The Kellett Autogiro Corporation was formed in 1929 after it acquired a licence from Pitcairn-Cierva to build autogiros. The first three designed were all typical Cierva designs and the more advanced KD-1 was similar to the contemporary Cierva C.30. The KD-1/G-1 was the first practical rotary-wing aircraft used by the United States Army. The company stopped building autogyros in the late 1940s and switched to the design of helicopters. In the 1950s it built some ultra-light helicopters the RH-1 to test some rotor features and its last design the K-25 was an experimental convertiplane using tilt-rotors.