The first Navy ship to be named Mockingbird, AMc-28, a wooden dragger built in 1936 as Rio Douro by Morse Shipyards, Thomaston, Maine, was purchased by the U.S. Navy from L. C. McEwen and A. M. Pereira of Gloucester, Massachusetts, 30 October 1940; converted to a coastal minesweeper by the General Ship & Engine Works, East Boston, Massachusetts; renamed Mockingbird 14 November 1940; and placed in service at Boston 12 June 1941. Struck from the Naval Register 29 July 1944, she was delivered to WSA for disposal at Little Creek, Virginia, 23 July 1945. Her subsequent status and fate are unknown.