Ya got to be careful not to get me started on the subject of switchers. Here's why....
Diesel electric locos in America were developed in the 1920's. There were some early European prototypes but the Diesel electric took off in America. The early production diesel switchers were boxcabs, initially as joint ventures between GE, Westinghouse, Ingerstoll Rand, Alco and GM. These companies went their own way with they particular line of switchers in the 1930's. Early Alco switchers looked like this:
http://en.wikipedia.org/wiki/ALCO_boxcab
The 'high hood' series followed. Railfans call them HHxxx (horse power rating, eg HH600), but Alco didn't have a series name at this time.
http://en.wikipedia.org/wiki/ALCO_HH_series
The S series followed from 1940 with the S-1 (700 hp) and S-2 (1000 hp). These had blunt trucks but their 1950's successors had the AAR trucks. These were the S-3 and S-4 replacing the S-1 and S-2 respectively.
The RS series was developed from the S series also, which inspired EMD to develop the GP locomotives in response. Later Alco switchers inclue the S-5 and S-6, which look similar but significantly different to the earlier S switchers, the T model and finally a century series switcher (C415).
http://en.wikipedia.org/wiki/ALCO_T-6
http://en.wikipedia.org/wiki/ALCO_Century_415
There were some Alco swithcers produced in Canada also, which look much like the basic S series switchers. I think they are classed as S-12.
Of these the S series is most commonly produced in model form. Apart from AHM, Atlas has done the S-1 through S-4 several times over (the latest looking so tempting that I might buy another Alco switcher or two). Atlas has done two runs of the HH660 over the last few years.
Lifelike/Walthers has done the S-1 and S-3 in their P2K range, out of production but still common on the market.
Now Bachmann has produced the S-2 and S-4.
There are various old kits and brass models of the main S series switchers as well.
Apart from the Atlas HH600, one must hunt down brass models for other Alco switchers. Oh, I think there is a C 415 in plastic, maybe by AHM.
OK, that should cure any problems you had with insomnia.
