Bidspirit auction | Worldwide Air Post Stamps and

Worldwide Air Post Stamps and Postal History - United States - 1918 (July 15), two First Flight covers Washington, DC - Philadelphia and New York - Washington, DC, the last one is reduced at left, each one franked by 16c green (new air mail rate started exactly on July 15), both mounted on page with detailed explanation, F/VF, Est. $600-$800, Scott #C2