N EMD F7A Locomotive - Western Maryland - Circus
F-units were a line of diesel-electric locomotives produced between November 1939 and November 1960 by Electro-Motive Division of General Motors and General Motors-Diesel Division. Final assembly for all F-units was done at the GM-EMD plant in La Grange, Illinois and the GMDD plant in London, Ontario, Canada. They were sold to railroads throughout the United States, Canada, and Mexico.
The first production F-unit, the iconic FT, has been dubbed "the diesel that did it" because as the first universally successful freight unit, the model was largely responsible for the beginning of replacing steam power with diesels.
F-units were originally designed for freight service. Additionally, many without steam heating equipment necessary to steam-heat passenger cars, pulled short-distance, mainly daytime passenger trains. Many carriers equipped their F-units with steam generators for long-haul passenger service including Santa Fe, Great Northern, Northern Pacific, Canadian Pacific, and Canadian National among others. Almost all F-units were B-B locomotives, meaning that they ran on two Blomberg B two-axle trucks with all axles powered. The prime mover used in F-units was a sixteen-cylinder EMD 567 series two-stroke diesel engine progressing from model 16-567 through 16-567D as improvements were made.
Model designations began with the FT, moving to the F3, F7, and the F9. Locomotives built specifically for passenger service were longer than the freight version and carried a "P" designation such as FP7 and FP9.
Widespread use of F-units on Class 1 railroads ended in the late 1970's as larger, more powerful locomotives took over. While seldom seen in freight service anymore, several shortlines, tourist operations, and Class 1 railroads continue to use F-units in passenger hauling duties to this day.