The Kellett Aircraft was formed by W. Wallace Kellett and C. Townsend Ludington and their brothers, Rodney Kellett and Nicholas Ludington. In 1931, Kellett Autogiro licensed from the Autogiro Company of America, Juan de la Cierva's and Harold Pitcairn's patents for rotary-wing aircraft. 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.