US submarine war Pacific 1941 - 1945


  in the PACIFIC  1941 - 1945


Silent Victory:
The U.S. Submarine War Against Japan

By Clay Blair Jr.

The definitive history of unrestricted submarine warfare in the Pacific




WWII U.S. Submarines at War in the Pacific
 A history of the U.S. Silent Service in World War II and
unrestricted submarine warfare against Japan 1941 - 1945


The island hopping war waged against Japan posed terrific challenges for the United States armed services during World War II. Committed to a war in two theaters of operations, the logistics of moving man and machinery over vast expanses of the Pacific Ocean against a seasoned and tenacious enemy was an obstacle that certainly had to be overcome if the war against Japan was to prove to be victorious. Many of these  same issues held true for the Japanese, only to a much greater degree. Highly dependent on imports, this island nation's lifeline was the sea. 

During the 1930's many believed that a war in the Pacific was inevitable. Serious concerns over aggressive Japanese imperialism led to the imposition by the United States of potentially debilitating sanctions of raw materials. With the armed conflict raging in Europe, the isolationist American leadership sought to avert committing itself to open hostilities, although clandestine material support of America's European allies was actively in progress. Negotiations between the United States and Japan had been ongoing for months. Japan obviously wanted an end to U.S. economic sanctions. The Americans demanded that Japan pull out of China and Southeast Asia and for her to repudiate the Tripartite "Axis" Pact with Germany and Italy before those sanctions could be lifted. Neither side was willing to budge. President Roosevelt and Secretary of State Cordell Hull were anticipating a Japanese military strike as retaliation - they just didn't know where. The Philippines, Wake Island, and Midway Island were all very strong possibilities. American intelligence reports had sighted the Japanese fleet movement out from Formosa (now Taiwan), apparently headed for Indochina. The U.S. State Department demanded from Japanese envoys explanations for the fleet movement across the South China Sea but they claimed ignorance. U.S. military intelligence reassured the president that, despite understandable fears, Japan was most likely headed for Thailand and not the United States.

Unfortunately, the predictions of an armed conflict were about to become a reality on 7 December, 1941 when the surprise attack by Japanese forces against the United States Naval base at Pearl Harbor, Hawaii proved to be a decisively overwhelming success for the enemy. The bottom line was that the nation of Japan ultimately went to war when the imports of her vital resources were threatened. Severely overpopulated, their goal was to assure that this supply of goods and raw materials would continue undisturbed.

The Japanese attack on Pearl Harbor was a bold, calculated attempt to gain the  military advantage against the nation that was at the root of her economic and industrial concerns. Knowing that the United States was rich in resources and capable of a considerable military might, Japan's initial effort to secure the dominating control over the Pacific was unleashed on that "day that will live in infamy". Their plan being that a decisive, crippling blow to the Pacific fleet would destroy the United States' morale and her willingness to fight. Believing that the American masses were committed to a political philosophy of isolationism, Japan would soon discover that this was an extremely serious miscalculation of the American fighting spirit.

In a matter of a little more then two hours, the Imperial Japanese Navy inflicted a potent, punishing blow to the U.S. Pacific fleet anchored at Pearl Harbor, with more than 2400 naval personnel killed and over 700 wounded. All but the battleship Pennsylvania either lost or out of commission for more then a year. Two thirds of the US Army Air Force aircraft were destroyed along with 196 navy/marine corps fighter planes. In short, the Pacific U.S. surface fleet was decimated. Ironically, the Japanese planes barely even buzzed the American submarine base. The adjacent fuel depot and ammunition dumps emerged unscathed from the attack; possibly nothing more than an oversight at the time but an error which would eventually be proven to have been a grievous military blunder. 

The escalation of tensions during the latter part of the 1930's indicating the possibility of a war in the Pacific led the US Navy to actively develop a submarine capable of supporting surface fleet operations. The desired "fleet boat" would be required to possess the speed, the range and the ability to maintain extended deployments which would be necessary for a war in the world's largest ocean. Various classes of submarines were designed and commissioned but regardless of the many technological improvements made to the American submarines, the U.S. Navy's submarine force was caught woefully unprepared for the type of warfare which they were about to face. All of the pre-war, peacetime training for the U.S. submarine commanders which was previously geared in support of the surface fleet, was now obsolete and impractical. Submarines were originally looked upon to serve as scouts and screens for the navy's capital warships. Unfortunately, following the devastating attack on Pearl Harbor virtually no surface fleet of any consequence remained in the Pacific waters for which to scout or screen. The United States Navy developers of tactical planning for submarine warfare never anticipated the situation that they found themselves in during those early days of the war. With the American Navy in the Pacific all but destroyed, the rules of submarine warfare had to be drastically changed.


On December 7th, 1941 there were twenty one submarines attached to the U.S. Pacific Fleet based in Pearl Harbor: six V class, three of the P class and twelve T class subs although only eleven boats could actually be considered available for combat operations. Four were in Pearl Harbor at 7:55 am when the Japanese began the attack. The USS Narwhal, Dolphin, and Tautog were tied up at the sub base finger piers while the USS Cachalot was in the navy yard for repairs.  As the first bombs began to fall on Ford Island Naval Air Station, the crews of the moored subs sprang to action and began firing on the Japanese torpedo bombers tracing their way to Battleship row (The USS Tautog is credited with downing a Japanese Kate bomber). By 10 o'clock, the attack was over. The submarine base survived undamaged, although a crewman was wounded during a strafing run. Following the attack, the American submarine fleet received at 4:00pm on the afternoon of 7 December 1941 orders issued by Admiral Harold Stark, the Chief of Naval Operations, for all available boats to immediately put to sea and for those already underway to conduct "unrestricted submarine warfare" against anything Japanese. The primary task of  of the United States fleet was to attack heavy ships (defined as a battleship, aircraft carrier, cruiser etc). It is important to note the gravity of this very powerful decree. The United States, by calling for unrestricted submarine warfare, officially renounced article 22 of the London Naval Treaty of 1930 which formally spelled out the guidelines and procedures that a submarine was required to follow when attacking an enemy non combatant vessel. The London agreement of course permitted aggressive operations against an enemy warship, however it demanded that the attacking submarine inform a merchant vessel of the its' intention to sink it; allowing passengers and crew the opportunity to abandon ship prior to any hostile action. While this was certainly a gentlemanly way to wage war, militarily it was largely unfeasible and extremely dangerous for the submarine. To be in compliance with the agreement, the submarine would have to leave the relative safety of the ocean's depths by surfacing, rendering her highly vulnerable to an air attack or a counterattack by the an enemy warship. The U.S. rationalization for dismissing the London Treaty was that Japan's attack on Pearl Harbor constituted a serious breach of international law. Further the U.S. anticipated that Japan would arm and escort her merchant fleet. Finally, owing to the fact that all Japanese marus (merchant ships) would fall under the direct control of Japan's military, the United States would be absolved from observing treaty restrictions and any offensive operation against a merchant vessel was justified as enemy merchant ships were no longer  "non combatants". With the attack on Pearl Harbor and the CNO's call for unrestricted warfare, U.S. submarine commanders now had free reign and the blessing of the Naval High Command to seek out and attack any ship flying the flag of the Rising Sun.

Previously during peacetime, strict adherence to the London Treaty of 1930 was understood and absolute. As a result combat training concentrated solely on offensive operations against the swifter warships and not against the slower, lumbering merchant vessels which they were now permitted to target and engage. Untrained for waging this type of search and destroy mission, it is small wonder that the submarine commanders recorded poor initial tallies. Much can be attributed to the fact that caution seemed to be the watchword for the submarine fleet. Tactical peacetime doctrine demanded that attacks against enemy vessels were to be made from deep submergence and well below periscope depth using only sonar bearings in which to develop an acceptable firing solution. Surface attacks, which proved to be such an important tactic of the German U-Boats in the Battle of the Atlantic,  were out of the question for U.S. submarines. In addition, it was discovered that from the air a submarine could be detected to depths of over one hundred feet during conditions of optimal visibility so all submarines were required by orders to remain submerged within 500 miles of an enemy airfield. This only tended to reinforce the belief that operational caution was critical, thus compounding the poor performance of American subs early in the war. Few skippers were willing to buck the pre-war rule book by coming to surface or periscope depth for an attack. All were career officers, generally older and thus much more conservative and cautious in combat. Consequently, most of the early offensive maneuvers were made from the safety of deep water by sonar, with predictably dismal results. The lack of offensive initiative and flawed doctrine however were just a part of the problem. Defective torpedoes was an issue that would severely reduce the submarine fleet's effectiveness during the first few years of the war. Additionally, the lack of a unified submarine command compounded the challenges. Infighting between the Pacific Fleet based in Pearl and the Asiatic Fleet in Manila for manpower and materials accounted for a schism in command that lasted throughout virtually the entire war.

Fortunately, major intelligence advances were being made at this time by the United States in intercepting and deciphering Japanese communications. The three cryptanalysis units, Cast (Cavite, Manila Bay), Hypo (Hawaii) and Negat (Navy H.Q., Washington) were highly successful in breaking the latest Japanese code. Luckily, the Japanese were a talkative bunch, and messages concerning their movements, strategies and plans were frequently broadcast over their military airwaves. Possessing the ability to decipher the communications, the US codebreakers would forward this  critical information to submarine captains in the form of the famous "Ultra". This top secret skill was so closely guarded that one submarine division commander chose to stay with his sinking boat when his sub broached after getting depth charged and being hammered on the surface by gunfire from an IJN destroyer. Choosing to remain on board the sinking USS Sculpin, Captain John P. Cromwell was posthumously awarded the Medal of Honor for his actions in avoiding capture with the possibility of being subjected to torture and giving up the secrets about Ultra and naval operations in the Pacific. But even with the "heads up" intelligence information being provided, tactical positioning errors by top leadership continued to haunt the submarine fleet. Boats were continually given orders of deployment to stalk the entrances of harbors and ports, ignoring the fact that the bulk of the Japanese shipping was concentrated along established, high seas trade routes. The decision to retire the S-Class boats from active combat duty resulted in the reassignment of seven fleet boats from the Asiatic Fleet to the Solomons for picket duty. With fifteen boats based in western Australia, this move had essentially cut the Asiatic Fleet's complement in half, leaving fewer submarines available to actively hunt for Japanese merchant and military shipping. 

When the war began, U.S. submarines had no RADAR (Radio and Detection Ranging) but by August of 1942 an air search system (the SD) and the first surface search RADAR system (the SJ) was installed aboard a US submarine. The SJ RADAR although it still was unfortunately full of kinks, was a tremendous boost to navigation and surface vessel detection and location. In addition, the new Gato class boats were arriving on a regular basis to replace and reinforce those battle weary subs which had been bearing the brunt of the war so far. While armed with an established set of patrol and attack guidelines at the war's outset, boat commanders were finding that they were actually in a "learn as you go" situation. As a result new tactical procedures were being developed, often times much to the displeasure of their superiors. For once however, things began to look favorably for the US sub fleet. At least for a brief period. Torpedo failures were numerous and succeeded in handcuffing many skippers. BuOrd (Bureau of Ordnance) held steadfast to the opinion that human error was the the cause of the torpedo troubles, and not a design flaw. Compounding the sub fleet's problems, poor tactical positioning on the part of the top Navy brass continued with a seeming vengeance. The Pacific submarine forces were often split up, and the deployment of boats out of high contact areas to patrol zones that were considerably poorer in productivity occurred frequently. 

By early 1943, the US had begun limited use of a proven cooperative attack tactic known as "wolf-packing". An important part of Germany's U-boat success in the Atlantic, the US wolfpacks returned mixed results. Confidence in the ability of two or three fleet boats to execute a cooperative attack against any enemy vessel ran high, but the dedication of these subs to a single attack was considered by some to be a poor use of military assets. Japanese convoys operated with a far fewer number of ships then did those merchants transiting the Atlantic and getting thinned out by the extremely efficient U-Boat wolfpacks. there were considerable difference in the High Command of U.S. and German submarines. Admiral Karl Dφenitz, the commander of the U-Boat arm of the German Kreigsmarine, virtually micro-managed his boats movements and maintained almost continual radio contact with his boats, directing many of the operations.


Torpedo problems plagued the fleet submarine throughout much of the war, but the early years proved to be the most trying time for sub skippers regarding the ordnance they carried. Malfunctioning torpedoes were reported by boat captains from the onset of hostilities and the response from BuOrd was always the same: The weapons were fine, it was the crew's inabilities that were to blame. History has proven otherwise. 

US fleet submarines went into battle armed with the MK XIV steam torpedoes which were equipped with the MK VI influence exploder. The design behind the exploder was to allow the torpedo to detonate within the magnetic field under the keel of the target boat, effectively breaking the ship's back. This "top secret" device was highly regarded by the Navy which believed they possessed a device that would revolutionize submarine warfare. In fact, they so tightly guarded the information about the MK VI that they conducted few actual tests. In addition, training in its' use was restricted for fear that the secret about this lethal miracle might leak out. During the same time the US was tenaciously safeguarding the MK VI, both Britain and Germany abandoned their use of a similar devices they had developed due to the equipment's unreliability. Skippers complained that, after developing an ideal attack setup, their torpedoes would detonate prematurely, miss completely or not explode at all. In December of 1941, after having fired in excess of 70 torpedoes at 28 targets only one hit was recorded. Theories as to the cause were widespread. The most popular being that the weapons were running deeper then they were set. Report after report of potentially faulty torpedoes came down the pike, only to be officially attributed as "crew error". Resolution to the problem took its first step forward when in June of 1942 RADM Charles Lockwood, a submarine veteran, was assigned the command of the Asiatic Fleet. His first order of business was to test the MK XIV for running depth. His findings were consistent with the reports from the submarine commanders: the MK XIV ran deeper then their settings. The skippers were advised to adjust the running depth accordingly in the hopes of correcting the defect. Unfortunately, the number of sinkings and total tonnage scores remained disturbingly lower then expected. Continuing on the belief that the poor showing was due to ineffective skippers, many were relieved of their commands, replaced by younger, more aggressive officers.

If the possibility of conducting a war patrol armed with faulty torpedoes was not a huge enough problem, the shortage of their supply, defective or otherwise, was. Political arms limitation agreements prior to the war restricted the ability of countries to produce certain weapons. Even with the advent of antisubmarine technology, submarines themselves were considered to be an extremely deadly weapon of war, and there was a worldwide effort to restrict their production. Rules of engagement even set boundaries as to how a submarine could be employed. The United States entered WW II with an inadequate supply of torpedoes and too few facilities to produce the numbers required. The resulting shortage severely handcuffed skippers during a patrol. By November of 1942, Pearl Harbor's supply had dwindled down to zero. The Navy issued guidelines detailing the number or torpedoes that could be expended on any one target.  As a result, many potential targets escaped. 

By 1943, with the submarine fleet still unable to prove their overall effectiveness, boat captains were once again casting the blame for their troubles on faulty ordnance. Patrols returned to base with tales of torpedoes which would explode about half of the time. Finally convinced that the MK VI influence exploder was the culprit, Lockwood ordered them to be disconnected. But the saga of defective weapons continued. As numerous patrol reports continued to describe perfect set ups followed by torpedoes striking the targets but failing to explode, (one account detailed an attack where 13 out of 15 hits did not detonate) Lockwood ordered new tests to be conducted. Firing torpedoes at a vertical cliff face, the duds were closely examined. It was determined the when a torpedo struck at a 90Ί degree angle (which was considered ideal) the firing pin would often become distorted before it could contact the explosive cap. The results confirmed what many had feared, that submarines went into battle armed with defective weapons. Installing a stronger firing pin resolved the issue of malfunctioning torpedoes virtually overnight. The resulting dramatic increase in tonnage scores removed any doubt as to the cause of the problem that bedeviled the submarine fleet during the first few years of WW II.  


Towards the end of '43 the situation for the US submarine fleet had begun to improve considerably. The arrival of newly commissioned boats was exceeding the total number of losses and the difficulties regarding malfunctioning torpedoes was in the process of being resolved. As a result, the submarine  fleet was steadily inflicting severe damage on enemy shipping (by the close of that year, US submarines had sunk over 1, 500,000 GRT of Japanese merchants). Moreover, the re-evaluation of patrol zones by RADM Charles Lockwood resulted in boats being  deployed to areas that would allow for an increased number of contacts. The allied victory during the Battle of the Philippine Sea dealt a devastating blow the to the Japanese military machine. Three of five IJN aircraft carriers were sunk (two by submarines) and the substantial loss of aircraft basically all but terminated the Japanese Naval air force. A new directive was issued to the US submarine fleet ordering the targeting of Japanese oil tankers in an  effort to cut of their fuel supplies throughout the Pacific. With US submarines sinking enemy vessels at a rate of 50 per month in 1944, the picture looked bleak for Japan. Serious supply shortages were effecting their ability to continue the war effort . The conflict they initiated several years prior was looking more and more apparent to end in certain defeat. However, their determination and resolve never wavered.  Still to come were the battles for Okinawa, Luzon, Formosa and Iwo Jima. As the Japanese fleet retreated to areas where crude oil was available, allied forces were able to establish advanced naval bases which reduced the tremendous transit time from the main sub bases to the patrol zones.

US codebreakers were picking up messages which proved highly productive on a regular basis and by the early months of 1945 the hunting grounds of the US submarine fleet were getting thin. The number of prize targets had dwindled down to a precious few owing to the devastating impact the silent service had on merchant and military shipping. The decreasing number of available targets thus prompted a shift in how American subs were utilized.

With the knowledge that Japan's merchant fleet had been seriously and substantially degraded, the civilian sampans became the ever increasing target of American submarine searches and attacks. It was reasoned that these small, flat bottomed fishing vessels could be the  alternate, desperate means of shipping that the Japanese were employing to run supplies. US submarines would typically surface and board these boats in search of military contraband; sinking those that were found to  be holding ammunition and other obvious materials of war. Anticipating the invasion of the Japanese homeland along with the opportunity to break into the Sea of Japan (which still sheltered enemy shipping) saw submarines employed in both mine detection and photo recon missions. Not since Mush Morton and the Wahoo had U.S. submarines attempted to reap the bountiful rewards of conducting a war patrol in the Sea of Japan. Generally shallow in depth and safeguarded by heavily mined approaches, this target rich area was considered too dangerous a place to hunt. The introduction of the FM sonar, originally developed for mine sweepers, provided the needed technology to accurately locate and chart the previously impenetrable mine fields. The end of the war was at hand. Hiroshima and Nagasaki guaranteed it.


The overall impact that the United States Navy's submarine forces had on the outcome of the war in the Pacific is often understated. The modernization of the world's navies during the WW II era saw an incredible shift from the dependence upon the battleship towards the aircraft carrier and its' support groups. The recognition and glory which has been showered upon this formidable arm of the US Navy is, without question, certainly warranted and deserved. But to study the Pacific theater without looking closely at the battle figures compiled by the Silent Service would be a grave injustice to any student of the war and to the valiant men who unselfishly gave of themselves. Comprising less then 1.6% of all US Naval personnel in the Pacific, yet accounting for more then half of all enemy shipping sunk, the US submarine fleets were well represented in the Allied effort for achieving victory. Historians have stated that a major factor contributing to Japan's surrender was this island nation's recognition of the fact that she was unable to sustain the war effort due to the severe shortages of raw materials and basic essentials. By eliminating their ability to import vital goods and supplies, American submarines were able to do to Japan what Hitler's U-Boat force came close to doing to England.
The officers and men of the US Silent Service, having had to re-write wartime tactical doctrine on the fly, were undoubtedly modern military pioneers. History has provided a place for these valiant sailors and the incredible deeds they performed by securing a prominent position in the expansion of any nation's naval fleet for a powerful submarine force. The final tallies show that of the 10 million tons of military and merchant shipping lost by the Japanese during WW II, US submarines accounted for a total of 54%. The interesting question remains as to how much earlier could the war have been brought to a close had the US submarine fleet been initially equipped with reliable torpedoes. The overall effectiveness of the submarine war and the tremendous contribution that the men of the silent service made towards its' final outcome is truly historic. 






Resources Notes:

Product photo

United States Submarine Operations
in World War II

Theodore Roscoe
US Naval Institute
Copyright 1949

Product photo

War Beneath the Sea: Submarine Conflict During World War II
Peter Padfield
Wiley & Sons Inc,
Copyright 1995

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