The Sirowsky R-4 helicopter was developed for the US Army Air Force and performed its first combat rescue in April 1944 in the Burma theater.
Thirty R-4s were ordered and several performed search and rescue operations from Tinian Island in the Pacific to rescue B-29 crews during takeoff and landings by the accident prone heavy bomber.
(http://i941.photobucket.com/albums/ad256/waldoegray/R4-sketch_zps3e86c22e.jpg) (http://s941.photobucket.com/user/waldoegray/media/R4-sketch_zps3e86c22e.jpg.html)