Japanese Midget Submarines

photo by John Hughes
Type D ("Koryu" or "Sea Dragon") Midget Submarine
(Photo taken in 1957, just inside the main gate at Fleet Activities-Yokoska)

In mid-1944, with coastal defense requirements becoming urgent, the Japanese Navy developed an improved version of the Type A, B & C midget submarines. Designated "Type D" and nicknamed "Koryu", the new design was somewhat larger than the earlier types, featured a more powerful diesel engine and had improved operating endurance. The "Koryu" also had a five-man crew, two more than in the Type C, but the same armament of two 45cm (17.7") diameter torpedoes.

photo by John Hughes
Type D Midget Submarine (cut away to show details)

The Type D midgets displaced about 60 tons and were 86 feet long. Propelled by a 500 horsepower electric motor, maximum submerged speed was 16 knots. On the surface, with an 150 HP diesel charging the electric batteries, speed was 8 knots and range about 1000 nautical miles. As with the earlier types, individual boats had alpha-numeric names in the "HA" series.

The the first Type D boat, HA-77, was completed in January 1945. Some 115 units had been completed when Japan capitulated in August 1945. Nearly 500 more were under construction. Some of these submarines, intended for training pilots for "Kaiten" type manned torpedoes, had an enlarged conning tower and two periscopes.




From 1934 to 1944, the Japanese Navy built several dozen midget submarines for combat use. They were originally intended to be carried by larger Japanese ships and deployed in the path of an enemy fleet, where they would disrupt its operations with torpedo attacks. However, during the Second World War, the midgets were used for special operations against ships in enemy harbors, among them the 7 December 1941 Pearl Harbor attack and May 1942 raids on Sydney, Australia, and Diego Suarez in the Indian Ocean. The boats also were employed off Guadalcanal in 1942-43, where they achieved modest success against U.S. shipping, and as shore-based defensive units in the Aleutians and elsewhere in the Pacific war zone.

Type A midgets displaced 46 tons, were 78 feet long and carried two 45cm (17.7") diameter torpedoes. Powered by electric motors, they were capable of very high speeds (about 20 knots), but had very limited range. To increase endurance, the prototype Type B and production Type C boats were fitted with a diesel engine to recharge their electric batteries. They had an additional crew member, were slightly longer and heavier, but otherwise resembled the Type A.

Approximately sixty production Type A midget submarines were built between 1934 and 1942, and given alpha-numeric names in the "Ha" series (Ha-1 through Ha-52 and Ha-54 through possibly Ha-61). The single Type B (Ha-53) and fifteen Type Cs (Ha-62 through Ha-76) were built in 1943-44.


photo by John Hughes
Kaiten Type 2 Human Torpedo (note damage to sail from 3" US naval shell)

"Kaiten" type human torpedoes were the first Japanese "Special Attack" weapons, vehicles whose operational use involved the certain death of the crew, though their first successful employment followed that of the "Kamikaze" suicide aircraft by about a month. Proposals for human torpedoes were made in 1943 and were approved in early 1944, initially with provision for the survival of the operator. However, the extreme peril facing Japan after the loss of the Marianas in June 1944 led to acceptance of the pilot's death as an inevitable consequence of "Kaiten" use.

The initial "Kaiten", Type 1, was converted from a Type 93 61-centimeter (24-inch) diameter torpedo. A new 1-meter diameter forward section, containing the warhead, additional fuel and oxygen tanks and the pilot's compartment was grafted to the torpedo's middle and after sections, producing an overall length of just over 48 feet. Speed could be varied from 12 knots, giving a range of some 85,000 yards, to 30 knots. Range at the higher speed was about 25,000 yards. For guidance, the pilot had a short periscope. The "Kaiten's " immense 3400-pound explosive warhead, more than three times the size of the Type 93 torpedo's original (and very effective) warhead, was capable of producing catastrophic damage in the target ship. Over 300 Type 1 "Kaitens" were produced in 1944-45.

The larger "Kaiten" Type 2 and Type 4 human torpedoes had hulls about 4 1/2 feet in diameter and 55 feet long. Warhead was as large or larger than that of the "Kaiten" Type 1 and performance was better. The Type 2, featuring hydrogen-peroxide as oxidizer, was not built in any quantity but some 50 of the less-ambitious Type 4's were reportedly built in 1945. There was also an experimental Type 3 "Kaiten" of similar size to the Types 2 & 4, and a Type 10. The latter was converted from 53 centimeter (21-inch) diameter Type 92 electrically-powered submarine torpedoes.

A large number of Japanese submarines and some surface ships were fitted as "Kaiten" carriers, but there were only a few operational successes. On 20 November 1944, a submarine-launched "Kaiten" penetrated the U.S. anchorage at Ulithi, in the Caroline Islands, and sank the oiler USS Mississinewa (AO-59). Eight months later, eastward of the Philippines, another human torpedo caused the loss of destroyer escort USS Underhill (DE-682).






Derick S. Hartshorn - 2009-present
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