In order to compete with United Airlines, TWA commisioned an aircraft from Douglas Manufacturing. Douglas had to design an aircraft that could fly over the Rockies on only one engine. Douglas's chief designer convinced Charles Lindbergh the technical advisor of TWA to try the Douglas design. The DC-1 was the first plane to use the "monocoque" design where the weight of the plane and wings are borne by the entire skin. The plane was also the first to have a two speed propellor.