It was produced beginning in 1967 at the request of the Atchison, Topeka and Santa Fe Railway, which did not want its prestigious Super Chief/El Capitan and other passenger trains pulled by freight style hood unit locomotives, which have external walkways.

EMD therefore designed a lightweight "cowl" body to cover the locomotive, though it did not, as in earlier cab units, provide any structural strength, which remained in the frame.

The cowl provided sleeker looks, better aerodynamics at speed, and allowed the crew to enter the engine compartment en route for diagnostics and maintenance.

After a series of derailments and their subsequent withdrawal, Amtrak traded 18 units to the Santa Fe, where they were converted for freight use.

The last three F45s in service were on the Montana Rail Link and the New York, Susquehanna and Western Railway in the northern and northeastern United States.

[citation needed] Between April 1980 and December 1982, Santa Fe's San Bernardino shops rebuilt eight FP45s 5940–5943, 5945–5948.