over 50 percent of all vessels destroyed during the War. The Japanese merchant marine was almost completely destroying, cutting the country's war industries off from supplies and bringing the country close to starvation by 1945. The American submarines did to Japan what the German u-boats tried to do to Britain. The Japanese never develop the countermeasures needed to adequately deal with the American submarines. The Japanese failed to develop a convoy system until late in the War and then it was not well implemented. One problem was that the Japanese did not have the technology to conduct successful anti-submarine warfare. The success of the American campaign was greatly aided by the fact that the American Navy by 1943 began to establish air and sea superiority in the South Pacific which it gradually extended northward toward the Japanese home islands. The destruction of the Imperial fleet in 1943 and 44 greatly reduced the Japanese ability to protect sea commerce. Eventually 8.8 million tons of Japanese shipping was sunk in World War II. Over 60 percent of that total was lost to the American submarines. 【Mawn】

Japanese Submarine Force

The Imperial Navy included a substantial submarine force. The Germans tried to convince their Asian ally to wage a commerce war as they were doing in the Atlantic with some success . The extended American Pacific supply lines would have provided countless poorly defended targets. The Japanese would, however, have none of it. Their warrior mentality meant that they wanted the glory of engage America war ships, not supply ships. The Japanese submarines targeted war ships had some success in 1942 when they destroyed or damaged American carriers. Over a ll as American ASW capabilities improved, Japanese submarine tactics proved to be an ineffective and a huge strategic error.

Allied Pacific Naval Commands

The Commander in Chief, Pacific Fleet (CINCPACFLT) was Admiral Chester Nimitz. He was the primary American naval commander during the Pacific War, appointed by President Roosevelt almost immediately after the Pearl Harbor attack. He did not, however, command all American Navy forces in the Pacific as the title rather suggests. The Commander Southwest Pacific (COMSOWESPAC) was General MacArthur. He controlled the 7th Fleet and other Naval assets, including submarines. American submarines in the Pacific were divided into two forces. Commander, Submarines, Pacific (COMSUBPAC) controlled the submarines operating from Pearl Harbor and subsequently other islands in the Central Pacific taken as the Americans rolled on toward Tokyo. The Commander, Submarines, South West Pacific (COMSUBSOWESPAC) controlled the subs operating out of Australia (Brisbane and Freemantle). This included the remnants of the Asiatic Fleet following the fall of the Philippines (April 1942). It was a multi-national force, including Dutch, Royal Navy, and Royal Australian Navy boats.


American submarine commanders, once the torpedo problem was fixed, proved to be very effective. While they get little publicity compared to the German U-boat commanders, they efficiently conducted the only major successful submarine campaign in history. Vice Admiral Charles Andrews Lockwood arrived to command the Submarine Force Pacific Fleet during World War II (January 1943). He devised tactics for the effective use of submarines. He turned a moribund force into a potent killing machine. The Pacific Fleet submarines became man for man the Fleet's most effective fighting force, largely responsible for destroying the Japanese maru fleet, crippling Japan's war making capability. Perhaps the most famed American commander was Dudley 'Mush' Morton who commanded the fabled Wahoo. He relentlessly sought out the Japanese and helped forge the way the Pacific Fleet submarine force waged the campaign. He was the first U.S. submariner to single-handily destroy an entire Japanese convoy. 【Keith】 We know very little at this time about Japanese commanders. They from the beginning of the War had an effective torpedo. They did not have the advantage of code breaking and radar that American commanders had. And the failure to wage an effective commerce war was in part due to decisions made by the Japanese High-Command as well as American ASW operations.

Waging Submarine War

Serving on an American Gato-class submarine was not easy duty. The Gato class subs marine formed the bulk of the American World War II submarine fleet. Conditions were better than aboard the German U-boats, but they were still very difficult and stressful. The Gatos had air conditioning--to prevent short circuits. But the crews benefited greatly. The food was great at first. But the fresh and frozen food was consumed in about 3 weeks after leaving Pearl and the other bases. This was the case in early in the War. As forward operational bases were won, this situation was somewhat improved. Unlike the larger ships of the U.S. Navy, there was little cold storage. The men had to rely on canned and dried foods. The crew had to stay below breathing stale air most if the time except while manning watches when the boat was running on the surface. There were long periods of no action punctuated by frightening combat. After a torpedo attack they might be subjected to a terrifying death charge attack. Medical emergencies such as appendectomies might be treated with kitchen utensils. Then there were desperate struggles to escape a sinking submarine. Some of the men were subjected to the horrors of a Japanese prison camps. 【Scott】


The Pacific fleet's submarine force operated from two different bases. Before the War, they were Pearl Harbor and Cavite in the Philippines. The Japanese carrier attack on Pearl Harbor (December 7, 1941), and subsequent Pacific offensive, left the U.S. Navy with few operational bases in the western Pacific (December 1941). The loss of Subic Bay, Cavite, and other Philippines bases was especially harmful. Operating from bases in the Philippines, The Navy could have interdicted the sea lanes between the Home Islands and the Southern Resource Zone (SRZ). This left Pearl harbor as the Navy's forward operating zone. The loss of Singapore and the Dutch East Indies (DEI) left Australian bases, especially Freemantle and Brisbane) as the other potential operating bases. Both were, however, at some distance to the Japanese sea lanes. Cavite had been an especially important sub base. A devastating Japanese air raid on the Cavite Naval Station south of Manila damaged USS Sealion (SS-195) beyond repair and destroyed the Cavite repair facility and most of the torpedoes stored there (December 10). Allied naval forces after a major defeat in the Java Sea, retreated to Australia (March 1942). American naval commanders decided to the U.S. high command decided to leave the remaining submarines of the Asiatic Fleet to operate out of Australian ports rather than joining the Pacific Fleet submarines at Pearl. They would they be in a good position there to attack Japanese sea lanes, especially oil tankers. The oil resources of the DEI and British Borneo were one of the principal reasons that the Japanese militarists launched the Pacific War. The Cavite subs were reassigned to Freemantle in Australia which was their operational base for the rest of the war. The Freemantle subs were ordered to operate in the South China Sea. MacArthur also controlled some subs operating out of Freemantle. They were at first given the added task of delivering supplies to the American and Filipino guerillas and taking off American civilian who had managed to evade the Japanese. After Midway the Japanese naval superiority was substantially reduced (June 1942). This permitted an American offensive beginning at Guadalcanal in the Solomons (August 1942). Soon offensives in South Pacific, especially New Guinea won sites for forward naval bases that could be used by both submarines and PT-boats. And offensives in the Central Pacific won additional forward operating bases. We note quite a number of forward bases for COMSUBSOWESPAC in the Solomons, the islands surrounding Rabaul, and along the New Guinea coast. These bases included support facilities for PT-boats and submarines. We are not sure yet to what extent the COMSUBSOWESPAC subs used these forward bases. The American sub base at Pearl was not damaged in the Japanese attack launching the War. The Japanese in the first two waves focused on the the air fields and capital ships, mostly battle ships as the carriers were not at Pearl when they attacked. Fortunately, Admiral Nagumo decided against a third strike which left the Pacific Fleet's subs and principal base in tact. The Pearl COMSUBPAC subs operated in the East China Sea. As the war progressed, the Pearl subs were moved forward to the Marianas which meant that their combat missions were significantly shortened. Advances in the Central Pacific meant new sub bases for COMSUBPAC at Midway, Guam, and Saipan. These were important because sub operating from bases near the Japanese sea lanes effectively increased the striking power of American submarines.

Japanese Troop Deployments

The success of the American submarines was a factor in limiting the redeployment of the very substantial Japanese Army in China to man the Japanese Pacific bastions and the Philippines. 【Parish】 Put men and supplies on a Maru exposed them to American submarine attack. This was not a serious problem in 1942, but the American submarines began to bight in 1943 which was when the Japanese needed to strengthen their bases in the southwest Pacific which were under increased Allied (American and Australian) attack. The American subs also made it difficult to supply the troops that were deployed to the Pacific. This was something that Imperial Headquarters needed to consider as the power of the Imperial Fleet declined. Getting men on a Pacific island, was just part of the problem for the Japanese. They then had to be supplied. And on New Guinea and most small islands, local food was scarce or unavailable. Orders from Tokyo were 'self sufficiency'. This essentially ordered many garrisons to starve.

Anti-submarine Warfare

As a result of the Battle of the Atlantic struggle against the German U-boats, America and Britain launched a major scientific and technical effort to develop ASW technology even before Japan launched the Pacific War with the strike on Pearl Harbor. Major advances were achieved and by late-1942 had begun to reach the fleet. Here the greater scientific and industrial capacity of America and Britain were major factors. In contrast, the Japanese made little progress in developing effective ASW technologies despite the critical importance of protecting the Maru fleet. Japan was even more dependent on food and raw material imports than Britain. Not only did the Japanese not develop effective ASW technologies, but the sizeable naval and air losses as the war progressed, significantly attrited the ASW capabilities that Japan had at the beginning of the War. This was primarily escort craft.

Covert Operations

The primary task assigned to American submariners was severing the Japanese sea lanes so that raw materials from the SRZ could not reach the armament factories on the Home Islands. This was, however, not the only roles assigned to the submariners. In addition to rescuing downed airmen, submarines were used for range of covert operations. They included supporting resistance groups, rescuing American and European civilians, and attacks on isolated Japanese outposts. The idea was to avoid fire fights, but this was not always possible. One raider reports, "Immediately upon landing, a searchlight was turned on and something like a challenge shouted by someone on the beach with barking dogs. I had eased off the stern of the runner boat and was in water just above my knees. I assumed this was not a friendly spotlight. Fortunately, I had not been spotted and shot the searchlight out with a short burst of my BAR. A uniformed Jap, judging from his seemingly wrapped leggings and cap, came charging at Gunner Carrinder. He came at full speed with rifle and fixed bayonet. Kahler was directly in front of me, about ten yards ahead, and Ed Heinz was about the same distance on my right flank. With the searchlight out of commission, I shifted my position and directed my fire to take care of the Jap charging Carrinder, who seemed to be close enough for hand-to-hand combat. As I commenced firing I breathed a silent prayer that I wouldn't hit Gunner. I would be close and Carrinder was never the forgoing type. When I saw tracers from my fore tear in to enemy I felt relieved." 【Monroe-Jones and Green】

Spyron: Philippines Spy Operations

With the exception of China, most of the areas occupied by the Japanese were European colonies. The Philippines was an American commonwealth, but about to be granted independence. Thus unlike the situation in Europe, these were not fertile grounds for building a resistance movement. One exception was French Indochina. Here there was not so much support for the French as opposition to the Japanese. Another exception was the Philippines. There was considerable support for the Americans in the Philippines, both because of the progressive American colonial administration and the upcoming granting of independence. As a result, a substantial resistance movement developed in the Philippines. MacArthur used some of the submarines based in Brisbane for supply and intelligence operations, but not to the exclusion of offensive submarine operations. Lt.Cmdr. Charles 'Chick' Parsons, a naval Reserve officer, was put in charge of the spy squadron (SpyRon). Parsons had managed a stevedore company in the Philippines until the War. The Japanese captued him when Manila fell, but he was repatriated because he was serving as Panamanian consul. The repatriation ship Gripsholm brought him to safety. He then joined the War and was inserted in the Philippines to organize, control, and supply resistance operations. SpyRon inserted 330 agents and landed 1,325 tons of supplies. The submarines in addition to landing supplies brought 470 people to safety in Australia. There were 19 submarines participating in the Spyron missions, but most of the work was done by USS Narwhal, USS Nautilus, and USS Stingray. 【Jones and Nunan, p. 218.】 By the time the Americans landed on Leyte, a force of 180,000 guerillas were active in the Philippines.

Small Craft Attacks

Submarines could strike without surfacing with torpedoes. Once the initial problems with American torpedoes were corrected, the submarines rapidly destroyed the Maru fleet. Torpedo attacks were the safest way of sinking an enemy ship because it could be done without surfacing and exposing the submarine. This of course is why the Germans insisted in pursuing unrestricted submarine warfare in World War I. The American submariners by 1944, significantly reduced the number of large targets justifying a torpedo. And as operations shifted closer to the Home Islands, the targets increasingly became small ships. This required the submariners to surface and use the deck guns or even explosive charges. These targets were sampans, fishing boats, and other small craft. One author describes the attacks, ":For a submarine crew there was no maneuver more exhilarating, or more fear-inducing, than a surface gun action. Relying on surprise and speed, the submarine could suddenly punch through to the surface, while half-drenched sailors scrambled through the hatches to reach their guns and ammunition lockers. A crack team aimed to get off the first shots within 20 seconds of surfacing. Men who were usually kept cramped beneath the sea were at last unleashed to encounter the enemy face to face." 【Sturma】

American Losses

The success of the American Pacific submarine campaign did not come without substantial losses. The Navy lost 22 percent of its submarines deployed in the Pacific. This was the highest loss ratio experienced by any American combat operation during the War, although only a fraction of the losses experienced by the German U-boat and Japanese submarine fleets.

Table 1.--Japanese merchant marine shipping
sunk (1941-45).

Combat Groups Tons* Percentage
Submarines 4.9 million 54.6
Navy Carrier Air 1.5 million 16.3
Army Air 0.9 million 10.2
Navy Land Based Air 0.4 million 4.3
All Other Causes 1.3 million 14.5
Total 8.9 million 100 percent
*Tons sunk include only ocean going Marus (ships over
500 gross tons) sunk or disabled for the duration of the
war. Included are ships sunk by Allied submarines (2%),
by Allied aircraft (12%). 23% of those sunk during the
month of July 1945 were sunk by Allied carrier based
Source: William P. Gruner. "U.S. Pacific Submarines in World
War II". (Historic Naval Ships Association: 2010).

Japanese Losses

The cost to American submariners was high. The Japanese paid, however, a much higher price than the American submariners. And the ships lost were never made up by increased production. The Japanese had a limited ship building capacity. And most of their shipyards received orders to build needed combat ships. American submarines in addition to hits on the combat vessels of the Imperial Fleet, essentially destroyed the Japanese Maru fleet. American submarines were the only effective weapon against the Japanese Marus feeding the country's war economy during the first 2 years of the war. 【Gruner】 After 1943 with growing American air and naval power, other elements of U.S. forces began to contribute to the effort. All in all, American submariners were responsible for sinking over half of the Maru fleet (table 1). The Japanese were left without any way of transporting the critical resources of the SRZ back to the factories on the Home Islands. Surviving Japanese war ships were in port without fuel and civilians were reduced to virtually starvation rations. The submarines also sank over a third of the Imperial Navy's major ships (ships larger than destroyers). An Imperial Fleet commander reports that "Our records show that about 36 percent of the major vessels, that is vessels larger than destroyers, were destined by Unites Stares submarines." 【Nagano】 Here the surface fleet including naval aviation did more, but the submarines achieved their tally at a tiny fraction of the cost of the surface fleet.

Japan and Oil

Modern war requires oil. All three Axis countries had a significant problem. They were not self-sufficient in petroleum. Each of the Axis countries attempted to resolve this limitation to varying degrees of success. Japan would require huge quantities of oil of it planned to wage a naval war in the vast stretches of the Pacific. Japan had to import almost all of its oil in peacetime and war would significantly increase the quantities required. Japan was a densely populated, resource poor country. Expansion into Korea and Manchuria (Manchuko) managed to acquire many needed resources. The most critical resource that Japan lacked was oil. And to make matters worse, the United States was the major world producer of oil. America was also Japan's principal supplier--the same country the United States would have to fight if it was to seize an empire in the resource-rich South Pacific--especially the DEI which had developed important oil fields. The United States attempted to dissuade Japan from waging aggressive war in China. The United States began a series of trade restrictions until it became clear with Japan's move into southern Indochina that Japan was preparing to launch a major aggressive war in the Pacific. America responded with an oil embargo. This action made war inevitable. It only became a question of when and where Japan would strike. Japan had oil stockpiles that could supply its normal needs for 2 years, but only about 1 year if Japan went to war because of the huge increased requirements to fight a naval war. This set in motion a time table. Japan had either to decide to cease aggression in China or go to war before it ran out of oil.

American Submarines and Japanese Oil

Japan went to war with the United States to obtain the oil needed to complete the conquest of China. Ironically while conquering the Southern Resource Zone SRZ with important oil resources, Japan never approached its pre-War supply of oil (1940). The United States had been Japan's major supplier. And because of Japan's continued aggression in China as well as southward movement, the United States embargoed oil exports to Japan (July 1943). Needed imports as a result plummeted (1941). While the British and Dutch attempted to destroy the oil fields and refineries, the Japanese had them functioning again relative quickly. There were modest increases in oil deliveries (1942 and 43), but still only a fraction of pre-War deliveries. The first quarter of 1943 was the peak War-time period for Japanese oil imports. The Japanese Imperial Navy required at least 18 million barrels for war time operations. The Imperial Army needed another 6 million barrels. 【Mawn】 For comparison, the United States used some 45 million barrels (1942) and that was before the major build up the Big Blue Fleet and Army and Air Force operations began. The American improvements in tactics and a working torpedo began to affect results (late 1943). American forces succeeded in cutting Japan's oil lifeline, already inadequate, by half (1944). This was largely because of American submarine attacks on the marus, including tankers. Then Japan was virtually cut off from the oil fields in the SRZ. American submarines, a very small part of the naval force, were responsible for over 50 percent of the Japanese vessels sunk. The Japanese controlled fields in the SRZ were producing important quantities of oil. Getting to the Home Islands was another matter. The oil field were producing some 130 million barrels, but only about 45 million barrels (35 percent). Japanese refineries on the Home Islands were not receiving the crude oil so they need to produce refined product. Then the U.S. bombing began in 1945. More than 65 percent of the Japanese total refinery capacity was destroyed. Not only was the Imperial Navy affected, but also Japanese air forces. The resulting shortage of aviation fuel forced a substantial reduction in air operations and pilot training. Navigation courses were neglected. Japan turned to the development of Kamikazes which only need the fuel for short one-way flights. Unlike the Americans, the Japanese did not return skilled pilots for training roles at the flight schools. They were kept in combat roles at the front.


Gruner, William P. "U.S. Pacific submarines in World War II". (Historic Naval Ships Association: 2010).

Jones David and Peter Nunan. U.S. Subs Down Under: Brisbane, 1942-45 (Annapolis: Naval Institute Press, 2005).

Keith, Don. Undersea Warrior: The World War II Story of "Mush" Morton and the "USS Wahoo" (2011).

Kuroda, H. Sehai Kaiun Shi (Tokyo: Seizando, 1972).

McCormick, Harold A. "Japanese merchant marine," Proceedings Magazine Vol. 62 No.7/401 (July 1936).

Mawn, Paul E. "Oil & War."

Monroe-Jones, Edward and Michael Green. The Silent Service in World War II: The Story of the U.S. Navy Submarine Force in the Words of the Men Who Lived it (2012), 352p.

Nagano, O. Chuief of IJN General Staff. Interview in the U.S. "The Big Picture" TV series.

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

Scott, James. The War Below: The Story of Three Submarines that Battled Japan (2013), 448p.

Shindo, Tadaaki. "A brief history of the Japanese merchant marine fleet," Keio Journal of Economics Vol. 75, No.? (February 1983), pp. 1034-55.

Sturma, Michael. Surface and Destroy: The Submarine Gun War in the Pacific, 280p.


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