Parcel post stamps were provided to cover the rates of postage on fourth-class
mail, established by the Act of Congress of August 24, 1912.

Less than a year later, on July 1, 1913, the Postmaster General directed that
ordinary postage stamps be valid for parcel post and that parcel post stamps be
valid for postage purposes and be continued on sale until the supply was
exhausted. The 20-cent value is the first U.S. postage stamp to depict an
airplane.