midget submarine
A small submarine, typically for one or two crew, used for special operations or research.
During World War II, the Imperial Japanese Navy deployed midget submarines in the attack on Pearl Harbor.
Obsolete term for a submarine in general; modern Japanese uses 潜水艦 (せんすいかん).
See also: 潜水艦
In old documents, 潜航艇 can refer to submarines in general.