6c Orange, 1918 Air Post (C1).
Vertical pair paying 2c Postage and 10c Special Delivery fee on First Day Cover
posted locally in Washington D.C., stamps tied by partial Washington D.C. grid duplex, the clerk, evidently not satisfied with the clarity of the strikes, applied two more which clearly show the Dec. 10, 1918 First Day
date (the oval grid portion of one of these cancels also ties stamps), in addition, there is a Washington Post Office Special Delivery Department purple time/date handstamp on the back and clearly dated Dec. 10 (applied about 30 minutes after this letter was posted)
VERY FINE. THIS COVER WAS DISCOVERED BY US IN AN OTHERWISE MODEST CONSIGNMENT AND, ACCORDING TO OWNER'S PURCHASE DATE ON BACK, HAS NOT BEEN AVAILABLE TO THE MARKET FOR OVER 60 YEARS. A VERY IMPORTANT UNITED STATES FIRST DAY COVER, OF WHICH THERE ARE FEWER THAN FIVE KNOWN.
Accompanied by an American Philatelist article, "First Day Covers of U.S. 1918 Air Mail Stamps", by Ken Lawrence, which documents five 6c 1918 covers plus an additional three possible First Days.
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