I was curious what the SW stands for in the SW series locomotives, such as SW7, SW1000, SW1500?
Thanks for any info.
Mark
Switcher.
To quote from the April 2000 issue of MR (p 16):
“In a more logical locomotive naming universe, you might assume that the SW designation stood for ‘switcher’, but in fact the S stood for 600, the engine’s horsepower rating, and the W stood for Welded frame (as opposed to C for Cast)”
Hope this answers your question.
Cheers,
tbdanny
Switcher, Welded Frame.
So NW, as in NW2 stands for ??? (nudger?), welded frame?
Yes, exactly. N = 900 h.p.
SW1 = Six hundred hp, Welded frame.
NW1 = Nine hundred hp, Welded frame.
But that’s how far the initial naming standard goes - the NW2, NW3 and NW5 had a 1000 hp engine rather than a a nine hundred hp engine.
And you get stuff like NW1 and NW2 were diesel switchers, while the NW3 and NW5 (which were only produced in a handful of units, rather than the 1000+ NW2 units produced) were passenger terminal switchers (with steam generators).
As for the SW’s, the SW7, SW8, SW 9, SW1000, SW1001, SW1200 and SW1500 did not have a six hundred hp engine (the SW600 did).
Here we can start thinking we understand the system again, SW now meaning SWitcher, and we can observe that the SW8 had an eight hundred hundred hp engine, the SW1000 a 1000 hp engine, the SW1200 a 1200 hp engine, the SW1500 a 1500 hp engine. And the SW600 had a 600 hp engine.
So far, so good. And then we notice that the SW7 and SW9 did not have a 700 hp and 900 hp engine - they both had 1200 hp engines. And the SW1001 was a special case, too - SW1000 engine and hood, SW1200 frame, cab and steps.
The TRs were cow-calf combinations, intended as TRansfer engines - ie engines that needed more weight on their drivers to get long cuts of cars going, but did not need to move all that fast. The TR’s were based on various NW or SW engines.
Basically, model names tended to start out being reasonably descriptive, but that quickly broke down, when the marketing people took over - “we have some changes - let’s give it a new model number!” 
Grin,
Stein
Your answer rings true for the original end-cab switchers from the 1930s but by the time the SW7 reared its head in the late-'40s EMD had long-since changed the meaning of “S” from 600–they would produce one last 600HP switcher, the SW600, a few years down the road. Since they were no longer producing cast frame units SW had come to designate Switcher. This “SW” designation held true all the way up to the end of (true) switcher production in the 1970s.
Back in the 1930s, when EMD was known as EMC (Electro-Motive Co.), they were making yard switchers that were powered with the Winton 201 series engines. Winton made 600 and 900 horsepower versions of the 201. ‘S’ stood for 600 hp and ‘N’ stood for 900 hp. The model designations were as follows:
Switchers with a cast frame were either SC or NC
Switchers with a welded frame were either SW or NW
The NW2 was designed in the 1930s, but after the 1000 hp GM 567 engine was introduced the locomotive kept its NW designation. The 600 hp version of the 567 went into the SW1. SW1s and NW2s were produced just before the US entered World War Two and production continued after the war.
The NW2 was replaced by the SW7 in 1949. By this time the ‘S’ and ‘N’ designations were gone and ‘SW’ simply meant ‘switcher’.
!n 1950, the SW8 (800 hp) and SW9 (1200 hp) were introduced. Both used the same carbody except that the SW8 had one exhaust stack and the SW9 had two. The SW1 was still in production during the early 1950s, but by then the notched hood and arched front cab windows were gone.
By 1954, the SW1, SW8, and SW9 were replaced by the SW600 (600 hp), SW900 (900 hp), and SW1200 (1200 hp). The SW600, SW900, and SW1200 all used the same carbody except that the SW600 and SW900 had only one exhaust stack.
The last of the SW series were the SW1000 (1000 hp) and SW1500 (1500 hp), both of which had completely redesigned carbodies with flatter cab roofs and narrower hoods and were introduced in the mid-1960s. Both locos used the newer 645 engine. SW1000s have one stack and SW1500s have two. The SW1001 is basically an SW1000 with a lower profile cab and older style rounded cab roof.
There will be pop quiz on this thread in the near future.
Alas! You appear to have forgotten the SW1504. Admittedly the 60 built only went to Mexico but production was concurrent with EMD’s other 645-powered end-cab switchers of the 1960s and 1970s.