Igor Sikorsky, born in Kyiv (Ukraine, then Russian Empire), trains at the Kyiv Polytechnic Institute and emigrates to the US in 1919, fleeing the Bolshevik revolution. On 14 September 1939 he makes the first flight of the VS-300 in Stratford (Connecticut), the first helicopter with a main rotor and auxiliary tail rotor configuration that becomes the universal standard. Corradino D'Ascanio (Italy, 1930) had built a coaxial double-rotor prototype that broke altitude and duration records but whose design did not scale; Sikorsky's tail rotor solves the reaction-torque problem practically and reproducibly. The Sikorsky R-4 (1942) was the first mass-produced helicopter in history, used by Allied forces in World War II.