The ALCO S2 and S4 were diesel/electric switchers manufactured by the American Locomotive Company (ALCO) and Montreal Locomotive Works (MLW). The S2 and the S4 differed only in trucks, with the S-2 using ALCO’s own “Blunt” trucks, and the S-4 riding on standard AAR type A switcher trucks. Both were powered by ALCO 539 turbocharged, 6-cylinder diesels with 1000 horsepower. 1502 S-2s was built between August 1940 and June 1950 and 797 S-4s were constructed between June 1949 and August 1957 (MLW until 1957). Canadian production of the S-4 started more than a year before U S production of the S-4. ALCO did not start building the S-4 until August 1950.
A few S4s are still in service on shortline railroads around the US. Several are preserved in US and Canadian museums.
The Erie Lackawanna was formed in 1960 and used S4s. For more information about the EL railroad go to American Rails at http://www.american-rails.com/erie-lackawanna.html
Erie Lackawanna No. 528
The Chesapeake & Ohio used Alco S4s. Here is a video of repainting the C&O 5109 at https://www.youtube.com/watch?v=kk27z0VzQes The Toledo, Lake Erie & Western Railroad Museum in Grand Rapids, OH restored the C&O 5109. For more information go to http://tlew.org/
Micro-Mark sells several Alco S4 model trains at http://www.micromark.com/search?keywords=Alco%20S4