This stamp is part of the first series of U.S. air mail postage stamps,
specifically issued to cover air-post rates.

The first experimental air mail flight in American took place September 23,
1911, between the two Long Island towns of Garden City Estates and Mineola. For
some years, such flights remained merely stunts to be performed at state fairs.

In 1918 the Post Office Department announced that an air mail service from New
York to Philadelphia to Washington, DC, would begin May 15.

The first stamp issued for that service was the 24-cent denomination, with the
16-cent denomination issued later in the year when rates were decreased.

Initial air mail service included a special delivery feature.  The 6-cent
denomination of the series was issued to pay the air-mail service only, without
special delivery.

Design of the three stamps is the same, featuring an army airplane because the
carrying of the mail had been entrusted to army pilots flying army planes.

The plane shown is known as the Curtiss Jenny, with "Jenny" coming from the
plane's official designation, which began with the initials "JN."