(I-8 by Takeshi Yuki scanned from "Color Paintings of Japanese Warships")

Stories and Battle Histories of the IJN's Midget Submarines

1 June 2018

By Bob Hackett and Sander Kingsepp

Discussion & Questions

Kure. In 1934, the IJN constructed her first two prototype midget submarines, capable of the amazing speed of almost 25 knots underwater. The new weapon was intended to be used in the future decisive battle, firing their torpedoes at enemy’s battle line from point-blank range. Initially, midget submarines were to be carried into the battle area by tenders (CHITOSE, CHIYODA, MIZUHO and NISSHIN), each embarking a dozen craft. Given their vital purpose, midget submarines were known under a bewildering variety of cover designations, such as Type A improved ASW target (Ko-Hyoteki), "special storage tubes" (Tokugata Kakuno-to) or simply "pipes" or "tubes".

Ko Gata (Type A) class midgets were powered by an electric motor, but were incapable of recharging their batteries. Initially, they were completed at Karasu-Kojima Torpedo Factory, but in fall 1942 production was transferred to Ourazaki on Kurahashi Jima, a small island about 12 miles S of Kure. More than twenty Type A's, including a few three-man training boats, had been completed before Pearl Harbor.

The last A type midget (HA-53) was completed in May 1943 as the Otsu Gata (Type B ) prototype. Later, HA-49 through HA-52 were rebuilt as Type B midgets. The Type B midgets were designed to overcome the shortcomings of the Type A midgets. They were equipped with a diesel generator (a converted tank engine) to recharge their batteries while running on the surface. This change tripled the range of the Ko-Hyoteki.

Subsequent production models were designated Hei Gata (Type C). This group was numbered HA-54-100. HA-54 was completed in Jan '44 and HA-100 in Aug '44. Some ten were converted to training boats.

Koryu (Type D) Tei Gata midget submarines were equipped with more powerful diesels and electric motors and could recharge their batteries faster. These changes again tripled their range. They were four feet longer and weighed 60 tons. Designed power underwater was 600 shp, but on most boats it was limited to 500 shp as a result of shortage of batteries. The crew was increased to five men, but the lack of bunk space for the crew limited her practical endurance to only three days. The first Type D, HA-101, was completed in May '44 and accepted into service on 28 May 1945. By war's end, 115 were completed and another 496 hulls were in various stages of construction. At least five Type D's were lost in operations at Okinawa in March 1945.

Kairyu (Sea Dragon) (aka SS Kanamono or Metal fitting Type SS) midget submarines. Kairyu was an independent design envisaged in early 1943 as a fast two-man "glider" submarine with small diving planes on both sides. It was "piloted” by a stick, just like an aircraft. The original version carried two 17.7-inch (45-cm) torpedoes mounted externally amidships. Most Kairyus were converted into suicide craft, carrying a 1,320 lb. (600-kg) warhead in the nose. Two prototypes were completed at Yokosuka in 1944. In February 1944, production began at eleven separate facilities, but was hampered by material shortages. By war's end, 224 of a planned 760 boats had been completed, most at Yokosuka and Uraga Dock in Tokyo and at Fujinagata in Osaka. None went on operational missions.

Kaiten were designed as tokko (suicide) weapons. They were based on Type 93 "Long Lance" oxygen propelled torpedoes. This page will not cover the operations of kaiten as coverage already exists within the TROMs of their mother submarines.

No detailed production records of the Ko-Hyoteki or Koryu (Scaly Dragon) midget submarines to include the dates laid down, launched and completed have been located, and may not exist. Similarly, records of individual midget submarines are incomplete as are the names of their crew members; however, Japanese and Allied records do contain some information concerning midget submarines' operations.

As a result of the foregoing, we cannot present midget submarines data in our usual Tabular Record of Movement (TROM) format; rather we have chosen to present the information by geographical areas of operation and time periods as listed below. This coverage will include known information on the following midget submarines:

Type A: HA-5, 8, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 21, 22, 23?, 28, 29, 30, 31, 32, 33, 34, 37, 38
Type A/B: HA-49, 50, 51?, 52, 53
Type C: HA-58, HA-60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 71, 73, 75, 76, 78, 79, 81, 82, 83, 84, 86
Type D: HA-204, 207, 208, 209, 210

For convenience, we have adopted the HA-type numeration to show the hull numbers of pertinent midget submarines. This system was not used by the IJN. In case of submarine-carried midgets with unknown hull numbers the "mother" submarine derived system is used instead (e.g. M-16 marks a midget carried by submarine I-16).

Pearl Harbor, Hawaii, 1941 (revised 9/1/17)

Sydney, Australia, 1942 (revised 3/1/18)

Diego Suarez, Madagascar, 1942 (revised 3/12/08)

Midway, 1942 (posted 6/23/06)

Solomon Islands, 1942 (revised 4/7/2012)

Kiska, Aleutians, 1942-1943 (posted7/31/06)

Bismarcks, 1943-1944 (revised 1/5/13)

Philippines, 1944-1945 (revised 7/1/13)

Marianas, 1944 (revised 12/23/09)

Halmahera, Moluccas, 1944 (posted 10/15/11)

Chichi-jima, Ogasawara (Bonin) Islands, 1944-1945 (posted 10/22/11)

Okinawa and the Ryukyu Islands, 1944-1945 (posted 1/5/07)

Japan and Operation "Downfall", 1945 (revised 6/1/18)

Bibliography of Sources

About the Authors

Mr. Robert D. Hackett is a military historian and researcher. Retired from the United States Air Force and later from the aerospace industry, he resides in Florida.

Mr. Sander Kingsepp of Estonia is also a military historian and researcher. He is an editor of a construction magazine. A talented linguist, Sander's translations of Japanese source materials have added immeasurably to these TROMs.

Bob and Sander prepared the TROMs on the IJN's submarines presented on the SENSUIKAN! pages and for the IJN's battleships and cruisers presented on the SENKAN! and JUNYOKAN! pages and are major contributors to the TROMs of various classes of auxiliaries detailed on TOKUSETSU KANSEN! and its related pages.

Questions to the authors concerning these TROMs should be posted on the Discussion and Questions board.