USNS Mission San Diego (T-AO-121)

SS Mission San Diego was a Type T2-SE-A2 tanker built for the United States Maritime Commission during World War II. After the war she was acquired by the United States Navy as USS Mission San Diego (AO-121). Later the tanker transferred to the Military Sea Transportation Service as USNS Mission San Diego (T-AO-121). She was a member of the Mission Buenaventura-class oiler and was named for the Mission San Diego de Alcalá.

Career
Originally laid down as SS Mission San Diego was on 20 December 1943, as a Maritime Commission type (T2-SE-A2) tanker hull under Maritime Commission contract (MC hull 1814) by Marine Ship Corporation, Sausalito, California; launched on 14 March 1944, sponsored by Mrs. E. J. Rising; and delivered on 30 April 1944.

Chartered to Deconhill Shipping Co. upon delivery for operations, she spent the remainder of the war carrying fuel to allied forces overseas in the Pacific (during which time she was awarded the National Defense Service Medal). She was returned to the Maritime Commission on 29 March 1946 and laid up in the Maritime Reserve Fleet at Suisun Bay, California.

Acquired by the Navy on 17 October 1947 she was designated Mission San Diego (AO‑121) and placed under the operational control of the Naval Transportation Service. After 1 October 1949 she was transferred to the newly created Military Sea Transportation Service (MSTS) for duty as USNS Mission San Diego (T‑AO‑121). She served with MSTS until 30 December 1954 when she was returned to MARAD and laid up in the Maritime Reserve Fleet at Olympia, Washington. She was struck from the Naval Vessel Register on 22 June 1955.

Reacquired by the Navy on 3 July 1956 she was placed in service with MSTS, but served only until 16 October 1957 when she was returned to the Maritime Commission and laid up in the Maritime Reserve Fleet at James River, Virginia. She was again struck from the Naval Vessel Register that same date.

Sold to Hudson Waterways Corporation on 10 November 1966 she was renamed SS Seatrain Washington and converted into a combination train ferry and container ship. Into 1969, she still served the United States carrying cargo between the east coast of the United States and the Caribbean, and occasionally Vietnam. Subsequently sold and renamed SS Washington, the ship was ultimately scrapped (date unknown).