The Army bought this tiltrotor aircraft over 30 years before the Osprey flew

When the military adopted the V-22 tiltrotor aircraft in 2007, there were legions of naysayers who thought the military's first tiltrotor was too unsafe and too expensive to be added to the fleet.

But while the V-22 did have a spotted history during development, it wasn't the first military tiltrotor aircraft. A few such aircraft were in the early stages of development during World War II, and the U.S. Army bought a tiltrotor aircraft in 1956 — over 30 years before the first V-22 flew in 1989.

The Doak Model 16 was a vertical take-off and landing aircraft that used ducted tilt-rotors to generate forward thrust and — in the vertical flight mode — lift. Like the V-22, the Model 16 only rotated its rotors when transitioning between flight modes.

The Doak company spent years developing VTOL technologies before it sold a single Model 16 to the Army for further testing and development. For its part, the Army dubbed the Model 16 the VZ-4 and flew it for three years, evaluating its flight characteristics and the potential for full production and deployment.

Cobbled together with parts from other planes and using still experimental tiltrotor technologies, the VZ-4 had fairly impressive stats. It was capable of flying at 229 mph and had a 229-mile range.

But, the plane struggled with some "undesirable characteristics," especially during the transitions between vertical and horizontal flight. The most problematic was a tendency for the nose of the aircraft to rise in relation to the tail during the switch between flight modes.

Ultimately, the Army passed on purchasing more of the planes and loaned its single Model 16 to NASA for continued tests. When NASA was finished with it, the aircraft was sent to the Army Transportation Museum at Fort Eustis, Virginia.

Nowadays, the performance of the CV-22 and MV-22 Osprey has left little doubt that there's a place in the military inventory for tiltrotor aircraft. The Ospreys can fly from patches of dirt or relatively small ships at sea that traditional planes could never operate from. And they can fly for over 1,000 miles without refueling, over twice the range of the CH-47 Chinook helicopter.

These traits have earned the Ospreys spots in special operations units and Marine air-ground task forces around the world. And for the U.S. military, the road to tiltrotor aircraft all started with a single plane purchased in 1956.