The ship, a Type T2-SE-A3 tanker, was completed as SS Mission Santa Ana and delivered after the end of World War II.

The tanker was acquired by the U.S. Navy in 1948 as USS Mission Santa Ana (AO-137), but was transferred to the Military Sea Transport Service upon its creation in 1949.

Originally laid down as Concho on 18 April 1945 as a Maritime Commission type (T2-SE-A3) tanker hull under Maritime Commission contract (MC hull 1828) by Marinship Corporation of Sausalito, California; launched on 25 July 1945, sponsored by Mrs. D. J. Johnson; and delivered on 25 October 1945.

Chartered to Pacific Tankers Inc. for operations, she carried fuel to American forces stationed overseas (during which time she was awarded the National Defense Service Medal) until 3 April 1946 when she was returned to the Maritime Commission and laid up in the Maritime Reserve Fleet at Columbia River, Oregon.

She served with MSTS until 3 April 1950 when she was taken out of service and berthed in the San Diego group of the Pacific Reserve Fleet.