Envelope from National Air Mail Week Addressed to Mr. & Mrs. Dean in St. Petersburg Florida from Mrs. Dean at 2 Park St. Pl in Arlington. Front has cachet by Sargent Stamp Albums of Arlington, MA of indian hunter figure with words "National Air Mail Week, Arlington Mass, May 15-21, 1938. Postmarked May 20, with a 6c air mail stamp. A cachet is a printed text on the left side of an envelope On may 15, 1918 the Post office flew the first "air mail" service in this country between New York and Washington, D.C. In 1938 the Post Office wanted to commemorate this event and to promote the use of air mail service by the general public. They planned a nationwide event for the week of May 15-21. They issued a new air mail stamp for teh occasion on May 14 (stamp on this envelope). The Post Office encouraged the postmasters to have local celebrations for this event and to provide cachets for envelopes presented during that week for air mail delivery. They also encouraged postmaster to arrange for special "first flights" involving as many post offices as possible, no matter what their size, for the day of May 19. In 1938 there were close to 40,000 post offices in the U.S. and there are probably cachet covers from between 15 and 20 thousand different cities.