Japanese submarine I-73 was a Kaidai class submarine that participated in the attack on Pearl Harbor as part of the 3rd Submarine Squadron in the 6th Fleet of the Imperial Japanese Navy. It was one of the vessels created as part of Japan's 1st Naval Armaments Supplement Programme in 1931. On 9 January 1942, I-73 became the first warship to be sunk by a United States Navy submarine; USS Gudgeon fired three torpedoes at I-73 and destroyed it. Gudgeon claimed that the torpedoes only damaged I-73, but Station HYPO confirmed the loss.