Clamagore was built by Electric Boat Co. in Groton, Connecticut near the end of World War II. She was launched on 25 February 1945 and commissioned on 28 June 1945, with Commander S.C. Loomis, Jr., taking command. Clamagore was first assigned to Key West, and reported there on 5 September 1945. She operated off Key West with various fleet units and with the Fleet Sonar School, voyaging on occasion to Cuba and the Virgin Islands until 5 December 1947, when she entered Philadelphia Naval Shipyard for GUPPY II modernization and installation of snorkel.