Entitled: "Join the air service and serve in France - Do it now". Poster showing two soldiers, one using binoculars, in foreground, and American airplane above. The Air Service, United States Army was a forerunner of the United States Air Force during and after WWI. In France, the Air Service of the American Expeditionary Force began combat operations in the spring of 1918. Artist Paul J. Verrees, 1917.