By the 1920s, it was clear that getting a heavier-than-air craft to fly was only the first problem to solve for aviation to be successful. The next, and perhaps larger, hurdles were navigation and communication.
Once a pilot and his or her airplane are aloft, getting from point A to point B requires knowing how to get there and what obstacles must be avoided, including terrain and weather.
Beacons
The challenge of flying in the dark needed to be solved because of the success or air mail largely depended on being able to continue the transport of mail through the night. The original, impromptu techniques of lighting bonfires and shining automobile headlights at landing strips were not a permanent solution.
In 1925, the Post Office Department received funding from Congress to install a series of beacon lights from Chicago, Illinois to Cheyenne, Wyoming. These lights were mounted onto 50-foot towers. By 1927, the Post Office Department had erected 616 air mail beacons between New York and San Francisco.
Boundary Light
Cone-shaped boundary lights like these were installed at the corners of air fields. The cones were mounted on galvanized pipe, several inches off the ground -- or more, in areas with heavy snow.
Rotating Beacon
A variety of rotating beacons were employed to guide pilots at night. This 24" (61 cm) double light would have been mounted on a tower, roughly 50 feet (15 m) high. Rotating beacons were placed along major routes at 10-mile (16-km) intervals.
Tripod LightLittle is known about this mid-20th century portable boundary light. It features adjustable legs to vary its height and a Fresnel (pronounced freNELL) lens. A Fresnel lens focuses light like a convex lens but with less, and thus lighter, glass.
Radios
In 1920, the Post Office Department ordered radio stations installed at each of the planned transcontinental airmail fields. Originally, most of the radio communication occurred between the airfields themselves but not between airfields and pilots. Although successful tests had been done as early as 1917, radios in airplanes would not come into use until the late 1920s.