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