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.