By 1917, the U.S. government felt enough progress had been made in the development of planes to warrant something totally new - the transport of mail by air. That year, Congress appropriated $100,000 for an experimental airmail service to be conducted jointly by the Army and the Post Office between Washington and New York, with an intermediate stop in Philadelphia. The first flight left Belmont Park, Long Island for Philadelphia on May 14, 1918 and the next day continued on to Washington, where it was met by President Woodrow Wilson.
With a large number of war-surplus aircraft in hand, the Post Office set its sights on a far more ambitious goal - transcontinental air service. It opened the first segment, between Chicago and Cleveland, on May 15, 1919 and completed the air route on September 8, 1920, when the most difficult part of the route, the Rocky Mountains, was spanned. Airplanes still could not fly at night when the service first began, so the mail was handed off to trains at the end of each day. Nonetheless, by using airplanes the Post Office was able to shave 22 hours off coast-to-coast mail deliveries.