In 1918 the United States issued a philatelic set of six, 16 and 24 cents stamps for use on air mail letters. The 24 cents stamp was printed in blue and carmine, which required printing from two separate plates, one for each colour. In error, one of the sheets of 100 stamps was printed with the blue aircraft upside down.

This stamp is one of the most famous errors in American philately, and is one of the most highly prized objects for philatelists.