The autogiro is a rotary-winged aircraft with a freely rotating main rotor. Like helicopters, autogiros were capable of taking off and landing in shorter spaces than standard aircraft. The first successful autogiro flight was made by Juan de la Cierva in Madrid, Spain on June 9, 1923. In the U.S., W. Wallace Kellett, founder and president of the Kellett Aircraft Corporation (1929), built the first autogiro used by the U.S. Postal Service. The craft carried the mail between the Camden, New Jersey airport and the roof of the Philadelphia, Pennsylvania post office. The service speeded up mail delivery considerably, moving some local mail from overnight to same day service.
A series of "rehearsal" flights were made by the autogiro between Camden and Philadelphia before the official July 6, 1939 flight. The New York Times reported on July 3, 1939 that these rehearsal flights took only six and one-half minutes, as opposed to the time needed by mail trucks covering the same 40 to 45 mile route. Pilot John Miller flew the craft through its rehearsal paces.
The aircraft used in 1946 for the L.A. helicopter tests were six Sikorsky R-5Ds. Like the original Curtiss JN-4D aircraft of 1918, these helicopters were originally U.S. Army aircraft. The helicopters were used on tests along four routes in the L.A. area, all of which led to the L.A. airport. The routes' round-trip mileage ranged from 194 to 300 miles. The craft selected for the 1947 official trips were the Sikorsky S-51 helicopters. By early 1947, additional helicopter tests were being made both in Chicago and New York areas. On January 6, 1947, the first experimental helicopter flights were made in the New York City area. Nine helicopters were used for the tests, landing and taking off from thirty-nine sites in New York, New Jersey and Connecticut. In the first day of operation of the experimental service, over 100,000 letters (mostly philatelic collector's items) were carried by helicopter service. In a display of the community excitement over the prospective service, an article in the New York Timesnoted that crowds meeting the helicopters included "many boys and girls excused from school for the occasion."
Among the aircraft used in the New York experimental flights were the Sikorsky S-51, Firestone XR-9B, and Bell Aircraft B-47 helicopters. United Air Lines was the first scheduled airline to experiment with helicopter service, using a Sikorsky aircraft to carry passengers and mail in the Chicago area. By 1953, helicopters were beginning to experiment with nightly airmail service. On April 8, 1953 a helicopter flew 700 pounds of airmail from La Guardia Airport and Bridgeport, Connecticut between 4:25 a.m. and 5:05 a.m.