While other railroads switched from coal to diesel, the C&O refused to take this step for a while. Given their huge coal business, attempts were made to modernize the fleet while retaining coal as fuel. In 1948 and 1949, a total of three coal-fired steam turbine locomotives were built, which were the longest single-unit locomotives in the world and were nicknamed “Holy Cow”.

In the front part of the locomotives was the coal bunker, which fed the 6,000 hp turbine in the rear part of the locomotive. The water came from an additional tender. The eight traction motors were powered by the four generators, which together delivered 4,960 hp. With this system it was hoped that maintenance would be easier than with piston steam locomotives and the aim was to complete round trips of 1,000 miles without servicing stops.

The intended area of operation was the planned “Chessie” streamlined train. With a top speed of 100 mph (161 km/h) of the locomotives, this was to be hauled at a cruising speed of 70 mph (113 km/h). The M-1's fate finally came when they turned out to be very unreliable and the “Chessie” did not come into being. They were eventually used in other areas for only a short time and were scrapped in 1950.