Kairyu Midget Submarine

The Kairyu (海龍, "Sea Dragon") was a class of two-man midget submarines developed from a 1943 proposal, with prototypes tested in 1944; emergency mass production was ordered in April 1945. It displaced approximately 19.6 tons and measured about 17.3 meters in length with a hull diameter of approximately 1.4 meters — providing a cramped space for two crewmen.

Propulsion combined an 85 HP diesel engine for surface/battery charging operations and an 80 HP electric motor for submerged running. Maximum surface speed was about 7.5 knots; submerged speed about 10 knots. Range was approximately 450 nautical miles surfaced.

Armament consisted of two 450mm torpedoes as primary weapons, plus a 600 kg explosive charge in the bow for use as a suicide weapon against enemy vessels. The Kairyu was thus designed both as a conventional attack submarine and as a last-resort suicide weapon.

Most Kairyu were based at Yokosuka Naval Base to defend Tokyo Bay against the anticipated American invasion (Operation Downfall). Training was conducted in the Moroiso and Aburatsubo inlets on the Miura Peninsula. By Japan's surrender in August 1945, roughly 200 to 225 had been completed (English-language sources give 200–213, Japanese sources 224) out of a planned 750+ units. None ever saw combat.

Surviving Kairyu are displayed at the US Navy Submarine School in Groton, Connecticut, at the Yamato Museum in Kure, and at the JMSDF First Service School at Etajima.