Sikorsky R-4

R-4 / Hoverfly
A Sikorsky R-4 in a hover
Role	Helicopter Type of aircraft
Manufacturer	Sikorsky Aircraft
Designer	Igor Sikorsky
First flight	January 14, 1942
Introduction	5 January 1943
Primary users	United States Army Air Forces United States Coast Guard Royal Air Force
Produced	1942–1944
Number built	131
Developed from	Vought-Sikorsky VS-300
Developed into	Sikorsky R-6

The Sikorsky R-4 is a two-seat helicopter that was designed by Igor Sikorsky with a single, three-bladed main rotor and powered by a radial engine. The R-4 was the world's first large-scale mass-produced helicopter and the first helicopter used by the United States Army Air Forces,^[1] the United States Navy, the United States Coast Guard and the United Kingdom's Royal Air Force and Royal Navy. In U.S. Navy and U.S. Coast Guard service, the helicopter was known as the Sikorsky HNS-1. In British service it was known as the Hoverfly.