 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

Assigned to the 3rd Naval District, "Idalis" served as a patrol craft in Long Island Sound and as training ship for officers at the Naval Reserve Training School Pelham Bay Park at Pelham Bay Park, New York, until the close of World War I.