As an alternative to the reconstruction measures of older road switcher locomotives, EMD has been offering the GP15-1 since 1976. It was a short four-axle vehicle with a 1,500 hp twelve-cylinder prime mover that did not have a turbocharger. These locomotives could be used inexpensively for light road or switching service and a total of 310 were built by 1982. Of these, 160 went to the Missouri Pacific Railroad, which was bought by the Union Pacific shortly thereafter. Another 100 went to Conrail and 25 each to the Chicago and North Western and the St. Louis-San Francisco Railway.

After the end of production, the GP15T was presented, which was identical in dimensions and power to the GP15-1. The difference was that the prime mover used was a smaller turbocharged eight-cylinder. Due to the same power with a smaller displacement and a lower number of cylinders, this engine could be used more economically. Chessie System with 25 engines and Apalachicola Northern with three more were found as buyers. As the lower maintenance costs and higher reliability of a non-turbocharged engine were more important to many operators at the time, no further GP15Ts were built.