Editing EMD F-unit (section)

{{Short description|Line of diesel-electric locomotives}}
{{More footnotes needed|date=August 2013}}
[[File:ATSF 21L F3A with Train -2, the San Francisco Chief between Willow Springs, IL and Lemont, IL on the only stretch of ATSF track in DuPage County on January 2, 1967 (22692932325).jpg|300px|thumb|[[Atchison, Topeka and Santa Fe Railway|AT&SF]] {{abbr|No.|Number}}&nbsp;21, an EMD F3, leading the ''[[San Francisco Chief]]'' in Illinois in 1967]]
'''EMD F-units''' are a line of [[diesel-electric locomotive]]s produced between November 1939 and November 1960 by [[General Motors Corporation|General Motors]] [[Electro-Motive Diesel|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 [[railroad]]s 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 {{convert|1400|hp}}, not "freight". Longer [[EMD E-units]] for passenger service had twin {{convert|900|hp|adj=on}} diesel engines (called "[[Prime mover (locomotive)|prime movers]]" in that type of application). The ''E'' meant "eighteen" as in {{convert|1800|hp}}. Similarly, for early model EMD switchers, ''S'' meant "six hundred" and ''N'' meant "nine hundred horsepower" ({{cvt|600|and|900|hp|disp=out}} respectively).{{citation needed|date=February 2021}}
<!-- Image with inadequate rationale removed: [[Image:EMD FT demonstrator.jpg|thumb|250px|EMD's FT demonstrator set No.&nbsp;103, the locomotive that sold US railroads on the freight-hauling Diesel-electric locomotive.]] -->

F-units were originally designed for freight service, although many without [[Steam generator (railroad)|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, [[Atchison, Topeka and Santa Fe Railway|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 (train)|Chief]]'', ''[[Super Chief]]'', and ''[[El Capitan (train)|El Capitan]]''. Almost all F-units were [[AAR wheel arrangement#B-B|B-B]] locomotives, meaning that they ran on two [[Blomberg B]] two-axle [[bogie|trucks]] with all axles powered. The prime mover in F-units was a sixteen-cylinder [[EMD 567|EMD 567 series]] [[roots type supercharger|mechanically aspirated]] [[Two-stroke engine#Two-stroke diesel engine|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 locomotive]]s in road freight service. Before that, diesel units were mostly built as [[switcher locomotive]]s and only used in rail yards.

F-units were sometimes known as "covered wagons",<ref>See, e. g., Young, William S. "Covered Wagons: The Early Road Diesels of the Erie Lackawanna" (1976, Starrucca Valley Publications).</ref> 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.