Arrows

On August 20, 1920, the United States opened its first coast-to-coast airmail delivery route, just 60 years after the Pony Express ended operations. There were no good aviation charts in those days, so pilots had to eyeball their way across the country using landmarks. Of course flying in bad weather was a challenge and often quite dangerous, and night flying was just about impossible. The Postal Service solved the problem with the world's first ground-based civilian navigation system; a series of lighted beacons that would extend from New York, City, New York to San Francisco, California. Every 16 km, pilots would pass a 21 m concrete arrow on the ground that was painted bright yellow. At the center of each arrow there would be a 15.5 m steel tower, topped by a million-candlepower rotating beacon. Below the rotating light were two course lights pointing forward and backward along the arrow. The course lights flashed a code to identify the beacon's number. If needed, a generator shed at the tail (or feather end) of each arrow powered the beacon and lights.