ATSF EMD F units on the San Francisco Chief in 1967.

(Roger Puta, courtesy Marty Bernard, railfan 44, Public domain, via Wikimedia Commons)


GM-EMD logo.


EMD F-units are 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. They were sold to railroads throughout the United States, Canada and 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 (1,000 kW), not "freight". Longer EMD E-units for passenger service had twin 900-horsepower (670 kW) diesel engines (called "prime movers" in that type of application). The E meant "eighteen" as in 1,800 horsepower (1,300 kW). Similarly, for early model EMD switchers, S meant "six hundred" and N meant "nine hundred horsepower" (450 and 670 kW respectively).

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.

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 (main line) diesel locomotives in North America, and were largely responsible for superseding steam locomotives in road freight service. Before that, diesel units were mostly built as switcher locomotives, and only used in rail yards.

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 locomotives on a train included only F-units, the train would then be called a wagon train. Those two usages are still popular with the railfan community.


 Peoria & Western (Keokuk Junction Railway) No. 1752, an EMD FP9 locomotive in yellow and black, at Mapleton, Peoria County, Illinois. Date 8 March 2008. (Nate Beal, CC BY 2.0 <>, via Wikimedia Commons)


SOO No. 2225A, an F7A on Neenah - Argonne Mixed at Gresham, WI in September 1963. (Roger Puta, courtesy Marty Bernard, railfan 44, Public domain, via Wikimedia Commons)

Restored Jersey Central RR EMD F3 unit  No. 56D overnights at Jim Thorpe, PA in May of 1991. (Bruce Fingerhood from Springfield, Oregon, US, CC BY 2.0 <>, via Wikimedia Commons)


Model Designation Year Built Total Produced AAR Wheel Arrangement Prime Mover Power Output
FT 1939–1945 555 A units, 541 B units B-B (B-B+B-B with B unit) EMD 16-567 EMD 16-567A 2,700 hp (2,000 kW) (with B unit)
F2 1946 74 A units, 30 B units B-B EMD 16-567B 1,350 hp (1,000 kW)
F3 1946–1949 1,111 A Units, 696 B-Units B-B EMD 16-567B 1,500 hp (1,100 kW)
F7 1949–1953 2,366 A units, 1,483 B units B-B EMD 16-567B 1,500 hp (1,100 kW)
FP7 1949–1953 381 A units, no B units B-B EMD 567B 1,500 hp (1,200 kW)
F9 1953–1960 99 A units, 156 B units B-B EMD 16-567C 1,750 hp (1,200 kW)
FP9 1954–1959 90 A units, no B units B-B EMD 567C 1,750 hp (1,300 kW)
FL9 1956–1960 60 A units, no B units B-A1A EMD 567C or EMD 567D1;plus 660 V DC(3rd rail) 567C: 1,750 hp(1,300 kW);567D1:1,800 hp(1,340 kW)

Santa Fe EMD FT locomotive which is said to be the world's first successful diesel freight locomotive. (Santa Fe Railway, Public domain, via Wikimedia Commons)

A Rock Island freight train at Joliet, Illinois. The train is led by EMD F2 No. 43,  August 1963. (Lawrence and David Barera, CC BY-SA 2.0 <>, via Wikimedia Commons)

The Amtrak Empire Builder led by BN F3 No. 9762 at Yakima, Washington, in August 1971. (Drew Jacksich, CC BY-SA 2.0 <>, via Wikimedia Commons)

ATSF 309L, an F7A with Train No. 23, The Grand Canyon, in siding at Springer, NM waiting for York Canyon Coal Unit Train, August 19, 1967. (Roger Puta, courtesy Marty Bernard, Roger Puta, Public domain, via Wikimedia Commons)

Model development

The FT, introduced in 1939 with the new 1,350 hp (1.01 MW) 567 engine and Blomberg B trucks, was a successful design, and remained in production during WWII.

The F3 (1946) had a different roof arrangement that included the replacement of the FT's boxy dynamic brake structure with two under-roof grids, two exhaust stacks instead of four, and four cooling fans grouped together instead of separated pairs of cooling fans. The F3 was also 2 feet (0.61 m) longer than the FT to allow a standard draft gear to be installed at the rear of the unit. The 567B engine was uprated to 1,500 hp (1.1 MW). Some F3s were nicknamed "chickenwire" for the type of engine room air-intake structure along the sides.

The F7 (1949) and F9 (1954) were evolutionary: the F7 had improved traction motors, the F9 a 1,750 hp (1.30 MW) 567C engine. A louver arrangement over the vents changed their appearance from the F3.

There were also 4-foot-longer (1.2 m) versions, the FP7 and FP9, the extra length being used to house a tank for extra water capacity. Only one F model did not have Blomberg B trucks: the FL9 electro-diesel locomotive had a lightweight Flexicoil B in front and a standard passenger A-1-A at the rear.

Model descriptions are as built, but EMC/EMD locomotives are often rebuilt to newer standards. 


WP 805A, an EMD FP7 and Train No. 2 at Sparks, NV, 2004. (The original uploader was Evicknair at English Wikipedia., Public domain, via Wikimedia Commons)

Denver and Rio Grande Western F9 A & B units built 1955, retired 1984, at the Colorado Rail Museum in 2009. (Laura Scudder, CC BY-SA 3.0 <>, via Wikimedia Commons)

New Haven FL9 No. 2010 with Train No. 83, a Springfield, Massachusetts to New York City train, near Enfield, CT on July 20, 1968. (Roger Puta, courtesy Marty Bernard, Public domain, via Wikimedia Commons)

Railink (RLGN) 1400, an EMD FP9Au at Waterloo, Ontario, October 7, 2003. (The original uploader was JYolkowski at English Wikipedia., CC BY-SA 3.0 <>, via Wikimedia Commons)

Engine and powertrain

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 mechanically aspirated 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 engine improvement program saw the FT’s original 1,350 hp (1,010 kW) up-rated to 1,800 hp (1,300 kW) in the FL9 by the end of F unit production. A DC generator powered four traction motors, two on each truck. The Blomberg B truck first used in the FT became the EMD production standard, being used until 1995. EMC/EMD built all of its major components after 1939.


Amtrak No. 113, an EMD FP7, leading two EMD SDP40Fs with the San Francisco Zephyr at the Yuba Gap, 1975.

(Drew Jacksich from San Jose, CA, The Republic of California, CC BY 2.0 <>, via Wikimedia Commons)


Passenger service

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 that, EMD offered an optional steam generator on all later F unit models. It 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 and bells.

Dynamic brakes

Dynamic brakes were an option on F units ordered by railroads operating in mountainous terrain and with steep grades.

Passenger or freight pilot

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 fixed and protruded through a rectangular opening in the pilot.