The Sikorsky R-4 was the first helicopter to go into mass production for the US armed forces (and a few for Britain’s Royal Air Force). Between 1942 and 1944, 131 were built.
The aircraft was announced to the public in 1942. It was the first time most people had ever heard the word ‘helicopter’, and the aircraft’s capabilities were, at the time, extraordinary. Here’s the first publicity film of the R-4.
The R-4 saw combat in Burma, where it was used for combat rescue and casualty evacuation from the thick jungle. You can read about its first combat rescue mission here. It also made the first helicopter landing on a ship, in trials aboard the British merchant ship Empire Mersey in 1944.
The R-4 wasn’t very successful, being grossly under-powered, but it was the first of its kind. More and better successors would build on the foundation it laid.