I-20 was one of five Type C cruiser submarines of the C1 sub-class built for the Imperial Japanese Navy. During World War II, she operated as the mother ship for a midget submarine during the attack on Pearl Harbor and the attack of Diego-Suarez, conducted war patrols in the Pacific Ocean and Indian Ocean, and served in the Guadalcanal campaign and New Guinea campaign. She was last heard from on 31 August 1943.