Amtrak SDP40F units 513 and 504, in their first year of service, pause at Fort Worth depot with the Texas Chief in March 1974. Electro-Motive's SDP40-F was the first new locomotive ordered by Amtrak, which acquired 150 units in 1973-1974. The design was based on the SD40-2 freight locomotive but had a wider carbody, passenger gearing allowing a maximum speed of 100 m.p.h., two steam generators, and a 5000-gallon water tank for use with legacy passenger equipment.
The SDP40F experienced several derailments at high speed, as a result of which restrictions were imposed on its operation. Although poor track conditions in the 1970s on the host railroads may have contributed to these derailments, the exact cause was never determined. One theory is that the extra weight of the steam generating equipment unbalanced the weight distribution to the point that the lead truck tended to lift off the rails. Eventually the SDP40-F was phased out after new passenger equipment, heated by head-end power from newer diesel models, was placed in service. A few were sold to other railroads and converted to freight locomotives.