USS Idalis (SP-270) was a United States Navy patrol vessel in commission from 1917 to 1919. Idalis was built as a civilian motor yacht in 1908 by the Gas Engine and Power Company at Morris Heights in the Bronx, New York. Sources differ as to her original name; she either was built as Idalis and later was renamed Amalia IV, or was built as Amalia IV and later renamed Idalis. The U.S. Navy purchased her from her owner, Carl Reinschild of New York City, in June 1917 for World War I service. She was commissioned on 25 August 1917 as USS Idalis (SP-270) -- that name representing the Navy either retaining her existing name or reverting her from Amalia IV to her previous name—with Lieutenant G. C. Fry, USNRF, in command