During the Young era and following, C&O was headed by Walter J. Tuohy, under whose control the ""For Progress"" theme continued, though in a more muted way after the departure of Young. During this time, C&O installed the first large computer system in railroading, developed larger and better freight cars of all types, switched (reluctantly) from steam to diesel motive power, and diversified its traffic, which had already occurred in 1947 when it merged into the system the old Pere Marquette Railway (PM) of Michigan and Ontario, Canada, which had been controlled by the C&O since Van Sweringen days. The PM's huge automotive industry traffic, taking raw materials in and finished vehicle out, gave C&O some protection from the swings in the coal trade, putting merchandise traffic at 50% of the company's haulage.