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Submarine forces of the Imperial Japanese Navy
Imperial Japanese Navy submarines originated with the purchase of five Holland type submarines from the United States in 1904. Japanese submarine forces progressively built up strength and expertise, becoming by the beginning of World War II one of the world's most varied and powerful submarine fleets.

The Imperial Japanese Navy (IJN) acquired its first submarines during the Russo Japanese War on 12 December 1904 where they arrived in sections at the Yokohama dockyards. The vessels were purchased from the relatively new American company, Electric Boat, and were fully assembled and ready for combat operations by August 1905. However, hostilities with Russia were nearing its end by that date, and no submarines saw action during the war. The submarines that Electric Boat sold to Japan were based on the Holland designs, known as Holland Type VIIs similar to the American s. The five imported Hollands were originally built at Fore River Ship and Engine Company in Quincy, Massachusetts and this submarine was preserved as a memorial in Kure until the end of World War II. torpedo). Overall, despite their advanced technical innovation, Japanese submarines were built in relatively small numbers, and had less effect on the war than those of the other major navies. The IJN pursued the doctrine of guerre d'escadre (fleet vs fleet warfare), and consequently submarines were often used in offensive roles against warships. Warships were more difficult to attack and sink than merchant ships, however, because naval vessels were faster, more maneuverable, and better defended. The IJN submarine arm did have a number of notable successes against American warships, however. During the Battle of Midway, Japanese submarine I 168 administered the final coup de grace that sank the fleet carrier Yorktown, as well as sinking the destroyer Hammann. A few months later, on September 15, 1942, with a single salvo of torpedoes, Japanese submarine Japanese submarine I 19 sank the fleet carrier Wasp and damaged both the battleship North Carolina and the destroyer O'Brien. On November 13, 1942, the submarine Japanese submarine I 26 torpedoed and sank the anti aircraft cruiser Juneau, and a year later on November 23, 1943, the submarine Japanese submarine I 175 torpedoed and sank the escort carrier Liscome Bay, both with heavy loss of life. The Japanese submarine I 176 had the distinction of both severely damaging the heavy cruiser Chester, knocking her out of the war for a year, on October 20, 1942, and of also sinking Corvina (the only American submarine to be sunk by a Japanese submarine in the entire war) on November 16, 1943. Twice in the first year of the war, Japanese submarines torpedoed the aircraft carrier Saratoga, and, while not sinking her, put her in the repair yard at a time when the US Navy could ill afford to do without her. Saratoga was torpedoed by submarine Japanese submarine I 6 on January 11, 1942, putting her out of action and unavailable to participate in the desperate carrier battles and raids of the next five months, and then hit again three months after her return on September 1, 1942, by Japanese submarine I 26, which put her out of action for another eleven weeks in the middle of the intensely engaged land air sea battles of the Guadalcanal Campaign. A plane launched from one of the innovative aircraft carrying submarines, Japanese submarine I 25, conducted what remains the only ever aerial bombing attack on the continental United States, when Warrant Flying Officer Nobuo Fujita piloting a Yokosuka E14Y scouting plane dropped four 168 pound bombs in an attempt to start forest fires outside the town of Brookings, Oregon, on September 9, 1942. Earlier in the year, in February 1942, the submarine Japanese submarine I 17 fired a number of shells from her deck gun at the Elwood Oil Fields near Santa Barbara, California. None of the shells caused any serious damage. However, as fuel oil diminished and air superiority was lost, Imperial submarines were no longer able to continue with such successes. Once the United States was able to increase its production of destroyers and destroyer escorts, as well as bringing over highly effective anti submarine techniques learned during the Battle of the Atlantic, they continually took more and more of a toll on Imperial Japanese submarines, which also tended to be not as deeply diving as their Kriegsmarine counterparts. Accordingly, the Japanese submarine arm had few notable successes against Allied warships during the final two years of the war. One victory was the Japanese submarine I 41 knocking the anti aircraft cruiser Reno out for the rest of the war with a torpedo hit on November 3, 1944 (this was the first time in almost two years that a Japanese submarine had successfully attacked an Allied ship operating with a fast carrier task force). A more famous incident was the Japanese submarine I 58 torpedoing and sinking heavy cruiser Indianapolis, with heavy loss of life. The sinking occurred on July 30, 1945, just two weeks before the Japanese surrender, at a time when few in the United States Navy expected continued Japanese submarine attacks. The Imperial Japanese Navy's doctrine of fleet warfare (guerre d'escadre) resulted in its submarines seldom posing a threat to allied merchant convoys and shipping lanes to the degree that the Kriegsmarine's U boats did as they pursued commerce raiding against Allied and neutral merchant ships. During the war, IJN submarines did sink about 1 million tons (GRT) of merchant shipping (184 ships) in the Pacific; by contrast U. S. Navy submarines sank 5.2 million tons (1,314 ships) in the same period, while U boats of Nazi Germany's Kriegsmarine, the IJN's Axis partner, sank 14.3 million tons (2,840 ships) in the Atlantic and other oceans. During the last two years of the War in the Pacific, many IJN submarines were also occupied serving to transport supplies to isolated island garrisons, ones that had been deliberately bypassed by the Americans and the Australians and which could not be reached by surface transports because of blockade by Allied warplanes and naval vessels. Early models of IJN submarines were relatively less maneuverable under water, could not dive very deeply, and lacked radar. (Later in the war units that were fitted with radar were in some instances sunk due to the ability of American radar sets to detect their emissions. For example, Batfish sank three such IJN submarines near Japan in just four days). After the end of the conflict, several of Japan's most innovative and advanced submarines were sent to Hawaii for inspection in "Operation Road's End" (, I 401, , and I 203) before being scuttled by the U. S. Navy in 1946 when the Soviet Union demanded access to the IJN submarines.

The Japanese applied the concept of the "submarine aircraft carrier" extensively, starting with the J3 type of 1937–38. Altogether 41 submarines were built with the capability to carry seaplanes. Most IJN submarine aircraft carriers could carry only one aircraft, but I 14 had hangar space for two, and the giant , three.

Yanagi missions were enabled under the Axis Powers' Tripartite Pact to provide for an exchange of strategic materials and manufactured goods between Germany, Italy and Japan. Initially, cargo ships made the exchanges, but when this was no longer possible, submarines were used. Only six submarines attempted this trans oceanic voyage during World War II: Japanese submarine I 30 (mid June to August 1942), Japanese submarine I 8 (June 1943), Japanese submarine I 34 (October 1943), Japanese submarine I 29 (November 1943), and German submarines German submarine U 511 (August 1943) and German submarine U 864 (December 1944). Of these, I 30 was partially successful but was later sunk by a mine, I 8 completed her mission, I 34 was sunk by British submarine , and I 29 by the United States submarine, Sawfish (assisted by Ultra intelligence). Japanese submarine I 52 made the final attempt.

This class includes the largest of Japanese submarines, characterized by great size and range.

The Kaidai I type (海大I型) (I 51 class) submarine was the prototype for the types (KD2 KD7) that followed and was based on the German cruiser submarine and the British L class submarine. Japanese submarine I 51 – scrapped 1941.

The Kaidai II type (海大II型) (I 152 class) submarine was based on U 139 and the British K class submarine. I 52/Japanese submarine I 152 – scrapped 1946–1948.

The Kaidai IIIa type (海大IIIa型) (I 153 class) submarines were similar to the Type KD1 and KD2 but with strengthened hulls. In 1945, I 155 and I 158 were modified as Kaiten suicide torpedo carriers, each armed with two kaitens. Japanese submarine I 53/I 153 – sank Ben 2 on 20 February in the Indian Ocean, in the Bali Strait on 27 February 1942 and off Java on 28 February 1942. I 153 herself was sunk as a target in the Seto Island Sea on 8 May 1946 as part of Operation Bottom. Japanese submarine I 54/I 154 – scuttled in the Seto Island Sea in May 1946. Japanese submarine I 55/I 155 – sank off Java on 7 February 1942 and in the Java Sea on February 13, 1942. I 155 herself surrendered 2 September 1945 and was scuttled in the Seto Island Sea in May 1946. I 58/Japanese submarine I 158 – sank in the Java Sea on 3 January 1942, off Bawean Island on 9 January 1942, between Tjilatjap and Padang on 22 February 1942 and south of the Sunda Strait on 25 February 1942. I 158 herself surrendered on 2 September 1945 and was scuttled off the Gotō Islands on 1 April 1946.

The Kaidai IIIb type (海大IIIb型) (I 156 class) submarines were similar to the Type KD3a but were 16 inches longer and had a different bow shape. I 56/Japanese submarine I 156 – sank five merchant ships. I 156 surrendered on 2 September 1945 and was scuttled off the Gotō Islands on 1 April 1946 by Nereus as part of Operation Road's End. I 57/Japanese submarine I 157 – sank SS Djirak on 7 January 1942. I 157 surrendered on 2 September 1945 and scuttled off the Gotō Islands on 1 April 1946 by Nereus as part of Operation Road's End. I 59/Japanese submarine I 159 – sank off Sumatra on March 1, 1942. I 159 surrendered on September 2, 1945, and sunk as a target off the Gotō Islands on 1 April 1946. Japanese submarine I 60 – Accidentally rammed I 63 off Mizunoko Light on 2 February 1939. I 60 herself was sunk off Kratakoa Island on 17 January 1942 by Japanese submarine I 63 – Accidentally rammed by I 60 off Mizunoko Light on 2 February 1939. Refloated January 1940 and then scrapped.

The Kaidai IV type (海大IV型) (I 61/I 162 class) submarines were slightly smaller and had four torpedo tubes, but were otherwise similar to the Type KD3. Japanese submarine I 61 – Sunk in collision with gunboat Japanese gunboat Kiso Maru in Koshiki Channel on 2 October 1941. Refloated in early 1942 and sold for scrap. I 62/Japanese submarine I 162 – Sank Mikoyan on 3 October 1942, Manon on 7 October 1942 and Fort McCloud on 22 February 1944. The I 162 herself surrendered on 2 September 1945 and scuttled off the Gotō Islands on 1 April 1946 by Nereus as part of Operation Road's End. Japanese submarine I 64/I 164 – Sunk off Cape Ashizuri on 17 May 1942 by Triton.

The Kaidai V type (海大V型) (I 165 class) submarines were similar to the Type KD4 but had an improved operating depth. I 65/Japanese submarine I 165 – Depth charged off Saipan on 27 June 1945 by a US Navy patrol bomber of VPB 142. I 66/Japanese submarine I 166 – Sunk off One Fathom Bank on 17 July 1944 by Japanese submarine I 67 – Sank in diving accident off Minamitorishima on 29 August 1940.

The Kaidai VIa type (海大VIa型) (I 168 class) submarines were similar to the KD5 but with a higher speed. I 68/Japanese submarine I 168 – Sunk in the Steffen Strait on 27 July 1943 by Scamp. I 69/Japanese submarine I 169 – Sank in diving accident in Truk Lagoon on 4 April 1944. Japanese submarine I 70 – Sunk by a Douglas SBD Dauntless aircraft from VS 6 (Enterprise) on 10 December 1941. This was the first enemy combatant ship sunk by U. S. forces. I 71/Japanese submarine I 171 – Depth charged off Buka Island on 1 February 1944 by Guest and Hudson. Japanese submarine I 72/I 172 – Missing after 28 October 1942. Possibly depth charged off San Cristóbal by McCalla on 3 November 1942. Japanese submarine I 73 – Sunk by Gudgeon on 27 January 1942. I 73 was the first warship sunk by a US Navy submarine.

The Kaidai VIb type (海大VIb型) (I 174 class) submarines were similar to the KD6a but were one foot longer and 25 tons heavier. Japanese submarine I 174 – sunk off Truk on 12 April 1944 by aircraft from VB 108. Japanese submarine I 175 – sunk off Wotje Atoll on 17 February 1944 by Nicholas.

The Kaidai VII type (海大VII型) or Shin Kaidai type (新海大型) (I 176 class) submarines were similar to the KD6 but with the torpedo tubes moved forward and a slightly improved operating depth. I 76/Japanese submarine I 176 – sank Corvina patrolling off Truk on 16 November 1943, the only known Japanese submarine success against a US submarine – Snook was a probable second victim by Japanese submarines. I 176 was lost a year later off Buka Island on 16 May 1944, depth charged by Franks, Haggard, and Johnston. Japanese submarine I 177 – Sank AHS Centaur off Australia on 14 May 1943. The I 177 herself is sunk by Samuel S. Miles on 3 October 1944. I 78/Japanese submarine I 178 – Missing after 17 June 1943. Possibly sunk 25 August 1943 near the Solomon Islands by Patterson. I 79/Japanese submarine I 179 – Sank during sea trials in the Seto Island Sea on 14 July 1943. Salvaged 1956 1957 and then scrapped. I 80/Japanese submarine I 180 – Sunk off Chirikof Island on 27 April 1944 by Gilmore. I 81/Japanese submarine I 181 – Ran aground and sunk in Kelanoa Harbour on 16 January 1944. I 82/Japanese submarine I 182 – Sunk off the New Hebrides on 1 September 1943 by Wadsworth. I 83/Japanese submarine I 183 – Sunk near the Bondo Strait on 29 April 1944 by Pogy. I 84/Japanese submarine I 184 – Sunk near Saipan on 19 June 1944 by a torpedo bomber from Suwanee. I 85/Japanese submarine I 185 – Sunk near Saipan on 22 June 1944 by Newcomb and Chandler.

The Junsen I type (巡潜I型) (I 1 class) submarines were based on the Kaidai II (Type KD2) and German submarine Japanese submarine I 1 – sank off Western Australia on March 3, 1942. I 1 herself was attacked by and ran aground on Fish Reef January 29, 1943; valuable codes and code books from the wreck are salvaged by Allied forces. Japanese submarine I 2 – sank HMS Nam Yong off Christmas Island on February 28, 1942, and in the Indian Ocean on March 1, 1942. I 2 herself was sunk in the Bismarck Sea on April 7, 1944, by Saufley. Japanese submarine I 3 – sunk December 9, 1942 near Kamimbo Bay by PT 59. Japanese submarine I 4 – sank Høegh Merchant off Oahu December 14, 1941, Ban Ho Guan off Bali February 28, 1942 and USS Washingtonian off Eight Degree Channel April 6, 1942. I 4 herself was sunk in St. George's Channel on December 21, 1942, by Seadragon.

The Junsen I Modified type (巡潜I型改) (I 5 class) submarine was similar to the Type J1, but with facilities for one aircraft. Japanese submarine I 5 – possibly sunk 19 July 1944 off Guam by Wyman.

The Junsen II type (巡潜II型) (I 6 class) submarine was similar to the I 5 class, but with a catapult for aircraft. Japanese submarine I 6 – sank Clan Ross in the Arabian Sea on April 2, 1942, and Bahadur in the Arabian Sea on April 7, 1942. I 6 herself was accidentally rammed and sunk 16 June 1944 off Hachijō jima by Toyokawa Maru.

The Junsen III type (巡潜III型) (I 7 class) submarines combined the benefits of the Type J2 and the Kaidai V (KD5). This type later led to the Type A, Type B, and Type C submarines. Japanese submarine I 7 – sank Merkus off Cocos Island on March 4, 1942, Glenshiel in the Indian Ocean on April 3, 1942, and USS Arcata off Unalaska on July 14, 1942. I 7 herself was damaged by gunfire off Kiska June 22, 1943 from Monaghan and ran aground on the Twin Rocks. I 7 was scuttled on June 23. Japanese submarine I 8 – sank Tjisalak on March 26, 1944, in the Indian Ocean and Jean Nicolet in May 1944. I 8 herself is sunk off Okinawa on March 31, 1945, by Morrison.

The Type A or Junsen A type (甲型 or 巡潜甲型) (I 9 class) submarines were large seaplane carrying submarines, with communication facilities to allow them to operate as command ships for groups of submarines. The type was also equipped with a hangar for one aircraft. Japanese submarine I 9 – sunk June 14, 1943 off Kiska by Frazier. Japanese submarine I 10 – sunk July 4, 1944 off Saipan by David W. Taylor and Riddle. Japanese submarine I 11 – missing south of Funafuti after January 11, 1944. The I 11 probably struck a mine laid by Terror.

The Type A Modified 1 or Junsen A Modified 1 type (甲型改1 or 巡潜甲型改1) (I 12 class) submarine was similar to the Type A1, but with less powerful engines, giving the type slower surface speed but a longer range. Japanese submarine I 12 – sunk November 13, 1944 by Ardent and Rockford.

The Type A Modified 2 or Junsen A Modified 2 type (甲型改2 or 巡潜甲型改2) (Type AM (A Modified), I 13 class) submarines was a large seaplane carrying submarine, with hangar space for two aircraft. These giant submarines were originally of the A2 type, but following the cancellation of a number of I 400 class submarines, their design was revised after construction started to carry a second aircraft. The seaplanes were to be the Aichi M6A1 bomber carrying 800 kg bombs. The range and speed of these submarines was remarkable, at , but their underwater performance was compromised, making them easy targets. Japanese submarine I 13 — Sunk 16 July 1945 by Lawrence C. Taylor and aircraft from Anzio about 550 mile (885 km) east of Yokosuka. Japanese submarine I 14 – Surrendered 27 August 1945. Sunk as target 28 May 1946 off Oahu, Hawaii, in 2600 feet (792 m) of water by Bugara. Wreck found in 2009.

The Type B Modified 1 or Junsen B Modified 1 type (乙型改1 or 巡潜乙型改1) (I 40 class) submarines were externally similar to the Type B1, but with a high tensile strength steel hull and diesel engines of a simpler design. In 1944, I 44 was modified as a Kaiten suicide torpedo carrier, armed with six kaitens. Japanese submarine I 40 – Missing off the Gilbert Islands after 22 November 1943. Japanese submarine I 41 – Sunk 18 November 1944 by Lawrence C. Taylor. Japanese submarine I 42 – Sunk 23 March 1944 by Tunny. Japanese submarine I 43 – Sunk 15 February 1944 by Aspro. Japanese submarine I 44 – Missing off Okinawa after 4 April 1945. Possibly sunk off Okinawa by a TBM Avenger of VC 92 on 29 April 1945. Japanese submarine I 45 – Sunk 29 October 1944 by Whitehurst.

Eighteen of the twenty one Type B Modified 2 or Junsen B Modified 2 type (乙型改2 or 巡潜乙型改2) (I 54 class) submarines were cancelled in 1943 in favor of the Type E submarine, leaving the I 54, I 56, and I 58. In 1944, I 56 and I 58 were modified as Kaiten suicide torpedo carriers, each armed with four kaitens. Japanese submarine I 54 – Missing off Leyte after 23 October 1944. Possibly sunk 28 October 1944 by Gridley and Helm. Japanese submarine I 56 – Possibly sank Snook sometime after 8 April 1945. I 56 was herself later sunk 18 April 1945 by Collett. Japanese submarine I 58 – Sank Indianapolis on 30 July 1945. I 58 surrendered on 2 September 1945, and scuttled off the Gotō Islands on 1 April 1946 as part of Operation Road's End. The wreckage of I 58 was found in 2017.

The Type C or Junsen C type (丙型 or 巡潜丙型) (I 16 class) submarines were based on the Junsen type submarine and developed from the Type KD6. This type, like the other Type C submarines, was utilized as mother ships for the Kō hyōteki midget submarines and the Kaiten suicide torpedoes. Japanese submarine I 16 – Sank Susak on 6 June 1942, Aghious Georgios on 8 June 1942, Supetar on 12 June 1942, and Eknaren on 1 July 1942. Sunk 19 May 1944 by England. Japanese submarine I 18 – Sank Wilford on 8 June 1942, Mundra on 2 July 1942, and De Weert on 3 July 1942. Sunk 11 February 1943 by Fletcher. Japanese submarine I 20 – Sank Johnstown on 5 June 1942, Christos Markettos on 8 June 1942, Mahronda on 11 June 1942, Hellenic Trader and Clifton Hall on 12 June 1942, Goviken on 29 June 1942, and Steaua Romana on 30 June 1942. Missing after 31 August 1943, probably sunk either on 1 September 1943 by Wadsworth or on 3 September 1943 by Ellet. Japanese submarine I 22 – Sunk 6 October 1942 by a U. S. Navy PBY Catalina. Japanese submarine I 24 – Sank on 3 June 1942. Rammed and sunk 11 June 1943 by PC 487.

The Type C or Junsen C type latter batch (丙型 or 巡潜丙型 (後期型)) (I 46 subclass) submarines were nearly identical to the Type C1 with the exception that the Type C2 lacked the capability to carry the midget submarines. I 47 and I 48 were converted to carry kaiten manned suicide attack torpedoes. Japanese submarine I 46 – Missing after 26 October 1944. Possibly sunk by Gridley and Helm on 28 October 1944. Also reported sunk by a multi destroyer gun action involving Saufley, Renshaw, Waller, and Pringle around 28 November 1944. Japanese submarine I 47 – Sank Mississinewa on 20 November 1944. I 47 surrendered on 2 September 1945 and was scuttled off the Gotō Islands on 1 April 1946 as part of Operation Road's End. The wreck of I 47 was found in 2017. Japanese submarine I 48 – Sunk January 23, 1945 by Conklin.

The Type C Modified or Junsen C Modified type (丙型改 or 巡潜丙型改) submarines (I 52 class) were submarines of the Imperial Japanese Navy, designed and built by Mitsubishi Corporation, between 1943 and 1944, as cargo carriers. They were quite long and carried a crew of up to 94 officers and enlisted. They also had a long cruising range at a speed of The Japanese constructed only three of these during World War II (Japanese submarine I 52, Japanese submarine I 53 and Japanese submarine I 55), although twenty were planned. They were among the largest submarines ever built to date, and were known as the most advanced submarines of the period. I 53 was converted to carry kaiten manned suicide attack torpedoes. Japanese submarine I 52 – Sunk during Yanagi (exchange) mission to Germany on 24 June 1944 by aircraft from Bogue southwest of the Azores. She was carrying Japanese engineers and a cargo of rubber, gold, and quinine to Germany. Japanese submarine I 53 – Sank Underhill on 24 July 1945. I 53 surrendered on 2 September 1945 and sunk as a target off the Gotō Islands on 1 April 1946 by Nereus as part of Operation Road's End. The wreck of the I 53 was found in 2017. Japanese submarine I 55 – Missing after 13 July 1944. Possibly sunk by William C. Miller on 14 July 1944. Sinking also credited to Reynolds and Wyman on 28 July 1944.

The Type D ((潜)丁型) or Sen'yu( Dai) type (潜輸(大)型) (I 361 class) and Sen'yu Modified type (潜輸改) (I 372 class) submarines were based on the U 155. This type was designed as transport submarines with torpedoes for self defense. Five of the submarines — I 361, I 363, I 366, I 367, and I 370 — were later modified to serve as kaiten suicide attack torpedo carriers, each armed with five kaitens. Japanese submarine I 361 – Sunk southeast of Okinawa on 31 May 1945, by aircraft from Anzio. Japanese submarine I 362 – Sunk in eastern Caroline Islands on 14 January 1945, by Fleming. Japanese submarine I 363 – Sunk by mine off Miyazaki on 29 October 1945. Salvaged and scrapped on 26 January 1966. Japanese submarine I 364 – Sunk east of Honshu on 16 September 1944, by Sea Devil. Japanese submarine I 365 – Sunk southeast of Yokosuka on 29 November 1944, by Scabbardfish. Japanese submarine I 366 – Blown up and scuttled off the Gotō Islands on 1 April 1946 as part of Operation Road's End. Japanese submarine I 367 – Blown up and scuttled off the Gotō Islands on 1 April 1946 as part of Operation Road's End. Japanese submarine I 368 – Sunk west of Iwo Jima on 26 February 1945, by aircraft from Anzio. Japanese submarine I 369 – Surrendered on 30 August 1945 and scrapped at Yokosuka in 1946. Japanese submarine I 370 – Sunk near Iwo Jima on 26 February 1945, by Finnegan. Japanese submarine I 371 – Sunk in Bungo Strait on 24 February 1945, by Lagarto. Japanese submarine I 372 – Sunk at Yokosuka on 18 July 1945, by aircraft from Task Force 38.

The Type D Modified ((潜)丁型改) (I 373 class) submarine was designed as a tanker submarine based on the Type D1 but with no torpedoes. Japanese submarine I 373 – sunk in the East China Sea on August 14, 1945, by Spikefish. I 373 was the last Japanese submarine sunk in World War II.

The Kiraisen type (機雷潜型) (I 121 class), the only Japanese minelayer submarines, were near copies of the World War I German minelayer submarine UB 125. Originally numbered I 21, I 22, I 23, and I 24, they were renumbered I 121, I 122, I 123, and I 124, respectively, in 1938. This type saw front line service during the Second Sino Japanese War and the first half of World War II, modified to add seaplane refueling to their capabilities, but surviving units were relegated to training duties in September 1943 due to their growing obsolescence. I 21/Japanese submarine I 121 – Surrendered in September 1945 and scuttled in Wakasa Bay along with Ro 68 and Ro 500 on 30 April 1946. Wreck found in 2018. I 22/Japanese submarine I 122 – Sunk in the Sea of Japan 9 June 1945 by Skate. I 23/Japanese submarine I 123 – Sunk off Savo Island 29 August 1942 by Gamble. I 24/Japanese submarine I 124 – Sank Hareldawns off Luzon on 10 December 1941. Sunk off Darwin 20 January 1942 by I 124 was the first IJN warship sunk by the Royal Australian Navy.

The Senho type (潜補型) (I 351 class) was a tanker/transport submarine. Japanese submarine I 351 – sunk July 14, 1945 in the South China Sea by Bluefish.

The Sentoku type (潜特型) (I 400 class) displaced 5,223 tons surfaced and measured 400 feet (122 m) overall. They had a figure eight hull shape for additional strength to handle the on deck hangar for housing the three Seiran aircraft. In addition, they had four anti aircraft guns, a large deck gun as well as eight torpedo tubes from which they could fire the Type 95 torpedo. Three of the Sentoku were built (Japanese submarine I 400, Japanese submarine I 401, and Japanese submarine I 402). Each had four engines and range at
Japanese submarine Ro 1 – Stricken 1932. Japanese submarine Ro 2 – Stricken 1932.