03/31/2022. Remarks by Johan Visschedijk: "The US Army's first rotary-wing aircraft (other than the service-financed De Bothezat and Berliner helicopters of 1921-1923) were autogyros tested for suitability as observation types.

One commercial Kellet KD-1 wingless autogyro ordered in 1935 as YG-1 (serial 34-278).

Kellett KD-1 YG-1A (36-352) (Johan Visschedijk Collection)

The YG-1 was followed by one YG-1A (36-352) and seven YG-IBs (37-377 to 37-382 and 37-635).

One YG-1B (37-378) became the YG-1C to test a constant-speed rotor and later became the XR-2; another YG-1B (37-380) became the XR-3.

Seven more Kellets similar to the XR-2 were ordered as XO-60 (42-13604 to 42-13610) in 1942; the first six became YO-60."