The Sikorsky-designed R-6A two-seat observation helicopter evolved from the boxy R-4, the first Air Force helicopter to serve in a combat zone (example here). Although Sikorsky built the first six for testing, another 219 were constructed under licence by Nash-Kelvinator, this being one of them. Accepted by USAAF at Detroit in April 1945, it operated with various training units in Texas till declared excess in March 1949. Acquired by the museum in 1986