Under Pitcaim-Cierva license developed and built autogiros at Philadelphia from 1929. A K-3 was taken to the Antarctic by Admiral Byrd on his second expedition in 1933, piloted by William S. McCormick. K-4 had two side-byside seats with demountable enclosure but retained wings. KD-1 of 1934 had tandem seats but was wingless and had direct-control rotor. In 1938 U.S. Army Air Corps bought seven Kellett autogiros for experimental use. From 6 July 1939 a Kellett KD-1 B of Eastern Airlines operated the first scheduled mail service by a rotary-wing aircraft, from the roof of the Philadelphia Post Office and the Camden airport. In 1939 Kellett exported an autogiro to Japan (see Kayaba). YG-1 was developed into XR-2 and XR-3 for the U.S. Army. XR-8 and XR-8A of 1943/1945 had twin sideby- side rotors. As Kellett Aircraft Corporation the company later undertook research and development contracts and subcontracting. Built its own KH-15 single-seat research helicopter (1954), the world's first rocket-driven helicopter. In late 1950s attempted unsuccessfully to resume production of pre-war KD-1 A direct-control autogiro.
Hughes owned Kellett designs.