GE's history of working with turbines in the power-generation field gave them the engineering know-how to move into the new field of aircraft turbosuperchargers.[citation needed] Led by Sanford Alexander Moss, GE introduced the first superchargers during World War I, and continued to develop them during the Interwar period. Superchargers became indispensable in the years immediately prior to World War II, and GE was the world leader in exhaust-driven supercharging when the war started. This experience, in turn, made GE a natural selection to develop the Whittle W.1 jet engine that was demonstrated in the United States in 1941. GE ranked ninth among United States corporations in the value of wartime production contracts. Although their early work with Whittle's designs was later handed to Allison Engine Company, GE Aviation emerged as one of the world's largest engine manufacturers, second only to the British company, Rolls-Royce plc.