 On July 25, 1918, Harris along with co-pilot George Lewis, led the first successful flight by American pilots over the Alps, crossing from Italy to France in four Caproni bombers.While based in Italy Harris also helped the United States Navy establish an aerial ferry route from Milan to Paris.Following the conclusion of World War I, in September 1918 Harris was recalled to the United States and assigned as a test pilot at Wilbur Wright Field in Dayton, Ohio.