[First flight air mail cover addressed to William E. Boeing from Glenn L. Martin Company, July 3, 1942]

First flight air mail cover addressed to William E. Boeing, Seattle, Washington, from the Glenn L. Martin Company, Baltimore, Maryland, July 3, 1942.

Stamped cachet: "First Flight - This cover carried on first official flight of the 'Mars,' built by the Martin Co. for the U.S. Navy - World's Largest Flying Ship."