rail transport Rail transport (also known as train transport) is a means of transport that transfers passengers and goods on wheeled vehicles running on rails, which are incorporated in Track (rail transport), tracks. In contrast to road transport, where the ...

, a cow-calf (also cow and calf) locomotive is a set of

switcher A switcher, shunter, yard pilot, switch engine, yard goat, or shifter is a small railroad locomotive used for manoeuvring railroad cars inside a rail yard in a process known as ''switching'' (US) or ''shunting'' (UK). Switchers are not inte ...

-type

diesel locomotive A diesel locomotive is a type of railway locomotive in which the prime mover is a diesel engine. Several types of diesel locomotives have been developed, differing mainly in the means by which mechanical power is conveyed to the driving whe ...

s. The set usually is a pair; some 3-unit sets (with two calves, also known as herds) were built, but this was rare. A cow is equipped with a driving cab; a calf is not. The two are coupled together (either with regular couplers or a semi-permanent drawbar) and are connected with MU cables and brake lines so that both locomotive units can be operated from the single cab. Cows are analogous to A units and calves to

B unit B, or b, is the second letter of the Latin-script alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''bee'' (pronounced ), plural ''bees''. It re ...

road locomotives. Both have prime movers. Like the early EMD FT locomotives, the Cow-calf sets were typically built as mated pairs, with the Cow (or cabbed unit) and calf (or cabless unit) sharing a number. However this was not always the case, with over time many of the sets being broken up and couplers added to aid with versatility. Cow-calf locomotives can be distinguished from the sometimes very similar looking slug and slug mother sets by the fact that both cows and calves are independently powered, while slugs are engineless, and dependent on power from their "mother" units.

Distinctions between cow-calf, B units, and slugs

Cow-calf sets 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 sm ...

and especially B units. They differ from both in that a B unit is designed to operate with any other locomotives, while cow-calf sets are meant to be semi-permanently coupled to each other and operated together, 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 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, the cow referred to the locomotive equipped with a cab, while calves lacked a cab. Cow-calf sets with two calves are known as "herds"; the only example of these 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 P. Huntington, it reached from Virginia's capital city of Richmond ...

. The cow, calf, and herd designations were nicknames and not official. Cow-calf locomotives were designed for both 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' Electro-Motive Division 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 , legally Union Pacific Railroad Company and often called simply Union Pacific, is a freight-hauling railroad that operates 8,300 locomotives over routes in 23 U.S. states west of Chicago and New Orleans. Union Pac ...

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 Multiple-unit train control, sometimes abbreviated to multiple-unit or MU, is a method of simultaneously controlling all the traction equipment in a train from a single location—whether it is a multiple unit comprising a number of self-powered ...

made them obsolete. Most American examples were replaced by road switcher locomotives, which could both handle switching duties and haul mainline trains. The

Belt Railway of Chicago The Belt Railway Company of Chicago , headquartered in Bedford Park, IL, is the largest switching terminal railroad in the United States. It is co-owned by six Class I railroads — BNSF Railway, Canadian National Railway, Canadian Pacific R ...

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 EMD may refer to: Finance and commerce * Emerging market debt * Earnest money deposit, in the United States, a security deposit, especially for real estate Medicine * Electromagnetic diaphragm * Electromechanical dissociation * Emergency med ...

Other cow-calf models

The

American Locomotive Company The American Locomotive Company (often shortened to ALCO, ALCo or Alco) was an American manufacturer of locomotives, diesel generators, steel, and tanks that operated from 1901 to 1969. The company was formed by the merger of seven smaller locomo ...

(ALCO) built two cow-calf sets, derived from the ALCO S-6 and designated SSB-9. Baldwin Locomotive Works produced nine cow-calf versions of the

Baldwin S-8 The BLH S8 was an diesel-electric switcher locomotive. The Baldwin-Lima-Hamilton Corporation produced a total of 63 units (61 for United States railroads and 2 for use in Cuba) between 1951 and 1953. Of these, nine were "calf Calf most often r ...

. Both ALCO and Baldwin's cow-calf sets all went to customer Oliver Mining. Three pairs of cow-calf locomotives were built in the United Kingdom in the 1960s by combining two British Rail Class 08 locomotives together, these were designated the British Rail Class 13.

References

{{DEFAULTSORT:Cow-Calf Diesel locomotives