F unit

EMD F-units were a line of diesel-electric locomotives produced between November 1939 and November 1960 by General Motors Electro-Motive Division and General Motors-Diesel Division. Final assembly for all F-units was at the GM-EMD plant at La Grange, Illinois and the GMDD plant in London, Ontario, Canada. They were sold to railroads throughout the United States, Canada, Mexico and a few were exported to Saudi Arabia. The term F-unit refers to the model numbers given to each successive type (i.e. F3, F7, etc.), all of which began with the letter F. The "F" originally meant Fourteen, as in 1,400 horsepower, not F as in Freight. Longer E-units for passenger service had twin 900 horsepower diesel engines (called "prime movers" in this type of application). The "E" meant Eighteen as in 1,800 horsepower. Similarly, for early model EMD switchers "S" meant Six hundred and "N" meant Nine hundred horsepower.

F-units were originally designed for freight service – although many without steam generators (for steam-heating passenger cars) pulled short-distance, mainly daytime passenger trains. Some carriers even equipped small numbers of their Fs with steam generators for long-haul passenger service. On the other hand, Santa Fe maintained a large fleet of fully equipped, high-speed F3s and F7s in "warbonnet" paint schemes built exclusively for top-tier passenger trains such as the "Chief", "Super Chief", and "El Capitan". 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 in F-units was a sixteen-cylinder EMD 567 series mechanically aspirated two-stroke diesel engine, progressing from model 16-567 through 16-567D.

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