Sikorsky R-4B Hoverfly: The US Army Air Force’s 1st Helicopter

The Sikorsky R-4, one of the world’s first mass-produced helicopters, became a pioneering design that helped set the stage for generations of development of military helicopters. The aircraft was initially developed by Igor Sikorsky during the Second World War and featured a single primary rotor with three blades that was powered by a practical and easy-to-fix radial engine.