Submarines of the Imperial Japanese Navy
Imperial Japanese Navy submarines originated with the purchase of five Holland type submarines from the United States in 1904. Japanese submarine forces progressively built up strength and expertise, becoming by the beginning of World War II one of the world's most varied and powerful submarine fleets.
Japanese Type 6 submarine
The was the first class of submarines of the Imperial Japanese Navy built domestically in Japan. Consisting of two vessels, these submarines were highly modified versions of "Holland"-class vessels designed in the United States.