For those who model the steam-diesel transition era, as I do, the chronology of locomotive introduction is important if era accuracy is a goal. Of course many choose to model an “elastic” era, in order to include whatever their favorite aspects of the SP may be, even though they are not strictly contemporaneous. That’s okay, but it’s not what I’m trying to do.
I published an article with a diesel road locomotive timeline for the SP, covering 1947 to 1956. It was in the SP Historical & Technical Society magazine, Trainline, issue no. 29 (I think 1992). I constructed this timeline partly for my own use in modeling. I don’t want to repeat that article here, but will mention some relevant parts as I work on needed locomotives for my layout.
The SP’s mainstay road diesels were the EMD F3 and F7 units, delivered from June of 1947 onward, and continuing into 1953. During 1953, SP management obviously changed preferences in favor of hood unit power, and SD7 as well as Alco RSD-5 locomotives were purchased to work alongside the Baldwin road-switchers already on the railroad.
This is important because it was not until 1954 that the first SD9 and GP9 locomotives arrived. Personally, I love the looks of both of these EMD classics, especially in “Black Widow” paint, but they unfortunately are just too late to use on a 1953 layout. I own nice models of both the SD9 and GP9 engines and may occasionally run them to enjoy their looks, but properly they do not belong on my layout when it’s being operated seriously.
I know some readers will say, "what difference can it make? Run what you want,” doubtless adding the old saw, “after all, it’s your railroad.” But everyone has to draw a line somewhere. Would you suggest I then compromise and operate the distinctive Alco RS-11 engines, very handsome also but which didn’t arrive until late 1956? Why not a few red/gray locomotives among all the Black Widow engines? Heck, why not SP’s signature SD45 or tunnel motor power, if you like them?
Well, that’s not my approach to modeling. I choose to draw my line at the end of 1953. The same thinking applies to the recent very nice HO models of 1954-model Ford trucks. Too bad, they just won’t fit if I’m sticking to 1953. If I wish to be consistent with freight car paint and lettering to reflect 1953 (and I do), I believe it’s equally important for highway vehicles and, yes, diesel locomotives to exhibit the same consistency.
It happens that there is extensive photographic evidence for all the 1953-era diesels mentioned above being used on the Coast Line, though the RSD-5 engines only had a brief tryout and most SD7 engines worked on the NWP in 1953. So F3, F7, and Baldwin power should be the mainstay of my lineup of 1953 Coast Line road diesels.
All this is part of an important modeling goal for me: creation of a model scene and model operations that consistently reflect a specific era. As I’ve mentioned in prior posts, to me this is more important than recreating a specific place. Diesel locomotive chronology is just part of that effort.