This 1948 card commemorates the beginning of United States Air Mail Service thirty years earlier on May 15, 1918. The stamp on the card is the then-current 5-cent Air Mail stamp, which was cancelled on May 15, 1948 at the National Airport Station in Washington, D. C.
This stamp is the 5-cent DC-4 Skymaster stamp issued on March 26, 1947. The domestic airmail rate had been reduced from eight cents per ounce to five cents per ounce on October 1, 1946. This stamp was issued in a small format for two reasons, user convenience and as cost saving.
The back of the card has a cachet showing the first air mail route from Washington to New York with a stop in Philadelphia. The first northbound flight turned out to be less than successful. You can read about it here.
This is a post for Sunday Stamps at Viridian's Postcard Blog