Few diesel locomotives have been more successful or influential than those of the American Locomotive Company (Alco) RS series. The first series, RS-1 (Road Switcher Type 1), was a revolutionary design that could perform any type of work and achieved great success in the export market. But the most popular was the RS-3, manufactured from 1950 to 1956, with 1370 built in total. The 1600-horsepower engine was powerful for the time, and resulted in a light, efficient, versatile engine that was easy to prepare and maintain. Road switchers, capable of both shunting and mixed-traffic trains, were exactly the type of diesel needed to compete with steam engines–and beat them. The RS-1 and RS-3 set the standard for American locomotive design, as most American goods engines nowadays are essentially larger, heavier road switchers.
This RS-3, Western Maryland Railway No. 195, may be found at the Baltimore and Ohio Railroad Museum.