SS Mission San Luis Obispo was a Type T2-SE-A2 tanker built for the United States Maritime Commission during World War II.

Mission San Luis Obispo was laid down on 18 April 1944 under a Maritime Commission contract by Marine Ship Corporation, Sausalito, California; launched on 18 June 1944, sponsored by Mrs. George A. Patterson; and delivered on 15 July 1944.

She was transferred to the operational control of the newly created Military Sea Transportation Service (MSTS) on 1 October 1949 as USNS Mission San Luis Obispo (T-AO-127).

Upon completion of the conversion and delivery in January 1967 Seatrain Puerto Rico, IMO 6700468, was chartered to the MSTS in support of overseas U.S. military operations, including the transport of material, equipment, and aircraft to Vietnam.

The ship was transferred to the National Defense Reserve Fleet (James River) on 19 December 1974, and on 27 May 1977, her name was changed to Puerto Rico.