The R-4 was the world's first large-scale mass-produced helicopter and the first helicopter to see service with the USAAF and others (USN, RAF, etc.). This example was TOC in April 1944 with the USAAF and at the end of WWII became N92820 with United Aircraft Corp and used for testing by Sikorsky. This registration was cancelled in October 1955 and the helicopter had become part of NEAM by August 1994. This isn't the nicest of photos but it shows nicely the difference between the conventional drive-shaft driven rotor on the R-4B and the hingeless rotor of the Doman YH-31 in the foreground.

Used for search and rescue. Photo from: National Archives at College Park, Maryland

The USAAFS Thomas LeValley was a Liberty ship converted to a floating Aircraft Repair Unit. It was renamed the Major General Walter R. Weaver in April 1945. The helicopter was attached to the ship for ship-to-shore transport. The fate of the helicopter not known but the ship was stored after war until scrapped in 1970. Photo from: National Archives at College Park, Maryland

This helicopter was urgently flown to Burma (Myanmar) in a C-54 to rescue the crew of a downed B-25. It eventually crashed in Burma on July 26, 1945. Photo from: National Archives at College Park, Maryland

Ex N68351, expired in 2013. This R-4B is now on display at the US Army Aviation Museum at Fort Rucker, Alabama.

Preserved wearing early WW2 colour scheme

The R-4 became the world's first production helicopter and the USAAF's first service helicopter. This R-4B on display at the National Museum of the USAF was donated to the museum by the University of Illinois in 1967.

Ex US Army 43-46560. I believe this to be the only R-4 ever modified as a crop duster in the U.S.