 EMD was initially hesitant to turbocharge their 567-series diesel engine, but was spurred on to do so following successful tests made by Union Pacific in the form of UP's experimental "Omaha GP20" units.260 examples of EMD's production locomotive model (with the EMD turbocharger) were built for American railroads.The GP20 was the second EMD production locomotive to be built with an EMD turbocharged diesel engine, sixteen months after the six-axle (C-C) model SD24.