1944-1949

1950-1959

1960-1989

San Marcos ' keel was laid down on 1 September 1944 at the Philadelphia Navy Yard. She was launched on 10 January 1945, and commissioned on 15 April 1945 with Commander L. E. Ellis in command.

San Marcos completed shakedown in early May, took on a cargo of landing boats; and, on 19 May, sailed for the Panama Canal and Pearl Harbor. Arriving on 24 June, she transferred her cargo of 40 boats, loaded a similar cargo, and departed on 29 May. After taking on dredging equipment at Guam, she anchored in Buckner Bay, Okinawa, on 12 August – three days before the cessation of hostilities. On 15 August, she shifted to Naha, repaired tank landing craft (LCTs) through 20 August, then, proceeded to Saipan. There, she loaded mechanized landing craft (LCM-6s), vehicle and personnel landing craft, (LCVPs, "Higgins boats"), and large personnel landing craft (LCPLs), for use by occupation forces in the Tokyo Bay area; and, on 4 September, she arrived in Japan to offload her cargo and to commence operation and maintenance of a boat pool. In early December, she was reassigned to cargo operations; and, through the end of the year, she ferried boats from Aomori toYokohama.

In January 1946, San Marcos was assigned to Joint Task Force 1 (JTF 1) forOperation Crossroads, the series of atomic tests scheduled for Bikini Atoll during the summer. She first shifted south to Okinawa; then, in February, moved east toKwajalein, whence she helped to prepare the test site. She remained in JTF 1 through the July tests, and, on 29 August, she was detached. In early September, the ship moved from the Marshall Islands to Hawaii; and, in October, she arrived at San Francisco.

Granted provisional radiological clearance, she resumed cargo operations along the west coast in early November; and, by the end of the month, was carrying supplies, boats, and vehicles to the Aleutian Islands. In December, she put into the Puget Sound Navy Yard at Bremerton; received final clearance in January 1947; and, in the spring, resumed cargo runs between the west coast and the Aleutians. She terminated those operations in September and proceeded to southern California where her capabilities as a temporarily converted seaplane drydock were tested. In December, she commenced inactivation, and, on 19 December, was decommissioned and berthed with the San Diego Group of the Pacific Reserve Fleet.