Probably the first commercial application of aviation was carrying mail. Then as now, customers would pay a substantial premium for the swift delivery of an important message. But early aircraft navigation was primitive; With radio in its infancy and radar nonexistent, pilots had to rely on visual landmarks such as railroads and natural geographic features—and even then flight was practical only during daylight hours. Furthermore, a lack of distinctive landmarks—not to mention bad weather—could still lead to navigational errors. So, to expedite airmail delivery, a network of beacons was built…
