This was the first compound helicopter to fly in the US. It used a coaxial rotor based on the Bendix Model J helicopter, with the rotor system modified and a propeller added on each side of the fuselage. The propellers were each powered by a 100 hp Continental engine, mounted on an outrigger. The propellers could be operated independently for yaw control. The 48 ft rotors were powered by a 450 hp Pratt & Whitney R-985 engine. In cruise flight, the cyclic pitch of the blades was significantly less than that required without the auxiliary propulsors. First flight was conducted at the end of November 1949.