This is a commemorative cover promoting National Air Mail Week. Cancelled in Wilmington for an airmail flight to Woburn. Not sure if it ever went on a plane, but it sounded good right? Note the 6 cent stamp. In 1938 postage for a normal letter was only 3 cents, but would take over a week to travel across the country. For twice the price, it could get there in a few days. The USPS stopped "Air Mail" Service in the 1950's as domestic mail in the US was all done by air at that point.

The back is marked "Boston Mass, May 19, 1938, Air Mail Field.