Type A Kō-hyōteki-class submarine

Type A Ko-hyoteki-class submarine, No.19, grounded in the surf on Oahu after the attack on Pearl Harbor, December 1941
Class overview
Operators:  Empire of Japan
  • 101
  • 1 × First prototype
  • 2 × Second prototype
  • 46 × Type 'A'
  • 5 × Type 'B'
  • 47 × Type 'C'
General characteristics
Type: Kō-hyōteki kō-gata (甲標的甲型, Target 'A', Type 'A') class midget submarine
Displacement: 46 long tons (47 t) submerged[1]
Length: 23.9 m (78 ft 5 in)[1]
Beam: 1.8 m (5 ft 11 in)[1]
Height: 3 m (9 ft 10 in)
  • 192 trays of two two-volt cells each,
  •  136 trays forward
  •  56 trays aft
  • 1 × electric motor, 600 hp (447 kW)[1] at 1800 rpm
  • 2 × screws counter-rotating on single shaft
  •  leading prop 1.35 m diameter, right-handed;
  •  trailing prop 1.25 m diameter, left-handed
  • 23 knots (43 km/h; 26 mph) surfaced
  • 19 knots (35 km/h; 22 mph) submerged[1]
  • 100 nmi (190 km) at 2 kn (3.7 km/h; 2.3 mph)[1]
  • 80 nmi (150 km) at 6 kn (11 km/h; 6.9 mph)
  • 18 nmi (33 km) at 19 kn (35 km/h; 22 mph)
Test depth: 30 m (98 ft)[1]
Complement: 2[1]
  • 2 × 450 mm (17.7 in) torpedoes, muzzle-loaded into tubes[1]
  • 1 × 300 lb (140 kg) scuttling charge
Notes: Ballast: 2,670 kg (5,890 lb) in 534 × 5 kg lead bars
Not to be confused with Type A submarine.

The Type A Ko-hyoteki (甲標的甲型 Kō-hyōteki kō-gata, Target 'A', Type 'A') class was a class of Japanese midget submarines (Ko-hyoteki) used during World War II. They had hull numbers but no names. For simplicity, they are most often referred to by the hull number of the mother submarine. Thus, the midget carried by I-16-class submarine was known as I-16's boat, or "I-16tou."

This class was followed by: Type B (甲標的乙型 Kō-hyōteki otsu-gata), Type C (甲標的丙型 Kō-hyōteki hei-gata), and Type D (甲標的丁型 Kō-hyōteki tei-gata), the last one better known as Kōryū (蛟龍).[2][3]


Japanese Landing ship No.5 carried Type 'C' No.69.

Fifty were built. The "A Target" name was assigned as a ruse: If their design was prematurely discovered by Japan's foes, the Japanese Navy could insist that the vessels were battle practice targets. They were also called "Tubes" ( Tou) or "Target" ( Teki, abbreviation of 'Hyōteki') and other slang names.

The first two, No.1 and No.2, were used only in testing. They did not have conning towers, which were added to the later boats for stability underwater.

No.19 was launched by I-24 at Pearl Harbor. Most of the other fifty are unaccounted for, although three were captured in Sydney (Australia), and others in Guam, Guadalcanal, and Kiska Island, accounting for some of the other hull numbers.

The submarines were each armed with two 450 mm (17.7 in.) torpedoes in muzzle-loading tubes one above the other at the bow. In the Pearl Harbor attack, the specially designed Type 97 torpedo was used, but problems with the oxygen flasks meant that all later attacks used a different torpedo. Some have stated that a version of the Type 91 torpedo, designed for aircraft launching, was used, but other reports[4] indicate that the Type 97 torpedo was modified to the Type 98, otherwise known as the Type 97 special. There is no definitive information that the Type 91 was used. The Type 98 was later supplanted by the Type 02 torpedo. There was also a demolition charge which it has been suggested was large enough to enable the submarine to be used as a suicide weapon, but there is no evidence that it was ever used as one.

Each submarine had a crew of two men. A junior officer conned the boat while a petty officer manipulated valves and moved ballast to control trim and diving.[1]

Pearl Harbor attack

Raising of midget submarine No.18 from Keehi Lagoon by USS Current (ARS-22) in 1960
Japanese Type A Midget Submarine recovered in 1960 off Pearl Harbor, HI.

Five of these boats participated in the Pearl Harbor attack, with two actually making it into the harbor. Of the five used at Pearl Harbor, No.19 was captured with its pilot Kazuo Sakamaki where it grounded on the east side of Oahu. During World War II, No.19 was put on tour across the United States to help sell War Bonds.[5] Now a U.S. National Historic Landmark, No.19 is an exhibit at the National Museum of the Pacific War in Fredericksburg, Texas.[5]

A second Pearl Harbor midget submarine, No.18, was located by U.S. Navy divers off Keehi Lagoon east of the Pearl Harbor entrance on 13 June 1960.[1] The submarine had been damaged by a depth charge attack and abandoned by its crew before it could fire its torpedoes.[1] This submarine was restored and placed on display at the Imperial Japanese Naval Academy at Etajima on 15 March 1962.[1]

The midget submarine attacked by Ward (DD-139) at 6:37 a.m. on 7 December, No.20, was located in 400 meters (1,312 feet) of water five miles outside Pearl Harbor by a University of Hawaii research submersible on 28 August 2002.[6]

A fourth submarine, No.22, entered the harbor and fired its torpedoes at Curtiss (AV-4) and Monaghan (DD-354). Both of those torpedoes missed and are believed to have hit a dock at Pearl City and the shore of Ford Island.[1] This submarine was sunk by Monaghan at 8:43 a.m. on 7 December and later recovered and used as fill during construction of a new landside pier at the Pearl Harbor submarine base. The hulk was uncovered again in 1952 but was so badly corroded by chlorine gas from the electrical batteries that it was again reburied at the same location. The crew's remains are still entombed in the submarine.[1][7]

In 2009, a research team assembled by PBS Nova positively identified the remains of a midget sub found outside the Pearl Harbor entrance as being the last, No.16, of the 5 Ko-Hyoteki that participated in the December 7, 1941, attack. It was discovered in salvage from the wreckage of the West Loch Disaster of 1944, dumped three miles south of Pearl Harbor. Secret war records show that submarine crews had been ordered to scuttle their subs after the attack and provisions were made to recover stranded crews. It is believed the fifth sub successfully entered Pearl, fired on Battleship Row, and escaped to the relative quiet of neighboring West Loch, where it was scuttled by the crew. When a series of explosions sank an amphibious fleet being assembled in the Loch in 1944, the remains of the sub were collected and dumped in the subsequent salvage operation, which was kept classified as secret until 1960. The torpedo tubes in the bow section were empty, indicating that the fifth midget had fired its torpedoes prior to being scuttled. A photograph[8] taken from a Japanese plane during the Pearl Harbor attack appears to show a midget submarine inside the harbor firing torpedoes at Battleship Row. This new evidence suggests that the capsizing of the USS Oklahoma may have been accelerated by a torpedo hit from a submarine-launched torpedo, the warhead of which was roughly twice the power of that carried by the air-dropped torpedoes. In the photo, where the torpedoes' paths had supposedly started, were sprays that indicated a midget-submarine rocking up and down due to the force of the torpedo being launched, causing the propellers of the stern to be exposed, kicking up clouds of water spray. A war time report from Admiral Nimitz confirmed the recovery of dud torpedoes of the type employed by the midget submarines.[9] This discovery is covered in PBS Nova television program Killer Subs in Pearl Harbor[10] and companion website, I-16tou.com.[11]

Japanese midget submarine attacks on Sydney

HMAS Kuttabul after sinking.
The two midget submarines sunk in Sydney Harbour were used to construct a composite midget submarine which toured Australia during the war.

On the night of 29 May 1942, five large Japanese submarines positioned themselves 56 kilometres north-east of Sydney Heads. At 3 a.m. the next day one of the submarines launched a reconnaissance aircraft. After circling Sydney Harbour the aircraft returned to its submarine, reporting the presence of 'battleships and cruisers' moored in the harbour. The flotilla's commanding officer decided to attack the harbour with midget submarines the next night. The next day the five submarines approached to within 11 kilometres of Sydney Heads, and at about 4:30 p.m. they released three midget submarines, which then began their approach to Sydney Harbour.

The outer-harbour defences detected the entry of the first midget submarine, No.14, at about 8 p.m., but it was not identified until it became entangled in an anti-torpedo net that was suspended between George's Head and Green Point. Before HMAS Yarroma was able to open fire, the submarine's two crew members destroyed their vessel with demolition charges and killed themselves.

The second submarine, No.24b, entered the harbour at about 9.48 p.m. and headed west towards the Sydney Harbour Bridge, causing a general alarm to be issued by the Naval Officer in Charge, Sydney. About 200 metres from Garden Island the submarine was fired on by the heavy cruiser USS Chicago. The submarine then fired its two torpedoes at the cruiser. One torpedo ran ashore on Garden Island, but failed to explode. The other passed under the Dutch submarine K9 and struck the harbour bed beneath the depot ship HMAS Kuttabul where it exploded, killing 21 sailors (19 Royal Australian Navy and 2 Royal Navy). The submarine then slipped out of the harbour, its mission complete, and disappeared. Its wreck was located, about 30 km north of the harbour and 5 km to seaward, in November 2006. It is now protected as a war grave.

The third submarine, No.21, was sighted by HMAS Yandra at the entrance to the harbour and was depth-charged. Some four hours later, having recovered, it entered the harbour, but it was subsequently attacked with depth charges and sunk in Taylor Bay by vessels of the Royal Australian Navy. Both members of the submarine's crew committed suicide.

The two submarines that were recovered were identical, and their remains were used to reconstruct a complete submarine, which toured New South Wales, Victoria and South Australia before being delivered to the Australian War Memorial in Canberra in 1943, where it remains on display.

Japanese midget submarine attacks on Madagascar

Main article: Battle of Madagascar

On the 29 May 1942, the Japanese submarines I-10, I-16 and I-20 arrived at Madagascar. I-10's reconnaissance plane spotted Revenge-class battleship HMS Ramillies at anchor in Diego Suarez harbor but the plane was spotted and Ramillies changed her berth. I-20 and I-16 launched two midget submarines, one of which managed to enter the harbor and fired two torpedoes while under depth charge attack from two corvettes. One torpedo seriously damaged Ramillies, while the second sank the 6,993 ton oil tanker British Loyalty (later refloated). Ramillies was later repaired in Durban and Plymouth.

The crew of one of the submarines, Lieutenant Saburo Akieda and Petty Officer Masami Takemoto, beached their submarine (No.20b) at Nosy Antalikely and moved inland towards their pick-up point near Cape Amber. They were informed upon when they bought food at a village and both were killed in a firefight with Royal Marines three days later. The second midget submarine, No.16b, was lost at sea and the body of one of its crew was found washed ashore a day later.


according to Rekishi Gunzō[12]
Type First prototype Second prototype
(Prod. No. 12)
Type A
(Prod. No. 352)
Type B
(Prod. No. 4953)
Type C
(Prod. No. 54100)
41.525 long tons (42 t) 44.150 long tons (45 t) 46 long tons (47 t) 47 long tons (48 t) 49.09 long tons (50 t)
Length (overall) 23.3 m (76 ft 5 in) 23.9 m (78 ft 5 in) 23.9 m (78 ft 5 in) 24.9 m (81 ft 8 in) 24.9 m (81 ft 8 in)
Beam 1.824 m (5 ft 11.8 in) 1.85 m (6 ft 1 in) 1.85 m (6 ft 1 in) 1.85 m (6 ft 1 in) 1.88 m (6 ft 2 in)
Draft 3.074 m (10 ft 1.0 in) 3.1 m (10 ft 2 in) 3.4 m (11 ft 2 in) 3.4 m (11 ft 2 in) 3.43 m (11 ft 3 in)
Draught 1.854 m (6 ft 1.0 in) 1.88 m (6 ft 2 in) 1.88 m (6 ft 2 in) 1.85 m (6 ft 1 in) 1.88 m (6 ft 2 in)
Propulsion 224 × Type 'B' special rechargeable batteries,
electric motor (600 bhp),
single shaft,
contra-rotating propellers
224 × Type 'D' special rechargeable batteries,
electric motor (600 bhp),
single shaft,
contra-rotating propellers
224 × Type 'D' special rechargeable batteries,
electric motor (600 bhp),
single shaft,
contra-rotating propellers
224 × Type 'D' special rechargeable batteries,
electric motor (600 bhp),
1 × electric generator (40 bhp),
single shaft,
contra-rotating propellers
208 × Type 'D' special rechargeable batteries,
electric motor (600 bhp),
1 × electric generator (40 bhp),
single shaft,
contra-rotating propellers
Speed Surfaced no data no data no data 6 knots (11 km/h) 6 knots (11 km/h)
Submerged 25 knots (46 km/h) 25 knots (46 km/h) 19.0 knots (35.2 km/h) 19.0 knots (35.2 km/h) 18.5 knots (34.3 km/h)
Range Surfaced no data no data no data 500 nmi (930 km) at 6 knots (11 km/h) 500 nmi (930 km) at 6 knots (11 km/h)
Submerged no data no data 15.8 nmi (29.3 km) at 9 knots (17 km/h)
84 nmi (156 km) at 6 knots (11 km/h)
15.8 nmi (29.3 km) at 9 knots (17 km/h)
84 nmi (156 km) at 6 knots (11 km/h)
15.4 nmi (28.5 km) at 8.5 knots (15.7 km/h)
120 nmi (220 km) at 4 knots (7.4 km/h)
Test depth 100 m (330 ft) 100 m (330 ft) 100 m (330 ft) 100 m (330 ft) 100 m (330 ft)
crew 2 2 2 2 3
Armament 2 × 533 mm (21 in) Type 89 torpedoes 2 × 450 mm (18 in) Type 97 torpedoes 2 × 450 mm (18 in) Type 97 torpedoes, later replaced Type 2 Torpedo 2 × 450 mm (18 in) Type 2 torpedoes 2 × 450 mm (18 in) Type 2 torpedoes
Builder Kure Naval Arsenal Kure Naval Arsenal Karasukojima Naval Armony (Production number 320)
'P' (Ōurasaki) Naval Armony (Production number 2152)
'P' Naval Armony 'P' Naval Armony
Number built 1 2 50
Production number 4952 were rebuilt to the Type 'B' in 1943, some boats rebuilt to the Type 'A' trainer.
Production number 4952 were rebuilt from the Type 'A'.
Approx. 10 boats were rebuilt to the Type 'C' trainer.
Building period[13] 19321933 19381940 19401943 1943 19431944
Ko-hyoteki Characteristics
No.8 on display at the Submarine Force Library and Museum 
The stern of No.8 showing contra-rotating propellers 

See also

Media related to Ko-hyoteki class submarine at Wikimedia Commons


  1. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Stewart, A.J., LCDR USN. "Those Mysterious Midgets", United States Naval Institute Proceedings, December 1974, p.55-63
  2. Kemp, Paul; Hill, David (1999). Midget submarines of the Second World War. Chatham. pp. 58–59, 76. ISBN 1-86176-042-6.
  3. Jameson, John H.; Scott-Ireton, Della A. (2007). Out of the Blue: Public Interpretation of Maritime Cultural Resources. Springer. p. 184. ISBN 0-387-47861-2.
  4. US Naval Technical Mission to Japan : Report on Japanese Kaiten and Torpedoes, 1946
  5. 1 2 "Japanese HA-19", Historical Naval Ships Association
  6. "The Search for the World War II Japanese Midget Submarine Sunk off Pearl Harbor, December 7, 1941". Retrieved 2008-09-07.
  7. Lord, 1957, picture section 2 pg. 15
  8. http://ww2db.com/images/battle_pearl3.jpg
  9. Maugh, Thomas H., II, "Pearl Harbor mini-submarine mystery solved? Researchers think they have found the remains of a Japanese mini-submarine that probably fired on U.S. battleships on Dec. 7, 1941", Los Angeles Times, December 7, 2009
  10. "Killer Subs in Pearl". PBS. 01.05.10. Retrieved 2012-05-27. Check date values in: |date= (help)
  11. "I-16tou.com". Retrieved 2009-01-05.
  12. Rekishi Gunzō, pp. 39-46.
  13. Rekishi Gunzō, pp. 80-95.

External links

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