https://flic.kr/p/6Tvfgq | Allied aircraft demonstration at polo grounds 1917 | Washington, D.C., circa 1917. "Allied aircraft demonstration at polo grounds. Avro training plane designed by A.V. Roe of England. Lieut. Stephen Bonsal Jr., one of the young Army flyers who have entered the newest profession, that of airplane mail carrying, is the son of the former war correspondent and veteran newspaperman who is now a major attached to the general staff of the Army." Harris & Ewing C