EMD SD45

The EMD SD45 entered production in 1965 as one of the most powerful single-unit diesel-electric locomotives available on the American market at the time. Built by General Motors' Electro-Motive Division, the SD45 was aimed at railroads seeking maximum horsepower in a single unit to handle heavy freight over demanding grades. Over the course of its production run, which extended through 1971, EMD delivered a total of 1,260 units to numerous Class I railroads across the United States. Buyers included some of the largest and most demanding freight carriers of the era, among them the Southern Pacific, Burlington Northern, Santa Fe, Pennsylvania Railroad, Great Northern, Union Pacific, Denver and Rio Grande Western, Southern Railway, Norfolk and Western, and Northern Pacific. Despite its impressive power output, the SD45 developed a reputation for reliability problems stemming from its twenty-cylinder prime mover. The large engine was prone to crankshaft failures caused by flexing of the engine block, a problem that required EMD to reinforce the block design partway through the locomotive's production life. Some railroads concluded that the extra 600 horsepower the SD45 offered over the sixteen-cylinder SD40 did not justify the added maintenance burden, particularly since at low speeds, where tractive effort was constrained by wheel-to-rail adhesion rather than raw power, the two locomotives performed comparably. These concerns gradually shifted railroad purchasing preferences toward the SD40 and ultimately toward the more refined SD40-2 introduced in 1972. The SD45 was succeeded in the EMD catalog by the SD45-2, which incorporated the Dash-2 modular electrical system, but the type never regained the commercial momentum it had briefly enjoyed. The SD45's legacy extended well beyond its original service lives. Southern Pacific undertook an extensive rebuild program at its Sacramento Shops, converting 167 units into the SD45R configuration under its M-99 program. The Atchison, Topeka and Santa Fe rebuilt 115 examples into the SD45u variant between 1979 and 1989. A number of units were re-engined with sixteen-cylinder 645 prime movers and downrated to approximately 3,000 horsepower, effectively converting them to SD40-2 equivalents. Montana Rail Link operated a fleet that retained the original twenty-cylinder engines into the 21st century, making that railroad a notable holdout for the type in something close to its original configuration. Several examples have been preserved at railroad museums across the country, including the first production unit, Great Northern 400, known as "Hustle Muscle," which is maintained by the Great Northern Railway Historical Society.

The SD45 was built on a C-C wheel arrangement, meaning it rode on two three-axle trucks, giving it six powered axles in total. Its prime mover was the EMD 645E3, a twenty-cylinder version of the 645 series two-stroke diesel engine that produced 3,600 horsepower. This made the SD45 the highest-horsepower locomotive in the standard EMD catalog during the mid-1960s, sharing its carbody platform with the SD38, SD39, SD40, and SDP40 but distinguished by the longer hood necessary to accommodate the larger engine. Traction was transmitted through a conventional DC electrical system, with the diesel engine driving a main generator that supplied current to six traction motors, one per axle. The locomotive's overall length and weight distribution were calibrated for heavy road freight service rather than yard switching, and its six-axle configuration provided the adhesion necessary to move long tonnage trains. EMD also produced a small experimental variant designated the SD45X, of which seven units were constructed. Six of these went to Southern Pacific and one was retained by EMD for testing purposes. The SD45X featured a more powerful version of the 645E3 engine reportedly capable of producing up to 4,200 horsepower, along with revised truck designs intended to improve adhesion and modified radiator fan arrangements visible at the long hood end. The SD45X was intended to serve as a development platform pointing toward a proposed next generation of EMD power, but that program did not advance to full production, and the seven experimental units remained unique examples of a path not taken in EMD's development history.

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