The Sikorsky H-5, (aka R-5, S-51, HO2S-1, HO3S-1) (R-5 until 1948; company designation VS-327) was a helicopter built by Sikorsky Aircraft Corporation, formerly used by the United States Air Force, and its predecessor, the United States Army Air Forces, as well as the United States Navy and United States Coast Guard (with the designations HO2S and HO3S). It was also used by the United States Post Office Department.