LST-857 was laid down on 19 September 1944 at Seneca, III., by the Chicago Bridge & Iron Co.; launched on 6 December 1944; sponsored by Mrs. Beatrice S. Major; and commissioned on 29 December 1944, Lt. Roy C. Parlier in command.
During World War II, LST-857 was assigned to the Asiatic-Pacific theater and participated in the assault and occupation of Okinawa Gunto in June 1940. Following the war, she performed occupation duty in the Far East until mid-December 1945. After postwar operations with the Pacific Fleet, LST-857 performed extensive service during the Korean War. On 1 July 1955, the ship was redesignated King County (LST-857) (q.v.) after counties in Texas and Washington. In October 1957, she began conversion to an experimental guided missile test ship and was reclassified AG-157 on 17 May 1958. Decommissioned on 8 July 1960, King County was sold to Zidell Explorations, Inc., Portland, Oreg., on 25 April 1961.
LST-857 received one battle star for World War II service and seven battle stars for Korean service.