The commercial aircraft industry developed in the 1930s at a time when Alcoa was a true monopoly and the sole source of supply of aluminum in America. America was a world leader in developing commercial aircraft. This image is of the Douglas DC-3, a fixed-wing propeller-driven airliner. Its speed and range revolutionized air transport in the 1930s and 1940s. Its lasting impact on the airline industry and World War II makes it one of the most significant transport aircraft ever made.