I-18 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 a war patrol in the Indian Ocean, and served in the Guadalcanal campaign before she was sunk in February 1943.

The Cruiser submarine Type-C was one of the first classes of submarine in the Imperial Japanese Navy (IJN) to serve during the Second World War. Type-C submarines were better armed than the Type-A and Type-B. The Type-Cs were also utilized as Kō-hyōteki or Kaiten mother ships, for this reason they were not equipped with aviation facilities.