The USS Proteus (AC-9) was a cargo ship of the United States Navy, launched on 18 December 1917. It was commissioned on 24 April 1918 and served primarily during World War I, transporting supplies and equipment to support naval operations. After the war, the ship was decommissioned on 30 June 1919 and later transferred to the United States Shipping Board. In 1931, the USS Proteus was reactivated and served in various capacities, including as a transport vessel during World War II. It was finally decommissioned for the last time on 15 November 1945 and was sold for scrapping in 1946, marking the end of its service.