Weter, on 06 March 2023 - 12:56 PM, said:
My too, but someone have pointed, that SW means "Switcher, having Welded frame" (instead of riveted)
SW was Six hundred horsepower Welded frame originally, but the option was SC for Six hundred horsepower Cast frame. I believe that it was GSC (General Steel Castings) who cast the frames but EMD pushed the welded frames as they could make them in house. The SC/SW used an 8 cylinder power unit. The more powerful switchers were NW/NC for Nine hundred horsepower with Welded or Cast frames, using a 12 cylinder power unit.
SW came to be just Switcher once they were all made with welded frames, the NW description was dropped and the different models were distinguished by the numerical part of the designation. It all got very messy as EMD changed the model numbering system a couple of times over the years as well.
If you can find a copy, the 'Diesel Spotters Guide' by Jerry Pinkepank is a very good source of information. I have a copy of the second edition, published in 1973, which I bought new when it first came out (and when I became a life member of the National Model Railroad Association - 50 years this year). The book is not always absolutely correct, but it's a good starting point.