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Kairyu file photo [3414]

Kairyu-class Midget Submarine

BuilderYokosuka Naval Arsenal
Launched1 Jan 1945
Displacement19 tons standard
Length57 feet
Beam4 feet
Machinery85hp gasoline engine, 80hp electric engine
Power Output85 shaft horsepower
Speed7 knots
ArmamentIntended to be equipped with 2x45cm torpedoes, but instead equipped with 600kg of explosives internally
Submerged Speed10 knots


This article refers to the entire Kairyu-class; it is not about an individual vessel.

ww2dbaseThe 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 to 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. Most of them were deployed to Yokosuka near Tokyo, while others were found in the Moroiso and Aburatsubo inlets on the southern tip of the Miura Peninsula. 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.

ww2dbaseSources: Wikipedia; Naval History & Heritage Command; Combined Fleet.

Last Major Revision: Feb 2009


Drawings of both Koryu and Kairyu submarines, copied from Kairyu-class submarines at Yokosuka Naval Base, Japan, Sep 1945, photo 1 of 2
See all 14 photographs of Kairyu-class Midget Submarine

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Visitor Submitted Comments

1. Commenter identity confirmed Bill says:
10 Jan 2013 11:11:15 AM

In 1944 the Japanese Navy developed a much improved version of the midget submarine.
The Type "D" was larger, powered by both a diesel engine, and a 500hp electric motor.

The boat had a crew of five men, was 60 tons and armed with two torpedoes the first HA-77 boats were completed and ready in January 1945 and 500 more were under construction at wars end in August 1945.


Did you know, it took the US about almost five years to completely scrap what was left of the Imperial Japanese Army and Navy, to transport back to Japan and demobilize personnel, military equipment like trucks small generators, motors, tools and other non-type weapons were used in the civilian sector.


Success story: Soichiro Honda of Honda Motor Co. Ltd. who salvaged or bought small motors to power his first motorbikes and motorcycles

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Kairyu-class Midget Submarine Photo Gallery
Drawings of both Koryu and Kairyu submarines, copied from Kairyu-class submarines at Yokosuka Naval Base, Japan, Sep 1945, photo 1 of 2
See all 14 photographs of Kairyu-class Midget Submarine

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