The first variable-pitch propeller developed in the United States took to the air over southern California as America entered World War I in April 1917. Pioneer aviator Earl S. Daugherty flew his Daugherty-Stupar Tractor biplane with a variable-pitch propeller designed by Los Angeles inventors Seth Hart and Robert I. Eustis (Figure 7). Starting off with a low pitch setting for high thrust, he gradually increased the pitch of the propeller to generate more speed as the plane leveled off over the airfield. Daugherty was “very much impressed” with the propeller's effect on his airplane's performance. The new propeller was controlled manually by the pilot, meaning that it relied on a series of mechanical linkages and the strength of the pilot to change the pitch. Daugherty's flights were the American propeller community's first steps toward developing a practical variable-pitch mechanism. That work, combined with the efforts of other experimenters in North America and Europe, met varying degrees of success between 1917 and 1927.

World War I served as a catalyst for the reinvention of the airplane in Europe and the United States, but the path and direction that new technology would take, as well as the nature of the organizations that used it, were not clear. In the United States, the newly created Army Air Service was at a crossroads regarding the primary role of military aviation in the postwar period. A tension existed between the old Army leadership, who favored using airplanes in a supplementary tactical role, and the youthful Air Service officers who sought to create an entirely new military doctrine based on strategic bombing. As this internal battle played out, the Army Air Service's strategy was to focus on wide-ranging improvements that enhanced the speed, range, load, and maneuverability of observation airplanes, bombers, fighters, transports, trainers, even airships. One of the key technologies for the service's future airplane – no matter what its role – would be the propeller.

The aeronautical community was aware of the potential value of controllable and reversible variable-pitch propellers. Controllable-pitch mechanisms offered enhanced operating performance and fuel economy at the different operating regimes of takeoff and cruise for both single- and multiengine aircraft.