This controllable and reversible propeller was apparently built for research under contract for the Engineering Division, United States Army Air Service at McCook Field. From 1918 to 1938, its designer, Frank W. Caldwell, effectively guided and set the pace of innovation in the American propeller industry. He oversaw all of the major developments in propeller design and construction-the metal, multi-piece propeller; the ground-adjustable-pitch propeller; and the hydraulically-actuated two-position controllable-pitch and constant-speed propellers-and was the first to make them practical.

The army created a government-business relationship that provided the true foundation for a modern propeller industry in the United States. Caldwell's move into industry in the late 1920s provided him the engineering and financial resources to create a practical and reliable modern variable-pitch propeller. The aeronautical community's challenge from 1918 to 1938 was to make the airplane go higher, faster, and farther. Creating propellers that were capable of "shifting gears in the air" was a remarkable achievement.