From the archives of the Smithsonian Institution and the National Postal Museum:

In the 1930s, U.S. postal officials tried different ways of moving the mail. One technique was called "skyhooking," which brought the mail to rural towns that had no adequate railway or highway mail routes.

Outgoing mail was placed in rubber containers, like the one below, and attached to 15-foot-tall metal posts. Pilots flying tight-turning airplanes would position the plane to hook the outgoing mail container using a 60-foot grappling hook on the airplane's tail.

On May 12, 1939, the first scheduled service began flying two experimental routes led by the All American Aviation Co., now known as U.S. Airways. The airline dropped its pickup operations in 1949 and converted to carrying passengers.