Japanese Type D Koryu midget submarines in drydock, 1945
By definition, a midget submarine is less than 150 tons, has a crew of no more than eight, has no onboard accommodations, and mates with a mother ship to provide accommodations and other support. Works.
The Japanese Navy built at least 800 midgets in 7 classes, but only a fraction had any noticeable effect on the war. Their intended purpose was initially to be deployed in front of enemy fleets, but their actual use would be in port attacks and coastal defence.
Japanese dwarf subs were not named, but were numbered with a "ha" number (eg, Ha-19). These numbers were not displayed on the exterior and operationally referred to the dwarves according to their parent ship numbers.
Thus, when I-24 launched the Ha-19, the midget was known as "I-24tou" (designated "M24" in some texts). The "ha" numbers were also not unique; Some Type D numbers were carried from the Ha-101 to the Ha-109.
In mid-1944, with the urgent need for coastal defense, the Japanese Navy developed the Koryu te Gata Type D. More than just a more advanced version of the Type A, it was a new design.
They were Japan's largest midgets, measuring about 60 tons, 86 feet (26 m) in length, with a five-man crew, featuring a more powerful diesel engine, and improved operational endurance.
Koryu's armament consisted of two muzzle-filled 17.7-inch torpedoes. Like the earlier variants, the "Ha" series, starting with the HA-101, had alpha-numeric names for the individual boats.
When Japan surrendered in August 1945, about 115 units had been completed. At the end of the war, Allied occupation forces received hundreds of midget submarines built in Japan, including a large number of "Koryu"-type submarines; About 500 more were under construction. Some of these submarines were intended for training pilots for the Caten-type manned torpedoes, which had an enlarged conning tower and two periscopes.
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