This locomotive is powered by a sixteen-cylinderEMD 645E3 diesel engine, which could provide 3,000 horsepower (2,240 kW). Illinois Central Railroad used the SD40A as a long-range road-switcher, utilizing the larger fuel tank found on the SDP45.
The Soo Line Railroad eventually acquired five of these units and as of 2005 they are out of service. Six other units (IC 6011, and 6013–6018) remain in service under Illinois Central, which is now a subsidiary of Canadian National Railway