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.

To operate these intercity services the Amtrak had to buy or lease from the private railroads whatever locomotives remained.

Maximum speed at full horsepower was 94 mph (151 km/h);[5] the locomotive exceeded 100 miles per hour (160 km/h) in tests.

Several years earlier, EMD had made similar versions of the SDP45 and SD45 in a full-width cowl unit, which it named FP45 and F45.

EMD wanted to avoid adding a new locomotive type to their catalog due to price controls in effect in the early 1970s.

The most important was the installation of lower-profile cooling fans and air horns to avoid clearance problems in the Eastern US.

The locomotives entered revenue service on June 22, 1973, hauling the Super Chief from Chicago to Los Angeles over the Atchison, Topeka and Santa Fe Railway.

[19] In late 1975 J. David Ingles called the SDP40Fs the "stars of Amtrak's long-distance trains,"[20] but engine crews reported that the locomotives rode poorly compared to the E-units they had replaced.

[21] Even as Amtrak and EMD investigated the ride quality, the SDP40F was involved in a series of derailments that led to the end of its career as a passenger locomotive.

[6] EMD, Amtrak, the Association of American Railroads (AAR), and the FRA tested the locomotive thoroughly, with suspicion falling on the "hollow bolster" truck design.

In the end, the investigators theorized that the steam generators and water tank may have made the rear of the engine too heavy and created too much lateral motion.

[4] Later FRA investigations concluded that the actual culprit was the light weight of the baggage cars, which caused harmonic vibrations when placed directly behind the much heavier SDP40F.

[26] Another important development was the unusually harsh winter of 1976–1977, which sidelined many of Amtrak's aging steam-heated coaches.

Amtrak suspended numerous routes and pressed the new HEP-equipped Amfleet I coaches, designed for short runs, into service.

[28] Amtrak decided to abandon the SDP40F in favor of the F40PH, a four-axle design with none of the riding problems of the six-axle locomotives.

The SDP40F remained in service on the Santa Fe longer than elsewhere, although the arrival of HEP-equipped Superliner cars on the Western routes displaced them from there as well.

644 (later ATSF 6976), was acquired by Dynamic Rail Preservation Inc. and is in Boulder City, Nevada having been previously displayed in Ogden, Utah.