This story originally appeared on Feb. 15, 2015. During the Korean War, quite a few American pilots went down behind enemy lines. Some got...

During the Korean War, quite a few American pilots went down behind enemy lines. Some got lucky and escaped with the help of daring airborne-search-and-rescue crews, while others never made it home alive.

The U.S. Marine Corps looked to helicopters to help rescue downed pilots. After a modest debut during the last months of World War II, the whirlybirds proved themselves in Korea as transports and spotters.

But rescue crews aboard their slow, underpowered choppers risked becoming targets and captives themselves. What if downed pilots could rescue themselves … with their own helicopters?

A chopper small enough to drop from a fast aircraft, and easy enough for a pilot to assemble and fly. Such a helicopter could also prove useful for reconnaissance.

With these concepts in mind, the Marine Corps requested bids in 1954 to develop a collapsible, personal helicopter. The Hiller Aircraft Corporation of Palo Alto, along with another firm, won the contract.

Stanley Hiller counts as one of the fathers of the American helicopter, along with Igor Sikorsky and Frank Piasecki. Hiller designed and flew his first rotary-wing craft at the precocious age of 17, despite never having flown before.

His company built some of the first helicopters for the U.S. military.

Hiller had already designed pint-sized choppers. The HOE-1 Hornet — a two-person aircraft only 24 feet long and weighing 544 pounds, employed a novel propulsion technique.

Tiny ramjets mounted on the blade tips spun the machine’s rotor at flight speeds. These ramjets let Hiller build a smaller, lighter helicopter.

Willy Turner of the Hiller Aviation Museum showcases the Rotorcycle. Video via War Is Boring

But Hiller Aircraft’s design for the Marines was a marvel of engineering. The “Rotorcycle” weighed just 300 pounds. When disassembled, it was small enough to fit inside a 13-foot-long casing shaped like a bomb.

No tools included … or required. Its parts either folded out or attached with large pins. Assembling the machine only took a few minutes.

When deployed, a Rotorcycle could fall from a plane to a downed pilot behind enemy lines. After recovering the ’copter capsule, the pilot could assemble the machine, mount up and fly away to safety.

The Rotorcycle’s 45-horsepower, two-stroke engine spun an 18-foot-diameter rotor with enough power to lift the machine and its occupant 10,000 feet high. It could travel at more than 50 miles per hour.

The aircraft’s 40-mile-range was supposed to get the pilot back to friendly territory.

Hiller Aircraft built the first prototype, but found its hands full with other helicopter projects. The company contracted production out to Britain’s Saunders-Roe, a venerable and talented aircraft firm familiar with building unusual aircraft.

Saunders-Roe built 10 of the collapsible YROE-1 helicopters. The company sent five sent back to the United States for testing and evaluation. The others remained in Europe for testing and marketing.

Above—1950s-era magazine illustration of hypothetical combat use of Rotorcycles. Illustration via David Zondy. At top—Hiller YROE-1 undergoing flight tests, NASA Ames Research Center, 1963. NASA photo

The strange little birds made quite an impression. Even before the military began testing them, the notion of a one-person portable chopper delighted the public.

In 1957, Stanley Hiller tried to dampen civilian enthusiasm, telling the United Press news agency, “It will be a long time before the average citizen may own one.”

He knew what he was talking about. Flying machines are inherently more complicated to operate than ground vehicles, and the consequences of error or malfunction are much greater—because of gravity.

There’s a common expression that flying a helicopter is like patting your head while rubbing your belly and driving with your knees. It takes a lot of training to become a safe, skilled chopper pilot.

And that was the Rotorcycle’s biggest drawback. You not only needed to be a helicopter pilot, but a good one to fly it. Add sensitive controls and a bicycle-seat cockpit—with few visual cues—and you got a very tricky aircraft to operate.

You also had an aircraft that was quickly becoming obsolete. The Rotorcycle’s mission evaporated when helicopters acquired powerful gas-turbine engines and search-and-rescue techniques improved.

Five of the tiny choppers now sit in museums, including the Hiller Aviation Museum in the San Francisco Bay Area and the Smithsonian’s Udvar-Hazy collection in Washington, D.C.

The rescue of downed pilots behind enemy lines is still a problem for militaries, especially when captured pilots become pawns for governments or terrorist group. And for sure, small flying machines portable enough to pack in a trunk maintains their allure.

Except today, we don’t need the human pilot. Instead of sending soldiers into battle with personal helicopters strapped to their backs, we can simply send in the drones.