I-123, originally named Submarine No. 50 then renamed I-23 from before her construction began until June 1938, was an of the Imperial Japanese Navy that served during the Second Sino-Japanese War and World War II. During the latter conflict, she conducted operations in support of the Japanese invasion of the Philippines, the Battle of Midway, the Guadalcanal campaign, and the Battle of the Eastern Solomons. She was sunk in 1942.