EMD GP15AC

The EMD GP15AC was a specialized variant of the GP15 family of road switchers, produced by General Motors Electro-Motive Division during a brief production window in November and December of 1982. The locomotive emerged during a period when railroads were weighing the costs of rebuilding aging first-generation motive power against acquiring newer, purpose-built alternatives. EMD designed the GP15 series to occupy a middle ground, offering modern construction with modest horsepower suitable for yard work and light road assignments. The GP15AC represented a specific refinement of that concept, tailored to the preferences of its primary customer, the Missouri Pacific Railroad. Missouri Pacific was by far the dominant purchaser of the GP15AC, acquiring 30 units as part of its broader strategy of maintaining a flexible and economical locomotive fleet for branch line and terminal operations. An additional four units were delivered to IFE, the Venezuelan railway operator, bringing the total production run to 34 locomotives. This relatively small production figure stands in contrast to the GP15-1, which found considerably broader market acceptance across multiple American railroads, but the GP15AC nonetheless represented a meaningful expression of customer-driven specification within the GP15 program. Missouri Pacific's units eventually passed into the Union Pacific fleet following the 1982 merger of those two railroads, where they continued to perform light-duty service. The GP15AC occupies a modest but distinct place in the history of EMD's product line as one of the few examples of a production locomotive in this power category specified with an AC alternator rather than a DC generator. Though built in limited numbers and never widely replicated, the variant demonstrated the degree to which major customers could influence the configuration of even a standardized locomotive design. The broader GP15 family, of which the GP15AC was a part, proved durable enough that many examples remained in service for decades, and Union Pacific undertook rebuild programs on related GP15-1 units to extend their operational lives further.

The GP15AC was powered by a naturally aspirated, 12-cylinder EMD 645E prime mover producing 1,500 horsepower, the same engine configuration used in the GP15-1. The defining characteristic that set the GP15AC apart from its GP15-1 sibling was the substitution of an AR10 AC alternator in place of the rebuilt D32 DC generator used in the standard variant. Despite this electrical difference, the locomotive still drove conventional DC traction motors, meaning the alternator's output was rectified before reaching the running gear. The locomotive rode on a B-B wheel arrangement using Blomberg-style trucks, consistent with others in the GP15 family. Our database notes the model as a rebuilt type incorporating GP7 and GP9 components, suggesting the carbody or certain mechanical elements drew on remanufactured parts from earlier first-generation EMD road switchers rather than being entirely new construction. Externally, the GP15AC was difficult to distinguish from the GP15-1 at a glance, with the primary visual difference being a straight side sill profile, a feature shared with the GP15T variant and unrelated to the internal transmission differences. The locomotive's radiator section bore a resemblance to those found on the tunnel motor variants of the SD40 and SD45 families, a design choice that occasionally led observers to misidentify the units. This characteristic earned GP15 family members the informal nickname of baby tunnel motors among railroad enthusiasts. The 10-unit figure recorded in some sources for the GP15AC likely reflects a subset or partial order rather than the full production total of 34 units documented across all customers.

Models by: Athearn