U.S. Airmail Stamps
The first airmail route in the United States was over the 200 mile distance between New York and Washington, D.C., with a stop in Philadelphia. One round-trip flight was flown each day except Sunday. For the first few months, the airmail service was a joint effort of the War Department, which provided the planes and pilots, and the Post Office Department, which handled the mail.
By September of 1920, airmail service routes existed from New York all the way to San Francisco. To support this new, premiun service, special air post stamps were issued beginning in 1918 and concluding in 2012. The modern air post issue do not have 'airmail' printed on their face, but do carry a small airplane silhouette and are franked for specific international airmail rates