Here are some photos I took of the sole remaining Kellet KD-1A Autogiro on display at the Yanks Air Museum in Chino. There was another variant (the Kellet K-2 Autogyro) on display at the NMoUSAF.
Built in the 1930s, the KD-1 was the first practical rotary-wing aircraft used by the United States Army and inaugurated the first scheduled airmail service using a rotary-wing aircraft.