VS-300.
In 1939, Sikorsky and a team of his engineers designed the VS-300. The VS stood for "Vought Sikorsky" and the 300 indicated that it was Sikorsky's third helicopter design. Vs300 had a 75 hp Franklin 4 cylinder engine. The basic structure was the heavygauge welded steel tubes. It had no covering at all and no instruments. It had a three bladed main rotor and the anti-torque rotor at the rear.