[2] The design did not go into full production, but over a dozen prototypes were used for various tests and projects.

Three prototypes were built, but serious rotor problems and complexity of mechanical systems precluded production.

Two prototypes were ordered as the XR-12, powered by a single 540 hp (403 kW) Pratt & Whitney R-1340-AN-1 radial engine and featuring seating for five.

[1] Another enlarged prototype (the XR-12B, Model 48A) with seats for eight plus two pilots and a more powerful 600 hp (447 kW) Pratt & Whitney R-1340-55 engine was also ordered, followed by ten pre-series YR-12B helicopters, with a glazed nose, instead of the car-like nose of the Model 42 and XR-12.

Related development Aircraft of comparable role, configuration, and era