World War II Database

By definition, a midget submarine is less than 150 tons, has a crew of no more than eight, has no on-board living accommodation, and operates in conjunction with a mother ship to provide the living accommodations and other support. The Japanese Navy built at least 800 midgets in 7 classes, but only a fraction had any noticeable impact on the war. Their intended purpose initially was to be deployed in front of enemy fleets, but their actual use would be in harbor attacks and coastal defense.

The Japanese kept no comprehensive shipbuilding records for their midget submarines. What is known about these crafts was pieced together from a variety of sources, and some authors still do not agree over some details.

Midget subs were not named but were numbered with "Ha" numbers (e.g., Ha-19). These numbers were not displayed on the exterior and operationally the midgets were referred to according to the numbers of their mother ships. Thus, when I-24 launched Ha-19, the midget was known as "I-24tou" (designated "M24" in some texts). The "Ha" numbers were not unique either; some Type D's were numbered Ha-101 through Ha-109 and SS-Type medium submarines used the same numbers.

Midget Submarine Types

Ko-hyoteki Ko Gata Type A

Ko-hyoteki Ko Gata Type A midget submarines were 78.5 feet long, displaced 46 tons, were armed with two muzzle-loaded torpedoes, and had a crew of two. Normally, they were transported to and from their target areas on the decks of larger Type C1 submarines. About 60 Type A's were built and were the first midgets to be deployed.

Ko-hyoteki Otsu Gata Type B

Just one Ko-hyoteki Otsu Gata Type B Midget prototype was built in 1942 to test improvements to the Type A. Some sources suggest that a few Type A's were retrofitted into Type B's, but sources conflict.

Ko-hyoteki Hei Gata Type C

15 Ko-hyoteki Hei Gata Type C Midgets were made and none were used operationally, according to most sources. These were also improved versions of the Type A with a crew of 3, diesel generator, and an increased radius. Some sources say as many as 47 boats were built with 15 being deployed. Given that one Type C wreck was recovered from the waters around Guam, some manner of deployment seems apparent.

Koryu Tei Gata Type D

In mid-1944, with coastal defense requirements becoming urgent, the Japanese Navy developed the Koryu Tei Gata Type D. More than just another improved version of the Type A, this was a new design. They were the largest of Japan's midgets, displacing about 60 tons, 86 feet in length, with a five-man crew, featuring a more powerful diesel engine, and had improved operating endurance. Koryu's had the same armament as the Ko-hyoteki's: two muzzle-loaded 17.7-inch torpedoes. As with the earlier types, individual boats had alpha-numeric names in the "Ha" series beginning with Ha-101. 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.

Kairyu

The small Kairyu type midget submarines displaced somewhat over 19 tons. Their length varied, with the largest being about 57 feet long. Hull diameter was 4.5 feet, creating a tight fit for the two-man crew. They were intended to defend the entrance Tokyo Bay and for local defense against the prospective invasion that confronted Japan in 1945. The design, which featured diving planes mounted on the hull amidships, was tested in 1943-44 with production beginning in early 1945. Over 760 of these submarines were planned, but about 200 were delivered by war's end in August 1945. Though originally designed to carry two 17.7-inch torpedoes externally, a torpedo shortage caused most, if not all, to be fitted with a 1300-pound internal warhead for employment on suicide missions. Some units used for training had a second periscope mounted at the rear of their streamlined conning tower. Due to Japan's surrender in August 1945, none of these submarines ever saw action.

Kaiten

The Kaiten were truly human guided torpedoes. Many authors do not include the Kaiten as a midget submarine since it is more of a person going on a torpedo ride; but they were machines whose design included transporting a person under the water and they fit the midget sub definition otherwise, the Kaiten is included here.

Kaitens were the first Japanese "Special Attack" weapons, vehicles whose use involved the certain death of the crew, though their first successful use followed the Kamikaze 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 24-inch Type 93 torpedo. A new 39-inch forward section containing the warhead, additional fuel, 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 and a range of 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 warhead, was capable of producing catastrophic damage in the target ship. Over 300 Type 1 Kaitens were produced in 1944-45; but only two are known to have been used to successfully sink enemy vessels.

Larger Kaiten Type 2 and Type 4 had hulls about 4.5 feet in diameter and 55 feet long. The warhead was as large or larger than that of the Type 1 and performance was better. The Type 2 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 of similar size to the Types 2 & 4 and a Type 10. Only the Type 1 was deployed operationally, however.

Operational Uses

Pearl Harbor - 7-Dec-1941

Five Ko-hyoteki Type A's armed with type 97 torpedoes were launched from five Type C1 mother-submarines as part of the attack on Pearl Harbor. Their orders were to attack any ships that attempted to leave the harbor.

One of these five midget submarines, I-18tou (the midget launched from mother-submarine I-18) was depth-charged in Keehi Lagoon outside Pearl Harbor between the harbor entrance and Honolulu, now under the extended runways of Honolulu International Airport (US Navy divers recovered her wreck on 13-June-1960 with both torpedoes still aboard).

I-24tou (Ha-19) lost her way due to a malfunctioning gyrocompass, ran up on reefs twice, and finally grounded herself on Waimanalo Beach on Oahu's east shore. The sub was captured with both torpedoes still in her tubes and her commanding officer became the first Japanese POW of the war.

I-20tou was spotted as it was entering the harbor and was sunk by gunfire from USS Ward (NOAA's Hawaii Undersea Research Laboratory [HURL] located her wreck offshore in August 2002 with both torpedoes still aboard).

I-22tou entered Pearl Harbor and fired both torpedoes toward USS Curtiss and USS Monaghan just after the air attack started. One torpedo ran aground on Ford Island and the other hit a pier off Pearl City. Monaghan rammed and then depth-charged the sub. (The wreck was recovered shortly after the attack and later in the war was used as fill during an expansion of the Pearl Harbor Submarine Base. The hulk was dug up in the 1960's but reburied almost immediately. According to some sources, the remains of her crew remain aboard.)

I-16tou sent a radio report during the evening of December 7th that the attacks had been successful and claimed credit for sinking USS Arizona. Photographic analysis conducted by independent researchers published by the United States Naval Institute in 1999 suggests a Type A inside the harbor successfully fired torpedoes at USS West Virginia and USS Oklahoma during the air attack. I-16tou was never picked up by any of the mother-subs and the submarine's final resting place is not known.

Light Cruiser USS St. Louis reported she was fired upon by a midget submarine as she broke out of Pearl Harbor at about 0930-1000 but the "two torpedoes" exploded against a submerged reef before reaching the ship. Destroyers pounded the area of the sub with depth charges as St. Louis continued on her sortie.

It would seem there were not enough torpedoes for all these attacks to have come from the five midgets. Six of the ten torpedoes deployed were still in the tubes of their sunken or captured vessels and two were fired at Curtiss and Monaghan inside the harbor. The photo analysts suggest two torpedoes were fired against Battleship Row and St. Louis reported two torpedoes were fired at her. That's 12 torpedoes. All of the 22 large Japanese submarines deployed around Oahu at the time survived the trip to Hawaii and none reported firing any torpedoes that day. The photo analysis was first printed in 1999, three years before the wreck of I-20tou was discovered with both torpedoes still aboard. So at the time these conclusions were published, two torpedoes were unaccounted for. With the discovery of I-20tou in 2002, the question is reduced to which account is more credible: the attack on Battleship Row or the attack on St. Louis. The authors of the 1999 photo analysis have authoritatively repeated their conclusions in several forums recently, but under objective scrutiny they do not hold up.

Sydney Harbor - 31-May-1942

At 0300 on 30 May 1942 one of five large Japanese submarines launched a reconnaissance aircraft northeast of Sydney, Australia. After circling the harbor, the plane returned reporting "battleships and cruisers" in the harbor. In reality, the largest ship present was the heavy cruiser USS Chicago. The flotilla's commander decided to attack the harbor with midget submarines the next night. The next day the five submarines approached Sydney Heads and released three Type A midget submarines at about 0430 to begin their approach to Sydney Harbor.

The outer-harbor defenses detected the entry of the first midget submarine at about 2000 hours, 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 entered the harbor at about 2148 and headed west towards the Harbor Bridge, causing a general alarm to be issued by the Naval Officer in Charge, Sydney. About 200 yards from Garden Island the submarine was fired on by the cruiser 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 harbor bed beneath the depot ship HMAS Kuttabul where it exploded, killing 21 sailors: 19 Royal Australian Navy and 2 Royal Navy. Its mission complete, the submarine then slipped out of the harbor and disappeared (her wreck was located in November 2006 about 20 miles north of the harbor; it is now protected as a war grave).

The third submarine was sighted by HMAS Yandra at the entrance to the harbor and was depth-charged. Some four hours later, having recovered, it entered the harbor 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 from inside the harbor were identical. Their remains were used to reconstruct one complete submarine that toured Australia for a year before being delivered to the Australian War Memorial in Canberra in 1943, where it still remains on display.

Diego Suarez, Madagascar - 30-May-1942

Japanese submarines I-10, I-16 and I-20 arrived off Madagascar 29 May 1942. I-10's scout plane spotted the 31,000 ton battleship HMS Ramillies at anchor in Diego Suarez harbor but the aircraft was spotted and Ramillies changed her berth. On 30-May-1942 I-20 and I-16 launched two Type A midget submarines, one of which managed to enter the harbor and fire two torpedoes while under depth charge attack from two corvettes. One torpedo seriously damaged Ramillies, while the second sank an oil tanker British Loyalty (later refloated). Ramillies was later repaired in Durban, South Africa and Plymouth, England before sailing with distinction in the Normandy Invasion.

One of the submarines was beached at Nosy Antalikely and the crew moved inland towards their pick-up point near Cape Amber. When they bought food at a village, they were informed upon and they were both were killed by Royal Marines a few days later. The second midget submarine was lost at sea and the body of one its crew washed ashore a day later.

Other Operations

Type A and Type D boats also were employed off Guadalcanal and the Solomon Islands in 1942-43, where they achieved modest success against U.S. shipping. They were deployed around Midway, the Aleutians, the Bismarck Islands, the Philippines, the Marianas, and Okinawa as shore-based defensive units, but their overall effectiveness was negligible at best.

On 20 November 1944, five submarine-launched Kaitens penetrated the US anchorage at Ulithi in the Caroline Islands. Only one had any success, however, sinking the fleet oiler USS Mississinewa amidst pillars of thick black smoke that could be seen throughout the fleet. Eight months later on 24 July 1945, east of the Philippines, another Kaiten sunk the Buckley-class destroyer escort USS Underhill. These two incidents are the only confirmed successful Kaiten attacks, although some Japanese sources list higher numbers.

For more information:

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Visitor Submitted Comments

1. The MAN says:
   1 Nov 2009 06:55:12 PM
   
   i think they should put a few written letters, or any other written source on this. it will help many people about the feelings people were going through at the time

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