The World Wars brought heavy demand to the L&N. Its widespread and robust network coped well with the demands of war transport and production, and the resulting profits harked back to the boost it had received from the Civil War. In the postwar period, the line shifted gradually to diesel power, and the new streamlined engines pulled some of the most elegant passenger trains of the last great age of passenger rail, such as the "Dixie Flyer", the "Humming Bird", and the "Pan-American".