Rivet Counter HO Scale EMD SD7, Burlington Northern/White Stripes on Both Hood Ends/Mars Dual Signal Lights

In the peacetime immediately following World War II, EMD was poised to take the lead in diesel-electric locomotive technology, with America’s railroads eager to replace steam and enjoy the performance and efficiency gains from doing so. Their groundbreaking FT, and subsequent F and E series locomotives were immensely popular, and by the early 1950s, they could be seen hauling freight and passenger trains from coast to coast.

As popular as they were, however, the basic design of these cab units had a fundamental operational flaw: poor rearward visibility. While their streamlined design was fine for moving passenger or freight trains long distances, when it came time for switching, the design was less than ideal, making it difficult for engineers to see crew members on the ground, not to mention poor visibility when making reverse movements, which happened often when doing yard work or running local freights on branch lines. EMD's solution was the BL1 (“BL” standing for “Branch Line”) locomotive of 1948, and the subsequent BL2. Essentially a re-packaged F-unit, they retained the truss body framing of the F-unit series, with the sheet metal around it re-designed in an attempt to provide improved visibility in either direction, and provide corner steps and grabs for switchmen. 

While an interesting concept, they were not well-received by the railroads, with only a single BL1 and a total of 58 BL2s built. In 1949, EMD would try again with a clean-sheet utilitarian design that was to prove wildly successful: the GP7. With the “GP” designation standing for “General Purpose”, in a nod to its jack-of-all-trades versatility, it was essentially an F7 internally, with a 16-567B prime mover generating 1,500hp, and riding on a pair of the proven “Blomberg” 2-axle trucks. Its key design feature was an all-new fabricated frame, replacing the truss structure of the F/E units. This allowed for a narrow hood to house the internal machinery, side walkways and end platforms, and much deeper steps at the corners for switchmen. All of this made for a locomotive with much greater visibility in either operating direction and easier access to the internal components for maintenance.  

Building on the success of the GP7, in 1951, EMD would take the General Purpose concept a step further with the introduction of the SD7, with “SD” indicating “Special Duty”. While internally it was basically an F7 or GP7, externally it featured a lengthened frame with a pair of 3-axle “Flex-i-Coil” trucks, with a traction motor per axle. While the 4-axle GP7 was fine in most applications, its 4-axles and traction motors could be a bit “slippery” in others, such as hilly/mountainous territory, and on high-tonnage coal or ore trains. The additional pair of axles and traction motors of the SD7 provided greater tractive effort to help start heavy trains and keep them moving on all kinds of territory, as well as helping to distribute the weight of the locomotive, allowing them to operate on lines with lighter rail and/or less-than-ideal trackwork.

Purchased by numerous railroads, the SD7 was a success, with a total of 188 built. Versatile, when equipped with optional steam generator equipment housed in the high short hood, it could be used for passenger service, and was utilized as such on roads like the Burlington Route and Southern Pacific. Another distinctive feature of the SD7 was its fuel and/or water tanks. It could be optioned with a single 1,200-gallon fuel tank, leaving a large gap between it and the front truck, a dual tank setup for passenger service, which had an additional 1,200-gallon tank for steam generator water installed ahead of the fuel tank, or a pair of 1,200-gallon tanks for fuel. In later years, some railroads with the split fuel and water tank arrangement would convert the water tank for fuel only when their passenger hauling days were done, and roads with light trackwork could opt for just a single fuel tank to help keep overall locomotive weight down.

Coinciding with EMD's changeover to the E/F9 series and GP9, the SD7 would morph into an improved model, the SD9, in 1954. Internally, horsepower got a boost to 1,750, while externally, not much changed from the SD7, at least on initial production. The class light placement was the one readily noticeable difference between the two; while the SD7 featured class lights built into hinged doors placed close to the centerline on each end, on the SD9, they were located at the upper corners of the hood ends, in a fixed mounting. While the SD7 had a pair of inset steps at the corners, the SD9 would have a revised corner step arrangement, with full-depth steps at all locations. With a total of 471 units built for domestic owners, over an extended period of time, the SD9 would undergo cosmetic changes over that timeframe, resulting in what railfans and modelers call production “phases”. Aside from the class lights, early SD9s weren’t much different from SD7s, but this would change with what were dubbed “Phase II '' units, introduced in early 1955. EMD would change the multi-piece “pipe” handrail stanchions from SD7s and early SD9 production, to “channel” style stamped handrail stanchions to help reduce production costs, a design that was to become standard on nearly all subsequent EMD production.

Another phase change, “Phase III”, would be introduced in early 1958. This time, EMD would revise the cooling system, changing from four 36” radiator fans at the rear of the long hood roof to a pair of 48” fans. Finally, “Phase IV” units, introduced in early 1959, would round out SD9 production with a slew of physical changes. Up front, the cab sub-base would increase in height, and the battery boxes, previously located on the walkways behind the cab, would be relocated to the walkways immediately ahead of the cab. The taller battery boxes and cab sub-base resulted in the cab and high short hood sitting taller than previous production, resulting in a bit of a “hammerhead” appearance. The long hood immediately behind the cab also featured a change in its profile, losing its rounded corners and changing to a more squared-off corner profile. 

The SD7 and successor SD9 locomotives would prove to be popular and long-lived machines. Most major railroads of the era would purchase examples of SD7s and/or SD9s, using them in a multitude of assignments. With such a variety of owners, many differences in optional equipment could be seen, ranging from just standard headlights to extensive lighting packages, to steam generator equipment, to fuel/water tank combinations, and on and on, resulting in many unique-looking SD7s and SD9s. The models would eventually acquire the nickname “Cadillac” among their operators. Much like the GM automobile line of the same name, they were powerful and offered a smooth ride, which was much appreciated by engineers and conductors who endured bone-jarring rides in locomotives from competitors.

By the 1970s, many of these rugged SDs were due for rebuilding, and many railroads would do just that, in order to improve their reliability, maintainability, and lengthen their service lives. While some rebuilds were mostly focused on renewing or updating internal components, some railroads would implement more extensive changes, such as lowering the high short hoods all were initially built with, to a low short hood arrangement with cab face center windshields, to improve forward visibility. While most would be retired by the 90s and sold to secondary operators, a few fleets would linger on for their original (or successor) owners, such as BNSF, Southern Pacific, and Norfolk Southern. By the early 2000s, the last of these long-lived units would be purged from Class One rosters, but many “Cadillacs” are still out there. While they may be in less demanding roles at grain elevators or shortline railroads, they’re still moving freight after upwards of over seven decades of service.