The Kairyu (海龍, Kairyū, "Sea Dragon") was a class of midget submarines of the Imperial Japanese Navy, designed in 1943–1944, and produced from the beginning of 1945.

These submarines were meant to meet the invading American naval forces upon their anticipated approach of Tokyo.

These submarines had a two-man crew and were fitted with two torpedoes along with a 600 kg (1,300 lb) explosive charge intended to be used on a suicide mission.

Most of the Kairyu submarines were based at Yokosuka to defend the entrance of Tokyo Bay in the event of a United States invasion of mainland Japan.

Some of these subs were also stationed in the Moroiso and Aburatsubo inlets on the southern tip of the Miura Peninsula where a training school had also been set up.