Igor I. Sikorsky, engineering manager of the Vought – Sikorsky Division of the former United Aircraft Corporation, used the Stratford, Conn., sites to design, build, and test his innovative helicopter designs. Sikorsky’s VS-300 model helicopter was the world’s first design which used the now industry-standard single main rotor with an auxiliary anti-torque tail rotor. With the success of the first demonstration flight of the VS-300 on May 13, 1940, Sikorsky turned his attention to the design of his XR-4 prototype, which flew for the first time on January 13, 1942. The XR-4 became the first helicopter to enter military service when the U.S. Army Air Corps ordered 29 in January of 1943. It was also the first mass produced helicopter in the world, with the Vought – Sikorsky plant being the primary production site. Sikorsky’s success in demonstrating the helicopter as a viable design for commercial and military transport kicked off America’s “helicopter craze” in 1943, with hundreds of entrepreneurs seeking to imitate his designs.