During World War II, all major belligerents fielded submarines of one kind or another, and each met with different levels of challenges and successes. The German Kriegsmarine and the American Submarine Service in the Pacific received a lot of press for the numbers of tons of shipping sunk at their hands, but also the number of boats and sailors they each lost beneath the waves. When World War II began, the Japanese Navy had 63 ocean-going submarines with an additional 111 new ocean-going submarines constructed by the war’s end. The last prisoners of the war were the crews of the Japanese I-14, I-400, and I-401, captured at sea in the weeks following the end of hostilities on August 15, 1945. Of the 174 Japanese submarines, 128 of them were sunk by various means. The loss of 74% of the Japanese submarine fleet was not dissimilar to the Kriegsmarine losses during the war.
The Japanese submarine force was initiated in the early days of submarine warfare. The Japanese maintained submarines as early as 1904 when Japan purchased five Holland-type submarines from the Electric Boat Company in Groton, CT. The submarines were originally built in the U.S. and then shipped to Japan, where they were reassembled. The first Japanese constructed submarine was completed in September 1905 at the Kawasaki Dockyard Company in Kobe, Japan. It was based on plans of a modified Holland-submarine purchased from the United States. These American variations and the several British C-class submarines purchased from Great Britain became the basis of the Japanese First Submarine Squadron. established at Kure Naval Arsenal around 1905. In 1909, the Japanese first submarine tender, the Karasaki, was placed into commission. A submarine tender is a surface vessel that has machine shops for repairs, storage for spare torpedoes and other ammunition, and additional spaces for medical attention and general rest for submarine crews. Submarine Tenders, in both the US and Japanese navies, act as the submarine command headquarters or flag ship.
Like the rest of the Allies during World War I, the Japanese benefited from the captured technology of the defeated Imperial German Navy and the advances they made in submarines. But like other world powers, the Japanese confronted the diplomatic and moral issues of Guerre de Course (commerce raiding), taking a philosophical stance that submarines would only be involved in fleet actions with naval vessels and not be used against merchant shipping. In part, this strategic plan was based on Japan’s love of Alfred Mahan’s naval theory of the “Decisive Action,” as explained in his popular book, The Influence of Sea Power Upon History. In short, the “Decisive Action” occurs in an all-in battle between two great naval fleets, when whoever is left standing commands the lines of communications (sea lanes). This is an advantageous position to be in because the winning navy can then move without challenge to support their amphibious and ground forces. An example of this can be seen during the Battle of Tsushima in May 1905, when the Japanese Navy defeated the last of the Russian fleets (the Baltic Fleet) and the Russians could not prevent Japan from supporting their troops from the sea.
In future wars, the submarine became a weapons platform that was considered revolutionary in fleet operations. This led Japan to develop different types of submarines, including the small two-man Type A (Kō-hyōteki-class) like the ones used during the attack on Pearl Harbor, also known as the “midget submarine”; RO-class, medium range ocean-going submarines; and the I-class long-range “fleet” submarine. Within the I-class, there were unique developments like mission purpose construction, an advanced-attack submarine with additional torpedo tubes, and a command-and-control submarine that had a small watertight hanger built into the conning tower for a small float plane. The plane was useful for reconnaissance in the age prior to RADAR. Later during the war, this concept was modified for the giant Sen Toku submarines (I-400’s) by adding a hanger and storage space for three attack float planes and ordnance of torpedoes and bombs.
The Japanese Submarine Force was organized under the 6th Fleet of the Imperial Japanese Navy (IJN), which was established in 1940 prior to the escalation of the Pacific War. The 6th Fleet was originally in command of three submarine squadrons (SUBRON 1 to 3). After the United States and Great Britain entered the war in 1941, the primary mission of the Sixth Fleet was performing reconnaissance along the West Coast of the United States and patrolling the sea lanes (lines of communication) between the U.S. and Australia, and in the Indian Ocean along India, East Africa, and approaches from the Suez Canal via the Red Sea. In addition to providing reconnaissance, Japanese submarines were used early in the war during several battles, including the Naval Battles of Guadalcanal where the USS Juneau (CL 52) and the USS Wasp (CV 7) were sunk, and to mop-up operations following a naval action such as in the Battle of Midway, when Japanese subs attacked damaged American ships, resulting in the loss of the USS Yorktown (CV 5) and the USS Hammann (DD 412).
Despite their successes against warships and their original philosophy of a decisive action and confronting combatant ships, the Imperial Naval Headquarters decided that submarines should start commerce raiding and attacking merchant shipping. But the fates were not in their favor. By the time this shift was implemented, the U.S. Navy had adapted due to hard-earned lessons from the Battle of the Atlantic and fighting the German U-Boats. Convoys and escorts were no longer easy prey and fought back with deadly responses. The American submarine campaign in the Pacific further molded Japanese submarine strategy. As American submarines sank Japanese merchant ships that were resupplying Pacific Ocean outposts, the Japanese struggled to replace those ships and the tonnage of cargo needed to keep those outposts operating. The Japanese sought to use submarines to fill the gap left by their wrecked merchant fleet. Thus, subs that were at one time conducting war patrols were now being taken off the line to move cargo to outposts.
In 1944, the three submarine squadrons under the Sixth Fleet became two squadrons; one squadron of coastal submarines and the other ocean-going, with a handful of submarine divisions and flotillas (smaller organizations than a squadron with 2 to 8 submarines each). In 1945, these units broke down further into one squadron of three high-speed submarines (I-200s) supported by a submarine tender, four submarine divisions (with 3 to 5 submarines each) with a Hunter-Killer Destroyer Squadron, and an aviation Patrol Squadron (VP).
The last notorious action of the Japanese submarine force occurred on July 30, 1945, when the I-58 attacked the USS Indianapolis (CA 35) on her way to Leyte Gulf after delivering some of the parts of the Atomic Bomb to Tinian in the Marianas. Because the Indianapolis was sailing alone and was unaware of the submarine, Commander Hashimoto Mochitsura, decided to use torpedoes instead of one of his manned suicide torpedoes called kaitens. Commander Hashimoto assumed because the Indianapolis was unaware of I-58 that she would not take evasive or anti-submarine action, and if he could use a standard torpedo, he could spare a kaiten pilot’s life. Just after midnight, the I-58 fired two Type 95 21-inch torpedoes; one hit at the bow and the other at amidships of the Indianapolis. Tragically, the Indianapolis was unable to send an SOS message, so her loss was unknown at the time of the sinking. After several days, no action was taken to look for survivors because the standard practice at the time was to not report a ship overdue and presumed lost. This exposed the surviving crew of almost 900 (out of 1,195) to the sea for four days. Through various means, the survivors dwindled from 900 to 316 until a search plane from Peleliu finally spotted the stricken sailors and started the rescue effort.
By the war’s end, the Japanese submarine force had been vastly reduced. The toll of the American submarine and bombing campaigns prevented the Japanese from adequately replacing any of their lost merchant ships, surface warships, and submarines. With what little resources they had, the Japanese constructed a large number of Type A submarines and Kaitens to thwart the inevitable invasion of Japan, and to support the remaining aircraft carrying submarines (I-400, I-401, I-13 and I-14) on a kamikaze strike on the American fleet at Ulithi.
The end of WWII also brought to light the war crimes that were committed at sea by some of the Japanese submarines. Submarine warfare is in itself horrific; ships were attacked without warning and any surviving crews were often left stranded in an unforgiving sea and exposed to the elements. While horrific, these realities were not considered war crimes. However, international law states that survivors of submarine attacks are to be either rescued or left to “the fate of the sea.” The murder of a stricken, shipwrecked crew is against law, but unforunately, at one time or another, all nations involved in World War II overstepped this rule. The commander of Submarine Division One, Captain Ariizumi Tatsunosuke, was one individual who perpetrated such war crimes under Japan’s flag. Serving aboard the I-401 in August 1945, he committed suicide after the submarine was captured at sea following the end of hostilities. The officers of rank aboard the I-401 attested to Captain Ariizumi’s dread of being captured and his fear of reprisal for the atrocities he committed as the commanding officer of the I-8 operating in the Indian Ocean. On several occasions after sinking an Allied ship, Ariizumi brought survivors aboard to put them through a gauntlet of humiliating acts and torture, only to be murdered afterwards at the hands of the submarine’s crew.
Ironically, the Japanese Submarine Force, which is not as well described in our histories of World War II, were active participants at the beginning and end of the Pacific War. Notably, the first and last Japanese warships sunk in World War II were submarines. On the morning of December 7, 1941, the Japanese sent into Pearl Harbor five Type A or midget submarines in addition to the air attacks. The midget submarines were carried by ocean-going submarines the I-16, I-18, I-20, I-22, and I-24. One of the Japanese midget submarines was seen following a barge heading into Pearl Harbor at around 6:37AM. The USS Ward (DD 139) fired at her and sank her a bit over an hour before the main attack on Pearl Harbor, and ironically the first shot of the Pacific War. The first Prisoner of War was Ensign. Kazuo Sakamaki, a crew member of the HA-19 midget submarine, that washed up on Bellows Beach, Hawai’i the morning of the attack. But the first warship lost by Japan after war was officially declared was the I-170, which was sunk by carrier based aircraft from the USS Enterprise (CV 6) on December 10, 1941. The first Japanese warship sunk by an American submarine was the I-173 on January 27, 1942, when the USS Gudgeon (SS 211) was returning to Pearl Harbor from her first war patrol. The last Japanese warship not categorized as a coastal defense vessel sunk by the United States in World War II was the I-373. It was sunk on August 14, 1945 by the USS Spikefish (SS 404). Much like their American counterparts, the Japanese Submarine Force was a silent service that rose to the surface during critical times during war as described in this brief overview. But unlike their American counterparts, researching this service arm of the Imperial Japanese Navy can be difficult in American records - unless you know how.
What resources are available at the National Archives to study Japanese submarines during World War II? The best Navy record groups to start with are Record Group 19: Records of the Bureau of Ships; Record Group 38: Records of the Chief of Naval Operations; Record Group 80: Records of the Department of the Navy; and Record Group 313: Records of Naval Operating Forces. There are also a few Army record groups that contain some information on Japanese submarines, including Record Group 153: Records of the Judge Advocate General (ARMY); Record Group 331: Records of Allied Operational and Occupation Headquarters, World War II in the records of the Supreme Commander, Allied Powers (SCAP); Record Group 493: Records of U.S. Army Forces in China-Burma-India Theaters of Operation; and Record Group 550: United States Army, Pacific (USARPAC).
In Record Group 19, the most useful group of records is the General Correspondence series for 1940-1945. This entry has been divided into several sub-entries based on their arrangement using the Navy Filing Manual (4th Edition, 1941). These records contain information about the material aspects of Japanese submarines, rather than operational records. The first filing designations suggested for exploring correspondence records are EF37 and EF74. EF is the Navy Filing Manual designation for a foriegn country, making EF37 the designation for Japan. EF74, on the other hand, was a designation that developed during the war to mean “captured enemy equipment.” These two designations paired with “SS”, the Navy Filing Manual designation for “submarines,” can be found in General Correspondence Filed Under Filing Classifications EA to EZ1, 1940 - 1945. The beginning filing designation to attempt would be EF37/SS or EF74/SS to find information on Japanese submarines or captured submarines, but it may not be all the information that is available because of the way that files were marked. Typically, you can flip a paired filing designation, so it is likely to find information under SS/EF37 and SS/EF74 as well, and those could be found under General Correspondence Filed Under Filing Classifications S1 to VZ, 1940 - 1945. As an adjunct to the General Correspondence, the Bulky Enclosures to the General Correspondence may also include additional textual materials and perhaps materials in other formats, such as drawings or photographs that were enclosures to the correspondence. While most of the evaluation of Japanese submarine technology was conducted in 1945, there was some testing done in 1946 as well as the final disposition of the submarines sunk off the coast of Japan or near Hawaii. Again, the filing designations EF37/SS or EF37 on its own will be places to look within the Confidential Correspondence, 1946.
The records in RG 19 are mostly post-war testing and evaluation of captured Japanese submarines with particular interest in enormous Sen Toku (I-400, I-401, and I-402) aircraft carrying submarines and the high submerged speed Sen Taka (I-201, I-202, and I-203). The latter class of submarine, the Sen Taka, was similar to the German Type XXI class submarine in that they used larger banks of high capacity batteries to drive the submarine at much higher speeds while submerged than their standard counterparts. These post-war files about the submarines are related to the U.S. Navy’s Technical Mission to Japan (NTMJ), which will be explored more later. These files also have information about what intelligence was being collected about Japanese submarines during the war. There is some information on the midget submarines that were captured after the attack on Pearl Harbor (December 1941) and the submarine attack on Sydney (June 1942).
Unfortunately, there are no historical representatives of these submarines outside of the wrecks found on the ocean floor off the coast of Japan and Hawaii. This is because the Western Allies were not willing to share these technological advances with the Soviet Union since the Soviet Union had only joined the Pacific War on August 6, 1945. Unlike their agreements to share captured German technology, the U.S. Navy and the Western Allies had more control over the captured materials in the Pacific, giving them a short period of time to make their evaluations of Japanese naval technology and dispose of it before the Soviet teams arrived. In the Spring of 1946 during Operation Road's End, most of the captured Japanese vessels were either scuttled or made into targets and sunk. There were a few submarines like some of the Sen Toku (I-401) and Sen Taka (I-203) that were spirited away to Hawaii for further evaluation and later sunk as targets.
There are some other series in RG 19 that relate to the evaluation of Japanese submarines. There is a series of Correspondence Relating to Captured Enemy Equipment, 1945 - 1952. This is a small series, and primarily about German naval technology, but there is a bit of Japanese and Italian naval technology too. A similar series, Records Relating to Foreign Ships and Ordnance and U.S. Countermeasures, ca. 1929 - 1948, contains information on Japanese ships, torpedoes, ordnance, suicide weapons, and submarines. This series includes copies of reports from the Naval Technical Mission to Japan, and from the United States Strategic Bombing Survey.
Record Group 38: Records of the Chief of Naval Operations has the lion’s share of records relating to Japanese submarine operations and how the U.S. Navy responded to them. In terms of operations of the Japanese Submarine Force, these series are good places to start: Records of the Japanese Navy, Microfilmed Seized Japanese Records, Intercepted Enemy Radio Traffic, Final Reports of the Naval Technical Mission to Japan, and Office of Naval Intelligence Monographs on Japanese Records.
As the name implies, the Records of the Japanese Navy is a series of files on the Japanese Navy collected by the U.S. Navy during and after World War II. This series includes unique records, as well as copies of records contained in other series mentioned in this section. There are interrogations, translations of captured records, technical bulletins and reports from the Army and Navy missions to Japan on the Japanese Navy, and information on Japanese ships, units, and other commands from different Allied resources. One of the unique items in this series is a detailed set of photographs of the inner workings of the HA-19 (listed in as I-19) when the U.S. Navy dissected her after her capture on December 7, 1941. These photographs are in Box 166A. There are post-war interviews with Japanese officials and commanders, some of which are duplicated in the Japanese Monographs that are in Record Group 550: Records of the U.S. Army, Pacific. In these monographs are discussions of the changing strategy of the Japanese Submarine Force.
The Seized Japanese Records are microfilmed copies of the records taken at the end of the war from the Japanese Naval Ministry. These records are largely untranslated and primarily in pre-war Japanese, which is a little different than current Japanese, though there are some translations with translator’s notes. For submarines, the primary section of this series is in Unit and Individual Ship Records from JD-37 to JD-39 (reel numbers), and there are some records of submarine tenders on JD-77. There may be additional information on submarine operations and submarine construction in other sections, such as in “Operations” where there are records of major battles like Midway and the Philippine Sea, or in “Naval and Guard District and Lesser Unit Records” where records of naval bases and shipyards are located.
The Intercepted Enemy Radio Traffic records are copies of decoded and translated messages of German and Japanese government, military, and naval coded messages. For the Japanese messages, there are segments that are broken down into government offices (Imperial Headquarters, Naval Section, Naval Ministry, and Naval General Staff); ship type commands including submarine squadrons and divisions; high naval commands, including Combined Fleet and number fleets including the Sixth Fleet and Japanese Submarine Command; specific ships by hull designation I, RO, and HA; personalities; and place names. In the specific ship files, there are sometimes index cards or memos from the Office of Naval Intelligence about those ships and their fate.
There are several entries related to what the Office of Naval Intelligence (ONI) collected on the Japanese Navy and their submarine forces with the primary series of the Japanese Monographs. In general, the Monograph files for Japan and other places are like library vertical files where ONI put interesting things about subjects related to a particular country and subject. These files have their own unique filing system that is apart from the Navy Filing Manual. The system is based on divisions along the hundreds and then subdivisions in thousands (###-#### or 912-0079). Under the prefixes 900 to 999 are Navy related subjects. For Japanese submarines, the filing designation is “912” for “Ships” and “-1000” for submarines for the designation of 912-1000. Similarly for naval operations can be found under “915” for “Operations,” there may be additional material because it includes cooperation with Germany, in which many things were transported by submarine. Specifically for submarine operations or naval battles that included submarines, they can be found under 915-0700. There are also ONI Monograph Files for the Pacific Ocean Areas (POA) including the Japanese Mandate Islands and Netherland East Indies (NEI). These files use the same system of organization.
Information on the ONI Monographs, Naval Attache Intelligence Reports, can be found at the Archives.gov. Additionally, there is a microfilm series (M1332) which serves as the index to the reports. In these files are technical reports and descriptions of Japanese submarine activity from the naval attaches in Allied countries. In particular, there are reports from the Australians and the Dutch as they recorded their encounters with and attacks by the Japanese.
In addition to the materials described above, which are about Japanese submarines, submarine warfare doctrine, and Japanese submarine operations, we also have records from the perspective of the targeted naval and merchant ships of the US and Allied Forces. Researching this kind of topic will require knowing the places, dates, and units attacked by the Japanese or responding to a Japanese submarine attack. Record series in RG 38, including the World War II Command Files and the World War II Action and Other Operational Reports, are arranged by hierarchy of naval command. You may need to look at not only a specific ship’s records, but also some general records like Anti-Submarine Warfare (ASW) Bulletins for a particular period to begin developing the framework of a story.
There are other series in RG 38 which have their own indices like Flag File Select Document Files and Index to Flag File Select Documents and 10th Fleet Records ASW Incident Reports. The File Flag Select Document series is a hodge-podge of records similar in nature to the World War II Command Files, but not as organized. In the index, you can find topics on midget submarines and giant I-400s. In the ASW Incident reports, in which the index is arranged by the attacking unit on the submarine, there may be duplicate reports found in the action reports. The purpose of these reports was to create a data set of practices in ASW tactics by those who have experience.
Submarine warfare was a horrible experience for the target ships. The strikes came without warning and the mariners’ lives were turned upside down. In most cases, the belligerents in World War II observed international law regarding survivors of a sunken ship, which stated that no further action should be taken against survivors of a sunken ship. However, there were a few submarine commanders who committed atrocities on the high seas. You can begin research on this subject with the 10th Fleet Records Allied Shipping Losses, which are reports of sunken ships that sometimes includes action reports and survivor statements in addition to the material records on the ship. From these records, the crews of ships that were harassed, captured or executed can be researched in the U.S. Army’s Judge Advocate General’s Records relating to Japanese War Crimes in RG 153. There are two indices to these records, the Name Index and the Place Index. Within the place index, there is a portion that lists names of ships. These could be ships that were attacked and the crews harassed or executed, or they may be Japanese ships transporting prisoners of war (POWs) in poor conditions, which were also known as “Hell Ships.” The indices have information to pull the War Crime Case Files. Many of the Japanese wartime atrocities conducted at sea were conducted in the Indian Ocean on ships going from the Suez Canal to the China, Burma, India (CBI) Theater. There could be some additional information in Record Group 493: Records of the U.S. Army Forces in the China, Burma, India Theater.
For information regarding textual records on Japanese submarines, Japanese submarine doctrine, and Japanese submarine operations, please contact archives2reference@nara.gov.
In addition to the textual records assets, there are also special media records that relate to Japanese submarines. In the Still Photographs Branch, there are photographs of Japanese ships and submarines in several record groups. Photographs have special designations using record group numbers and specific collections designated by a letter or letters. Some of the larger collections of photographs that include Japanese submarines are RG 19 under 19-NN and 19-LCM; Record Group 26: Records of the U.S. Coast Guard under 26-G; RG 38 under 38-JS; Record Group 80: Records of the Department of the Navy under 80-G; Record Group 111: Records of the U.S. Army Signal Corps under 111-SC; and Record Group 208: Records of the Office of War Information (OWI) under 208-AA and 208-MO. In the back of the Still Photographs Reading Room at College Park are a series of card catalogs; from right to left of the room are indices to RG 19, RG 80, and RG 111 where you can search under different topics, be it generally under Japanese submarines or specific boats like the I-58.
For more information on photographs of Japanese submarines or other World War II photographs, please contact stillpix@nara.gov.
In the Cartographic Branch, there are two collections of Japanese ship drawings: Captured Japanese Ship Plans and Design Data, 1946 - 1947 in Record Group 19 and for some older boats that survived to World War II, Plans of Japanese-Built Ships, 1919 - 1934 in Record Group 32: Records of the U.S. Shipping Board. The Captured Plans are on microfilm on ten reels of National Archives Publication M1176 and the plans are arranged by enclosure number. The Plans of Japanese Built Ships are arranged alphabetically by English (or Romanji) names of the ships. For more information on captured drawings of Japanese naval vessels, please contact branch.cartographic@nara.gov.