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.
I-121-class submarine
The was a class of submarine in the Imperial Japanese Navy (IJN), serving from the 1920s to the Second World War. The IJN classed it as a . The type name, was shortened to .