Japanese Type A Midget Submarine

The Japanese Type A midget submarine on display in Groton CT is one of only four left in the world.

Midget submarine on display

With the near war-winning success of the German U-Boats in the First World War, the navies of the world began serious study of different methods of submarine warfare. One of the concepts that was developed during the 1920s was the “midget submarine”. These were intended to be used primarily for infiltrating enemy harbors and attacking their ships at anchor, but were also tested as methods of shore defense and as a way of striking enemy ships during a surface engagement. There were also plans to use midget subs as stealthy delivery vehicles for commandos and saboteurs.

The British, German and Russian navies all poured serious research into designing and building midget submarines. But by far the most advanced work was done in Japan.

The Japanese program was done entirely in secret. The project was hidden under the name Ko Hyoteki (“improved target ship”) to try to fool any enemy spies into thinking it was just a small unmanned target for naval gunnery practice. In reality, the Type A “target ship” was a remarkably sophisticated offensive weapon, far more capable than anything being developed elsewhere. Only 78 feet long and with a displacement of 46 tons, the tiny craft were fully maneuverable both below and on the surface, and carried enough battery power to run the electric motor for up to 12 hours. They were capable of diving to around 300 feet and on the surface could cruise at 6mph and reach 26mph for short bursts. Most importantly, they were armed with two Type 97 450mm torpedoes, each carrying an 800-pound warhead.

Their one crippling limitation was their short range. Incapable of reaching Chinese ports from Japan on their own, it was intended that they be strapped to the deck of a modified Type C-1 “cruiser” attack submarine and carried as close to their target as possible. The midget subs would then enter the harbor, attack with their torpedoes, and rendezvous back with their mother sub. Because there was no way to re-attach the midget subs to the mother ship, each of them was fitted with a 300-pound explosives charge which was to be detonated after the crew was recovered, or, if necessary during an unsuccessful mission, to prevent the top-secret craft (and its crew) from being captured.

When the planning began in October 1941 for the carrier-based air raid on Pearl Harbor, the Japanese realized that the Type A midget submarine could add a new dimension to the attack. So preparations were made. Five Type A midget subs were modified by adding a net-cutter (for penetrating through anti-submarine nets) and making improvements to the steering system. Five fleet submarines, the I-16, I-18, I-20, I-22 and I-24, were altered to carry a midget sub attached to their deck. 

The five mother submarines departed Japan on November 25, 1941, the day before the six-carrier Imperial Japanese Navy task force. Shortly before midnight on December 6 the subs were within 12 miles of the harbor entrance, and by 3am December 7 they had released all of the midget subs and departed the area.

The plan called for each of the midgets to follow an American warship through the anti-submarine net at the mouth of the harbor and wait inside until the air attack began at 8am, then surface and fire their torpedoes at point-blank range. After the attack, the mini-sub crews were to leave the harbor, scuttle their ships, and wait in the water to be picked up by the waiting Japanese fleet subs I-68 and I-69.

But things went wrong. At 4am the US Navy minesweeper Condor happened to see a strange object that looked like the conning tower of a tiny submarine near the harbor entrance, and called the destroyer Ward over to investigate. After searching for about 90 minutes, the Ward spotted the mini-sub passing through the anti-submarine net in the wake of the cargo ship Antares. The Ward immediately attacked, firing two shots from her deck gun and dropping four depth charges. The first shots at Pearl Harbor had been fired by the Americans.

By 7am, another midget sub, crewed by Ensign Kazuo Sakamaki and Petty Officer Kiyoshi Inagaki, reached the mouth of Pearl Harbor but was not able to get through the anti-submarine net. When the air attack began at 7:55, this midget sub tried again to find a way in but hit a reef and damaged the gyrocompass, forcing her to surface for navigation. She was spotted and shelled by the American destroyer Helm, then depth-charged by a Navy PBY patrol plane, which damaged her further. Now adrift and without power, the crew abandoned the sub. Inagaki drowned, and Sakamaki was captured, making him the first POW of the war to be taken by the Americans.

In May 1942, Japanese midget submarines made another attack, this time at Sydney harbor in Australia. One Australian supply ship was damaged in the attack. Later that same month, an attack by two midget subs in a harbor in Madagascar damaged the British battleship Ramillies, and in subsequent years Japanese midget subs were deployed at Midway, the Aleutians, the Bismarck Islands, the Philippines, the Marianas, and Okinawa.

In all, 46 Type A midget submarines were built during the war, followed by 5 improved Type B and 47 Type C. None of them scored any major successes. Some of the technology used in the midget submarine was later adapted for use in the Kaiten suicide submarine, which was essentially a manned Type 93 torpedo with a 3000-pound warhead and a conning tower added for a pilot. The Kaiten managed to sink two American ships before the end of the war.

Today, one of the four remaining Type A midget subs is on display at the US Submarine Force Museum in Groton CT. It is not entirely certain which particular sub this is. The most likely hypothesis is that it is the Ha-8, which was scuttled by her crew during the Japanese defeat at Guadalcanal in August 1942. The wreck was recovered in the shallow water and was towed to New Caledonia.

Some investigators though have concluded that the mini sub at Groton is in fact the Ha-10, which was launched for a raid on Guadalcanal in November 1942 but lost her steering in an accident and was scuttled and abandoned.

Several other mini subs have also been proposed, with varying degrees of confidence.

The mini sub wreck, whichever one it is, was shipped back to the US, restored, and displayed during War Bond drives in 1945 before going on permanent exhibit at the Submarine Museum.

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