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rail transport Rail transport (also known as train transport) is a means of transport using wheeled vehicles running in railway track, tracks, which usually consist of two parallel steel railway track, rails. Rail transport is one of the two primary means of ...
, a cow–calf (also cow and calf, or in the master and slave) is a set of diesel switcher locomotives. 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 cab, and a calf is not. The two are coupled together (either with regular couplers or a semi-permanent drawbar) and equipped with multiple unit train control so that both locomotives can be operated from the single cab. A cow is analogous to an ''
A unit An A-unit, in railroad terminology, is a diesel locomotive (or more rarely an electric locomotive) equipped with a driving cab and a control system to control other locomotives in a multiple unit, and therefore able to be the lead unit in a c ...
'', i.e. a locomotive with a cab, and a calf to a '' B unit'', i.e. a powered, cabless road locomotive. That is, the cow and calf are each equipped with at least one prime mover for propulsion. A cow–calf set is distinct from a ''
slug Slug, or land slug, is a common name for any apparently shell-less Terrestrial mollusc, terrestrial gastropod mollusc. The word ''slug'' is also often used as part of the common name of any gastropod mollusc that has no shell, a very reduced ...
-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 Division Electro-Motive Diesel (abbreviated EMD) is a brand of diesel-electric locomotives, locomotive products and diesel engines for the rail industry. Formerly a division of General Motors, EMD has been owned by Progress Rail since 2010. Electro-Motiv ...
(EMD), although other examples were built by the
American Locomotive Company The American Locomotive Company (often shortened to ALCO, ALCo or Alco) was an American manufacturer that operated from 1901 to 1969, initially specializing in the production of locomotives but later diversifying and fabricating at various time ...
,
Baldwin Locomotive Works The Baldwin Locomotive Works (BLW) was an American manufacturer of railway locomotives from 1825 to 1951. Originally located in Philadelphia, Pennsylvania, it moved to nearby Eddystone, Pennsylvania, Eddystone in the early 20th century. The com ...
, and
British Rail British Railways (BR), which from 1965 traded as British Rail, was a state-owned company that operated most rail transport in Great Britain from 1948 to 1997. Originally a trading brand of the Railway Executive of the British Transport Comm ...
(the last by combining existing locomotives together). Cow–calf sets were made obsolete by the development of
road switcher A road switcher locomotive is a type of railroad locomotive designed to both haul railroad car, railcars in mainline service and Shunting (rail), shunt them in railroad yards. Both type and term are North American in origin, although similar t ...
locomotives, which could handle both mainline trains and switching duties.


Distinctions between cow–calf, B units, and slugs

Calves are similar to ''
slugs Slug, or land slug, is a common name for any apparently shell-less terrestrial gastropod mollusc. The word ''slug'' is also often used as part of the common name of any gastropod mollusc that has no shell, a very reduced shell, or only a sma ...
'' (cut-down locomotives which do not have their own engines, but may have control cabs) and especially '' B units'' (powered booster locomotives which do not have cabs). 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. 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.


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. A cow–calf set with two calves is known as a ''herd''; the only examples of this were two TR3 series sets ordered by the
Chesapeake and Ohio Railway The Chesapeake and Ohio Railway was a Class I railroad formed in 1869 in Virginia from several smaller Virginia railroads begun in the 19th century. Led by industrialist Collis Potter Huntington, it reached from Virginia's capital city of Rich ...
. The cow, calf, and herd designations were nicknames. Cow–calf locomotives were designed both for transferring railroad cars between nearby 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.


Production and operations

Most cow–calf sets were built between the 1930s and the 1950s. They were built by several different makers, although
General Motors General Motors Company (GM) is an American Multinational corporation, multinational Automotive industry, automotive manufacturing company headquartered in Detroit, Michigan, United States. The company is most known for owning and manufacturing f ...
'
Electro-Motive Division Electro-Motive Diesel (abbreviated EMD) is a brand of diesel-electric locomotives, locomotive products and diesel engines for the rail industry. Formerly a division of General Motors, EMD has been owned by Progress Rail since 2010. Electro-Motiv ...
built far more than the others, chiefly its TR (transfer) series. In addition to the transfer duties they were designed for, cow–calf sets were also used in hump yards to send cuts of cars over the hump for classification. The
Union Pacific Railroad The Union Pacific Railroad is a Railroad classes, Class I freight-hauling railroad that operates 8,300 locomotives over routes in 23 U.S. states west of Chicago and New Orleans. Union Pacific is the second largest railroad in the United Stat ...
made use of cow–calf sets as helpers on a steep grade near Kelso, California, until 1959, when the use of multiple-unit train control made them obsolete. Most American examples were replaced by
road switcher A road switcher locomotive is a type of railroad locomotive designed to both haul railroad car, railcars in mainline service and Shunting (rail), shunt them in railroad yards. Both type and term are North American in origin, although similar t ...
locomotives. The Belt Railway of Chicago was the final holdout, continuing to operate TR2 and TR4 sets into the 1980s and 1990s.


List of cow–calf models


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. * EMD TR * EMD TR1 * EMD TR2 * EMD TR3 * EMD TR4 * EMD TR5 * EMD TR6


Other cow–calf models

The
American Locomotive Company The American Locomotive Company (often shortened to ALCO, ALCo or Alco) was an American manufacturer that operated from 1901 to 1969, initially specializing in the production of locomotives but later diversifying and fabricating at various time ...
(ALCO) built two cow–calf sets, derived from the ALCO S-6 and designated ''SSB-9''.
Baldwin Locomotive Works The Baldwin Locomotive Works (BLW) was an American manufacturer of railway locomotives from 1825 to 1951. Originally located in Philadelphia, Pennsylvania, it moved to nearby Eddystone, Pennsylvania, Eddystone in the early 20th century. The com ...
produced nine cow–calf versions of the Baldwin S-8. Both ALCO and Baldwin's cow–calf sets all went to customer Oliver Mining. Cow–calf locomotives in the United Kingdom are generally referred to as ''master and slave'' locomotives. Three sets were created by
British Rail British Railways (BR), which from 1965 traded as British Rail, was a state-owned company that operated most rail transport in Great Britain from 1948 to 1997. Originally a trading brand of the Railway Executive of the British Transport Comm ...
in 1965 by permanently coupling pairs of locomotives dating from 1959 and 1962, the cabs and controls being removed from the calves. They were designated ' and operated at Tinsley Marshalling Yard, the last being withdrawn in 1985. British Steel created some in a similar manner in 1971 for use at Port Talbot Steelworks. Four locomotives built by
Brush Traction Brush Traction was a manufacturer and maintainer of railway locomotives in Loughborough, England whose operations have now been merged into the Wabtec company's Doncaster UK operations. History Hughes' Locomotive & Tramway Engine Wor ...
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.


See also

* Slug (railroad) *
Twin unit A twin unit, twinset, or double unit is a set of two railroad Railway car, cars or locomotives which are permanently coupled and treated as if they were a single unit. A twinset of cars or coaches can also be called a twin car. In US passenger ...


References

{{Reflist Diesel locomotives