I-18 was a Type C submarine of the Imperial Japanese Navy. On 7 December 1941 she was off Oahu for the attack on Pearl Harbor. From that offshore position she launched a midget submarine.
The boat herself stayed outside the harbor. Her part that day was the launch off Pearl Harbor, and she remained clear of the entrance.
On 11 February 1943, south of San Cristobal, a floatplane from Helena found her. Fletcher depth-charged the submarine after that sighting. The depth-charge attack sank I-18. She was lost with all hands.