Sikorsky R-4 helicopter model. Developed by Igor Sikorsky from his famous VS-300 experimental helicopter, the R-4 became the world's first production helicopter, and the U.S. Army Air Force's first service helicopter. The prototype XR-4 made its initial flight on Jan. 13, 1942, and as a result of its successful flight tests, the USAAF ordered three YR-4As and 27 YR-4Bs for service testing and flight training. Of these, one went to Burma and one to Alaska, while several others were assigned to the U.S. Navy, U.S. Coast Guard and British Royal Navy. They showed such promise that the USAAF ordered 100 R-4Bs.