This was the prototype of the first mass produced helicopter and was then displayed in the Smithsonian Museum. It first flew on 13th January 1942 and the type saw action in WWII in May 1944

The prototype of the R-4, one of the first practical helicopters. It first flew on 14 January 1942.

This was officially accepted in May, 1942 and although not the first helicopter to see military service, the XR-4 was the first mass-produced helicopter and the first successful production rotorcraft of single-rotor configuration. The XR-4C came to the Smithsonian Institution in 1947 as part of a larger gift of aircraft transferred from the USAF to the new National Air Museum. It is now on display at the Udvar-Hazy Center.