A byproduct of the training program was the creation of the American airmail system. On May 3, 1918, Col. Henry H. Arnold, Assistant Director of the DMA, was ordered to put together a daily route for moving mail by airplane between New York City, Philadelphia, and Washington, D.C. He assigned the task to the Executive Officer for Flying Training, Major Reuben H. Fleet. The Air Service, using six pilots (four instructor pilots and two new graduates) and six Curtiss JN-4H "Jenny" trainers modified to carry mail, began the mail service on May 15. It later extended the route to Boston and added Curtiss R-4LMs to its small fleet, carrying mail until August 12, 1918, when the U.S. Post Office took over.