First flight cover is mail that has been carried on an inaugural flight of an airline, route, or aircraft, normally postmarked with the date of the flight often of the arrival destination proving it was actually carried on the aircraft and may have a special flight cachet.
Postmaster General James A. Farley and President Franklin Roosevelt created and proclaimed a week-long event to commemorate the 20th anniversary of the inauguration of US airmail service. They saw the event as an opportunity to gain wider support and usage of the Post Office Department’s airmail service. The celebration week was preceded by the issue of a new 6c airmail stamp, the attractive bicolored eagle, Scott #C23. Farley asked that every US citizen send an airmail letter during the week. The slogan was “Receive To-morrow’s mail today.”
Some of the cachets promoted the city's connection to baseball
