Airmail is the transport of letters or parcels by airplane, which offers faster delivery than ground shipping. Originally, airmail was developed as a branch of the Army Air Service, created to ensure rapid delivery of important correspondence between New York and Washington, DC. Routes eventually sprang up across the country, and the Postal Service and private carriers began offering air service in addition to normal ground shipping.
The development of the airmail service played an important role in establishing commercial air travel in the United States. With planes traveling air routes repeatedly in order to transport mail back and forth, automated systems designed to aid in navigation provided the earliest framework for a national air traffic system. A transcontinental network of airports, instruments that allowed blind flying at night and radio-powered directional gear all made the lives of airmail pilots easier.
Airmail was a separate branch of the Postal Service up until 1975, when the service began routing mail by air whenever necessary or advantageous. Instead of paying specifically for air mail service, customers instead would select the speed at which they needed their parcels to travel, and the Postal Service would send the package by whatever means necessary for timely arrival. Some private companies still designate air mail service as one of their options, often for next day or second day delivery.