Tech of the 9ast: Vought Sikorsky VS-300A
A little-known fact: Helicopters were more difficult to develop than airplanes. This 1939 Vought Sikorsky VS-300A was able to fly backward, side-to-side, up and down, and spin around but could not fly forward. The next model by Sikorsky was able to fly forward, however.
Photo by Wally Bahny for TechRepublic