Mercer, a barracks ship built on an LST hull, commenced her career of berthing and messing large numbers of naval personnel at New York on 7 November 1945. Transferred to the Inactive Fleet in January 1946, she remained at New York until 9 September, when she got underway for Orange, Texas, and remained in duty there until the spring of 1947. She then headed for Green Cove Springs, Florida, where she was decommissioned on 18 June 1947, but remained in service with the Florida Group, Atlantic Reserve Fleet.