Ro-33 was an Imperial Japanese Navy "Ro-33"-class submarine. Completed and commissioned in October 1935, she served during World War II in the South China Sea, Indian Ocean, and southwestern Pacific Ocean and operated in support of Japanese forces in the invasion of British Malaya, the invasion of Java, the Battle of the Coral Sea, the Guadalcanal campaign, and the New Guinea campaign. She was sunk in August 1942 during her fifth war patrol.