The EMD SDP40F was a six-axle 3,000 hp (2.2 MW) C-Cdiesel–electriclocomotive built by General Motors Electro-Motive Division (EMD) from 1973 to 1974. Based on Santa Fe's EMD FP45, EMD built 150 for Amtrak, the operator of most intercity passenger trains in the United States. Amtrak, a private company but funded by the United States government, had begun operation in 1971 with a fleet of aging diesel locomotives inherited from various private railroads. The SDP40F was the first diesel locomotive built new for Amtrak and for a brief time they formed the backbone of the company's long-distance fleet.
A series of derailments in the mid-1970s shattered Amtrak's confidence in the locomotive, and many railroads banned it from their tracks. Multiple investigations pointed to issues with the locomotive's trucks, the weight of the water and steam generators used for train heating, the rough and poorly maintained tracks, or the harmonic vibration of baggage cars behind the locomotive. In 1977, Amtrak decided to retire the SDP40F in favor of the EMD F40PH, which was already in use on short-distance routes. Amtrak traded most of its fleet into EMD; the components were incorporated into new F40PHs. The remainder were traded to the Atchison, Topeka and Santa Fe Railway (ATSF) for use in freight service. The Santa Fe rebuilt the locomotives and designated them SDF40-2. The Burlington Northern Santa Fe Railway (BNSF), successor to the Santa Fe, retired them in 2002. One of them is preserved, that one being ex-Amtrak No. 644.
