After World War Two, ALCO recognized the market for a more powerful road switcher than it's 1000 h.p. RS-1. In 1946, the first 1,500 h.p. RS-2 was delivered to the Detroit & Mackinac.

Alco went on to build some 366 of these work horses to 46 different North American and foreign roads and private companies between 1948 and 1950.

Define "road switcher"; minimum of 900-hp, along hood for the engine, a short hood for steam-generating equipment, the ability to handle freight or passenger assignments. Define it as you will, many give credit to Alco for the "first" road switcher, the RS-1. The RS-1 was the first of the early generation of Alco road switchers, soon followed by 1,500/1,600 horsepower RS-2s and RS-3s. Also followed were six-axle versions, the RSCs and RSDs.