The first stamp in history to depict an airplane was issued December 16th, 1912. Six years later, the Post Office Department issued stamps for airmail service.
The 20-cent stamp is part of the second set of the series depicting mail transportation and delivery methods. The stamp was available at post offices on January 1, 1913, and is found on a parcel front as a first day of issue. During the first six months of usage, the public and postmasters were confused about the specific requirement that these stamps be used solely for parcel post rates, and they were invariably used to pay regular postage rates. By July 1, 1913, the Post Office Department yielded, allowing all the stamps to pay the regular rates. This is the only series of stamps that can claim that distinction.