1973 Progress In Electronics 11¢ Airmail Stamps

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. Special postage stamps were issued for use with this service. Domestic air mail became obsolete in 1975, and international air mail in 1995, when the USPS began transporting First Class mail by air on a routine basis. All post-1977 United States stamp images are copyright of USPS. Scott cataloged stamps received a "C" designation for airmail issues. Designated for international mail, and showing a small airplane, the January, 2012 $1.05 Scenic America series issue was designated C150. 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". Thus a regular series Scott number, 4740, was designated.