The Pennsylvania Railroad bought 22 RS-1's in 1950, 2 in 1951, and 2 in 1952, and one notable exception - the road number 5906. It was built in December of 1948. This one switcher was a tester for the PRR to see if they liked them. The unit was classified by the PRR as an "AS10s" (Alco, switcher, 1000 horsepower). In general, the "RS" stands for "Road Switcher". These locomotives were normally used for freight service, but could later on be found in commuter service as well. The design heritage comes from Alco's S2 switchers by adding a short hood behind the cab (Model Railroader Magazine, Nov. 1987, pg43). This magazine article also includes a photo of #5620 taken in 1955. The prototype photo of $8485 came from the Fallen Flags web site. There are additional references in the book "Pennsylvania Railroad" (1997, MBI Publishing Company, ISBN 0-7603-0379-7, pg 37), and "Pennsylvania Railroad Diesel Locomotive Pictorial Volume 1 - ALCo RS Series" (1995, Withers Publishing, ISBN 1-881411-05-2, pp 7-14).

This is by far my most favorite type of locomotive. As a matter of fact, after purchasing the starter set in 1999, my first addition was a Gulf, Mobile, & Ohio RS-1. At the time I didn't know that I was going to model the Pennsy. I later on bought these Atlas PRR models. After I bought the first one, I had the frame milled by Aztec for conversion to DCC. I was not happy with their work for two reasons (the workmanship, however, was fine). The milling assumes the sacrifice of one of the headlights. That is fine, but they decided to sacrifice the headlight in the long hood. Unlike other railroads, the PRR ran their RS-1's with long hood forward. Secondly, the amount of milling removed was enough for one of the older, larger N-scale decoders. The Z-scale decoder I wanted to put in it is much smaller. After an unsuccessful attempt at doing the conversion to DCC, I abandoned the project (it was my first attempt at converting a locomotive to DCC - not exactly a starter project). In 2003 Atlas re-released a number of RS-1 models. I bought the one PRR model they made. Then later on I saw another road name model available at a very attractive price, so I came up with the idea of buying a second model and simply swapping the shell with the older PRR shell I had left over from the first RS-1 model. A parts list for the Atlas RS-1 is available on the Web.