(I-8 by Takeshi Yuki scanned from "Color Paintings of
Stories and Battle Histories of the IJN's Midget Submarines
1 June 2018
By Bob Hackett and Sander Kingsepp
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
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.
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
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
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
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
Harbor, Hawaii, 1941 (revised 9/1/17)
Australia, 1942 (revised 3/1/18)
Diego Suarez, Madagascar, 1942 (revised 3/12/08)
1942 (posted 6/23/06)
Solomon Islands, 1942 (revised 4/7/2012)
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
and the Ryukyu Islands, 1944-1945 (posted 1/5/07)
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
Questions to the authors concerning these TROMs should be posted
on the Discussion and Questions board.