View source for Cow–calf

{{Short description|Pair of switcher locomotives}}
{{Use American English|date=November 2024}}
{{About||the production of beef cattle|cow–calf operation|the rocks in Yorkshire, England|Ilkley Moor}}
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[[File:IC TR1 9251 (big).jpg|thumb|EMD TR1 diesel locomotive with two units—cow and calf]]

In [[rail transport]], a '''cow–calf''' (also '''cow and calf''', or in the {{Abbr|UK|United Kingdom}} '''master and slave''') is a set of [[Diesel locomotive|diesel]] [[switcher locomotive]]s. The set is usually a pair, though a few three-unit sets (with two calves, also known as ''herds'') were built. A cow is equipped with a [[Locomotive cab|cab]], and a calf is not. The two are coupled together (either with regular [[Railway coupling|couplers]] or a semi-permanent drawbar) and equipped with [[multiple-unit train control|multiple unit train control]] so that both locomotives can be operated from the single cab.<ref name="Schafer 1998 p23">{{Cite book |last=Schafer |first=Mike |date=1998 |title=Vintage Diesel Locomotives |location=Osceola, Wisconsin |publisher=Motorbooks International |isbn=0-7603-0507-2 |oclc=38738930 |page=23 }}</ref>

A cow is analogous to an ''[[A unit]]'', i.e. a locomotive with a cab, and a calf to a ''[[B unit]]'', i.e. a powered, cabless [[locomotive|road locomotive]]. That is, the cow and calf are each equipped with at least one [[Prime mover (locomotive)|prime mover]] for propulsion. A cow–calf set is distinct from a ''[[Slug (railroad)|slug]]-and-mother'' set in that a cow and a calf are each independently powered while a ''slug'' has no prime mover and instead is dependent on power from its ''mother'' unit. Like the early [[EMD FT]] locomotives, cow–calf sets were typically built as mated pairs, with the cow and calf sharing a number. However this was not always the case, as over time many of the sets were broken up and couplers added to aid with versatility.

Most cow–calf sets were built by [[Electro-Motive Diesel|Electro-Motive Division]] (EMD), although other examples were built by the [[American Locomotive Company]], [[Baldwin Locomotive Works]], and [[British Rail]] (the last by combining existing locomotives together). Cow–calf sets were made obsolete by the development of [[road switcher]] locomotives, which could handle both mainline trains and switching duties.

==Distinctions between cow–calf, B units, and slugs==
{{Multiple image
| direction = vertical
| image1    = Slug-rebuilt-from-emd-gp8--iowa-interstate-railroad-651--2019-11-09-in-rock-island-illinois.jpg
| image2    = N de M F units led by 6331 of Train 51 (and to be put on 52) at Esperanza, PUE, Mexico on September 11, 1966 (34138482732).jpg
| caption2  = These EMD FP9 locomotives also resemble a cow and calf, but the B unit is designed for mainline speeds, and to be detachable and operate with any other locomotive.
| caption1  = This locomotive and slug of the [[Iowa Interstate Railroad]] resemble a cow–calf set, but the slug has no engines of its own; this allows it to be cut down for better visibility.
}}

Calves are similar to ''[[Slug (railroad)|slugs]]'' (cut-down locomotives which do not have their own engines, but may have control cabs) and especially ''[[B Unit|B units]]'' (powered booster locomotives which do not have cabs).<ref name=":5" /> A calf differs in that a B unit and a slug are both designed to operate with any other locomotives, while a cow–calf set was meant to be semi-permanently coupled to each other and operated together. They were usually connected by drawbars, though some cow–calf sets used standard couplers instead.<ref name=":5">{{Cite web |last=Lustig |first=David |date=April 1, 2011 |title=Difference between a cabless booster, a slug, and a calf |url=https://www.trains.com/trn/train-basics/ask-trains/difference-betwwen-a-cabless-booster-a-slug-and-a-calf/ |website=Trains |access-date=November 12, 2022 }}</ref>

A slug is semi-permanently paired with a cabbed unit, but does not have its own engine. At low speeds, many diesel–electric locomotives can generate more electrical current than can be used by their motors. Slugs use this excess current to power their traction motors. In contrast, all units in a cow–calf set have their own engines.<ref name=":5" />

== History ==

=== Design and nomenclature ===
In a cow–calf set, ''cow'' refers to the locomotive equipped with a cab, while ''calf'' refers to a unit without a cab.<ref name=":3" /> A cow–calf set with two calves is known as a ''herd''; the only examples of this were two [[EMD NW2#TR3 (cow–calf–calf)|TR3]] series sets ordered by the [[Chesapeake and Ohio Railway]].<ref name="Schafer 1998 p23" /><ref name=":1" /> The cow, calf, and herd designations were nicknames.<ref name=":1" />

Cow–calf locomotives were designed both for transferring railroad cars between nearby [[Classification yard|classification yards]] in urban areas and for switching within yards. They were built with an emphasis on tractive effort, with top speed of lesser importance.<ref name="Schafer 1998 p23" />

===Production and operations===
[[File:Belt Railway of Chicago 504 and 512 in Clearing Yard, Chicago, IL in January 1985 (29349135942).jpg|thumb|A [[Belt Railway of Chicago]] cow–calf set in 1985]]

Most cow–calf sets were built between the 1930s and the 1950s. They were built by several different makers, although [[General Motors Corporation|General Motors]]' [[Electro-Motive Diesel|Electro-Motive Division]] built far more than the others, chiefly its TR (transfer) series.<ref name="Schafer 1998 p23" /> In addition to the transfer duties they were designed for, cow–calf sets were also used in [[Classification yard#Hump yard|hump yards]] to send cuts of cars over the hump for classification.<ref name=":4">{{Cite book |last1=Solomon |first1=Brian |url=https://books.google.com/books?id=BOfUBAAAQBAJ&dq=Cow–calf+switcher&pg=PA37 |title=Chicago: America's Railroad Capital: The Illustrated History, 1836 to Today |last2=Blaszak |first2=Michael |last3=Gruber |first3=John |last4=Guss |first4=Chris |date=2014-10-14 |publisher=Voyageur Press |isbn=978-0-7603-4603-7 |page=37 }}</ref>

The [[Union Pacific Railroad]] made use of cow–calf sets as [[Helper locomotive|helpers]] on a steep grade near [[Kelso, California]], until 1959, when the use of [[multiple-unit train control]] made them obsolete.<ref>{{Cite book |url=https://books.google.com/books?id=e--9BRmiycYC&dq=Cow–calf+locomotive&pg=PA111 |title=Kelso Depot Historic Structure Report: Mojave National Preserve, California : an Oasis for Railroaders in the Mojave |date=1998 |publisher=U.S. Department of the Interior, National Park Service |page=111 }}</ref> Most American examples were replaced by [[road switcher]] locomotives.<ref name=":3">{{Cite book |last=Foster |first=Gerald L. |date=1996 |url=https://books.google.com/books?id=ZvSHlCxuyH0C&dq=Cow–calf+switcher&pg=PA10 |title=A Field Guide to Trains of North America |publisher=Houghton Mifflin Harcourt |isbn=978-0-395-70112-6 |page=10 }}</ref> The [[Belt Railway of Chicago]] was the final holdout, continuing to operate TR2 and TR4 sets into the 1980s and 1990s.<ref name=":4" /><ref name=":3" />
<!--Unsourced text commented out for the time being, until/if sources can be found. The cow–calf concept was adopted on [[Two foot gauge railways in Australia|Queensland 2&nbsp;ft gauge]] sugar cane railways with two locomotives being coupled permanently in multiple-unit mode with the cab of one removed. This was utilized by Isis Mill (1980-1993) and by Mackay Sugar (2005). -->

==List of cow–calf models==
[[File:Baltimore and Ohio 9624 (TR4) Cow and Calf at Riverside Yard, Baltimore (22341847029).jpg|thumb|[[EMD TR4]]]]
[[File:Class 13 no. 13003, permanently coupled Master-Slave locomotives, Tinsley Marshalling Yard, Nigel Tout, 6.8.74.jpg|thumb|[[British Rail Class 13]]]]

===TR series===
EMD's TR (transfer) series were the largest group of cow–calf locomotives built. Produced in seven models, eighty were built between 1940 and 1953, along with two additional calves.<ref name="Schafer 1998 p23" /><ref name=":1">{{Cite book |last=Marre |first=Louis A. |url=https://www.worldcat.org/oclc/34531120 |title=Diesel locomotives : the first 50 years : a guide to diesels built before 1972 |date=1995 |publisher=Kalmbach Pub. Co |isbn=0-89024-258-5 |location=Waukesha, Wisconsin |pages=33–36 |oclc=34531120 }}</ref>
* [[EMD TR]]
* [[EMD TR1]]
* [[EMD TR2]]
* [[EMD TR3]]
* [[EMD TR4]]
* [[EMD TR5]]
* [[EMD TR6]]

===Other cow–calf models===
The [[American Locomotive Company]] (ALCO) built two cow–calf sets, derived from the [[ALCO S-6]] and designated ''SSB-9''.<ref name=":2">{{Cite book |last=Wilson |first=Jeff |url=https://books.google.com/books?id=Gt8OtslzijYC&dq=Cow–calf+switcher&pg=PA26 |title=The Model Railroader's Guide to Diesel Locomotives |date=2009 |publisher=Kalmbach Publishing |isbn=978-0-89024-761-7 |pages=22–23, 26–27 }}</ref>

[[Baldwin Locomotive Works]] produced nine cow–calf versions of the [[Baldwin S-8]]. Both ALCO and Baldwin's cow–calf sets all went to customer Oliver Mining.<ref name=":2" />

Cow–calf locomotives in the United Kingdom are generally referred to as ''master and slave'' locomotives. Three sets were created by [[British Rail]] in 1965 by permanently coupling pairs of {{Brc|08}} {{Whyte|0-6-0|DE}} locomotives dating from 1959 and 1962, the cabs and controls being removed from the calves. They were designated ''{{Brc|13}}'' and operated at [[Tinsley Marshalling Yard]], the last being withdrawn in 1985.<ref>{{cite book |last=Marsden |first=Colin J. |date=1981 |title=A Pictorial Record of the Diesel Shunter |publisher=Oxford Publishing Company |location=Oxford |isbn=0-86093-108-0 |pages=108–109 }}</ref><ref>{{cite magazine |last=Marsden |first=Colin J. |date=2018 |title=Locomotive Directory |journal=Modern Locomotives Illustrated |issue=230 |page=43}}</ref> [[British Steel (1967–1999)|British Steel]] created some in a similar manner in 1971 for use at [[Port Talbot Steelworks]]. Four {{Whyte|0-4-0|DE}} locomotives built by [[Brush Traction]] between 1954 and 1957 had their cabs removed and control gear moved into metal cabinets as slaves. Five similar locomotives were equipped to work as masters. The conversions were done in 1971 and they were taken out of service in 1986.<ref>{{cite book |last=Smith |first=Keith |date=1999 |title=Supplement to the West Somerset Railway Stockbook |publisher=West Somerset Railway Association |location=Bishops Lydeard |page=9 |edition=5th }}</ref><ref>{{cite book |title=Industrial Locomotives |date=1982 |isbn=0-901096-44-X |page=232 |edition=6EL |publisher=Industrial Railway Society}}</ref>

==See also==
* [[Slug (railroad)]]
* [[Twin unit]]

==References==
{{Reflist}}

[[Category:Cow–calf locomotives| ]]
[[Category:Diesel locomotives]]