Originally the commercial trawler Annapolis, Merganser was built in 1937 by the Bethlehem Steel Corp., Quincy, Massachusetts; acquired by the U.S. Navy as Ocean through Maritime Commission requisition purchase from the General Sea Foods Corp., Boston, Massachusetts, 3 January 1942; renamed Merganser 18 January 1942; converted by Bethlehem Steel Atlantic Works, East Boston, Massachusetts; and commissioned 23 May 1942, Lt. A. S. Johnson, USNR, in command.