Domestic U.S. Air Mail was established as a new class of mail service by the United States Post Office Department (POD) on May 15, 1918, with the inauguration of the Washington–Philadelphia–New York route.
[3][4] All post-1977 United States stamp images are copyright of USPS.
[5] Scott cataloged stamps received a "C" designation for airmail issues beginning in 1940.
However, with the January, 2013 issue of the $1.10 Global Forever Stamp no specific airmail purpose was shown in the design.
Rather, the Postal Service stated that this "stamp offers a single price for any First-Class Mail International 1-ounce letter to any country in the world.