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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, all of which began with 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. The E meant Eighteen as in 1,800 horsepower. Similarly, for early EMD locomotives S means Six hundred and N means Nine hundred horsepower.
F-units were originally designed for freight service, although many hauled passenger trains. Almost all F-units were B-B locomotives; 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.
Structurally, the locomotive was a carbody unit, with the body as the main load-bearing structure, designed like a bridge truss and covered with cosmetic panels. The so-called bulldog nose was a distinguishing feature of the locomotive's appearance, and made a lasting impression in the mind of the traveling public.
The F-units were the most successful "first generation" road Diesel locomotives in North America, and were largely responsible for superseding steam locomotives in road freight service.
F-units were sometimes known as covered wagons, due to the similarity in appearance of the roof of an F-unit to the canvas roof of a Conestoga wagon, an animal-drawn wagon used in the westward expansion of the United States during the late 18th and 19th centuries. When a train's locomotive consist included only F-units, the train would then be called a wagon train. These two usages are still popular with the railfan community.
|Model designation||Build year||Total produced||AAR wheel arrangement||Prime mover||Power output||Image|
|FT||1939–1945||555 A units,|
541 B units
(B-B+B-B with B unit)
(with B unit)
|F2||1946||74 A units,|
30 B units
|B-B||EMD 16-567B||1,350 hp|
|F3||1946–1949||1,111 A units,|
696 B units
|B-B||EMD 16-567B||1,500 hp|
|F7||1949–1953||2,366 A units,|
1,483 B units
|B-B||EMD 16-567B||1,500 hp|
|FP7||1949–1953||381 A units||B-B||EMD 567B||1,500 hp|
|F9||1953–1960||99 A units,|
156 B units
|B-B||EMD 16-567C||1,750 hp|
|FP9||1954–1959||90 A units,|
no B units
|B-B||EMD 567C||1,750 hp|
|FL9||1956–1960||60||B-A1A||EMD 567C or|
plus 660V DC
The F3 (1946) had a different roof arrangement, and slightly different dimensions, than the FT. The 567B engine was uprated to 1,500 hp (1.1 MW). F3s were often nicknamed “chickenwire” for the vents along the top of the sides.
There were also 4 foot longer versions, the FP7 and FP9, with room for increased passenger train heating. Only one F model did not have Bloomberg B trucks, the FL9 had a lightweight Flexicoil B in front and a standard passenger A-1-A at the rear.
The F series used a 16 cylinder version of the 567 series diesel engine, introduced in 1939. The 567 was designed specifically for railroad locomotives, a supercharged 2 stroke 45 degree V type with 567 cu in (9.29 L) displacement per cylinder, for a total of 9,072 cu in (148.66 L). An ongoing improvement program saw the FT’s 1,350 hp (1.01 MW) up-rated to 1,800 hp (1.3 MW) in the FL9. A D.C. generator powered four traction motors, two on each truck. The Blomberg B truck first used in the FT became the EMD standard, being used through 1995. EMC/EMD has built all of its major components since 1939 
While the F-unit series was originally conceived for freight service, many were used to haul passenger trains. The original EMC FT demonstrator was equipped with a steam generator in the B units for train heating. Several railroads took advantage of the large space in the rear of their B units to add steam generators. The first FTs built strictly as a passenger unit was the Santa Fe 167 four unit set in February 1945. Learning from this, EMD offered an optional steam generator on all later F unit models. This was mounted at the rear of the carbody; steam-generator equipped locomotives can be recognised by the exhaust stack and safety valves protruding at the rear of the roof.
The F units were popular passenger locomotives on mountain grades (where they were recommended by EMD), because a four-unit set had more motored axles than a trio of E-units of equivalent power (sixteen versus twelve) and thus had less chance of overloading the traction motors. Additionally, that 4-unit F set had all its weight on driven wheels and was thereby capable of greater tractive effort. The AT&SF Super Chief, CB&Q/D&RGW/WP California Zephyr, and GN Empire Builder all used F units on their Chicago-West Coast routes in the 1950s. The F7 was also popular for commuter lines and other passenger service where the trains were short.
There were several options that could be specified by customers, such as type and mounting location of horns, bells, and the like.
Dynamic brakes were an option on F units ordered by railroads with mountainous terrain and steep grades.
Either a passenger or freight style pilot could be ordered. The passenger pilot, similar to that standard on EMD E units, sloped smoothly down from the bottom of the nose, making a single slope all the way down from the headlight. The coupler was retractable with concealing doors. The result was a very attractive appearance that enhanced the impression of a powerful and speedy machine.
The freight pilot curved inward a little way below the bottom of the nose before sloping out again, to give more clearance to the coupler and hoses. The coupler was non-retractable and protruded through a rectangular opening in the pilot.