Today, gyrocopters are mostly found in the homes of hobbyist collectors and in James Bond films. Because of the effectiveness of helicopters, these odd, single-person aircrafts with blades reminiscent of windmills have limited practical use. But this was not always so: soon after the invention of a gyrocopter prototype—the autogyro—in the early 1920s by Spanish engineer Juan de la Cierva, the machines showed the potential to revolutionize transportation.

One place where they tried to leave their mark? Mail delivery.

Though autogyros could neither fly long distances nor at high speeds, they avoided car traffic and required small runways (between 15 and 50 feet), making them ideal for efficient, small-scale transportation. Unlike planes, which struggled to fly at low speeds except at sharp angles, autogyros also did not stall.

Sensing opportunity, the United States Postal Service—then the U.S. Post Office Department—decided to invest in the new technology. In 1937, Congress appropriated money to fund a series of experiments on autogyro mail delivery, and within a year the first flight—from Bethesda, Maryland to Washington, D.C.—was made.

Apparently, the test was effective: in January 1939, the U.S. Post Office Department began considering offers from commercial airline companies for a Philadelphia-based autogyro postal service. The video above shows an early autogyro flight from Philadelphia, Pennsylvania to Camden, New Jersey—a six-minute trip.

Autogyro tested to deliver the mail in Washington, D.C., 1938 Library of Congress/LC-DIG-hec-25025

To deliver the mail, autogyros could simply land on the roof of a post office, drop off the mail to a waiting employee, and then fly to the next location. During the 10 years in which autogyros were delivering U.S. mail, hundreds of flights hopped from roof to roof in cities like Camden, Philadelphia, and Washington—as well as Chicago, Illinois and New Orleans, Louisiana. In all, they delivered thousands of pieces of mail.

But by the late 1940s, as helicopter technology improved, the autogyro mail service fell out of favor. Unlike helicopters, autogyros could not hover—a significant technical problem.

Today, the memory of the autogyro delivery service lives on through the special stamps that christened the letters they delivered.

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