EMD GP38AC

The EMD GP38AC was a diesel-electric road switcher produced by General Motors Electro-Motive Division between February 1970 and December 1971. A total of 261 units were constructed during this relatively brief production window, making it a moderately successful variant within EMD's expanding GP38 family. The locomotive was purchased by a diverse range of North American railroads, including the Canadian Pacific, Detroit, Toledo and Ironton, Grand Trunk Western, Gulf, Mobile and Ohio, Illinois Central, Lehigh Valley, Louisville and Nashville, Norfolk and Western, St. Louis-San Francisco (Frisco), Southern Railway, and Pacific Power and Light. The GP38AC occupied a specific niche in EMD's catalog by offering customers the flexibility of alternating current power generation while retaining the familiar 2,000 horsepower rating and overall platform of the standard GP38. As the Dash 2 era arrived in the early 1970s, many GP38AC units were subsequently upgraded to full GP38-2 specification through the installation of the modular electrical cabinets that defined that later series. This upgrading program helped extend the working lives of numerous units well beyond what might otherwise have been expected, blurring the line between the two generations on some rosters. At least one example has been preserved for public display. BNSF 2127, which was originally constructed in February 1971 as Frisco number 650, was donated in June 2020 to the Galveston Railroad Museum in Galveston, Texas, ensuring that a representative of this relatively short-lived model survives for future generations.

The GP38AC was mechanically and structurally identical to the standard GP38 in most respects, riding on a B-B wheel arrangement with four powered axles driving the locomotive through DC traction motors. Power came from EMD's 645E prime mover, a 16-cylinder two-stroke diesel engine producing 2,000 horsepower. The defining characteristic that distinguished the GP38AC from its GP38 counterpart was the substitution of an AR10 alternator in place of the direct current generator found in the base model. This alternating current generating equipment fed rectified power to the traction motors, representing an intermediate step in EMD's broader industry transition toward fully integrated alternator-based electrical systems that would be standardized in the Dash 2 line. The use of the AR10 alternator was considered advantageous by some operators for its reliability and output characteristics relative to conventional DC generators, though the GP38AC still employed DC traction motors rather than the fully AC-drive systems that would come to dominate the industry decades later. The locomotive's 2,000 horsepower output placed it in the middle tier of EMD's road switcher offerings of the period, making it well suited for branch line service, local freight assignments, and helper duty on lines that did not require the higher horsepower of the GP40 or SD45 series.