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Cow-Calf Locomotives: Types, Photos, And More

Last revised: February 15, 2024

By: Adam Burns

The oddly named cow-calf design was released only by Electro-Motive, first built as an experimental prior to World War II.  It was essentially a different name for "A" and "B" (cabless) locomotives, commonly found in the F and E series cab models. 

EMD took the same concept and applied it to its switcher line for use in transfer and yard work by providing a cabless "B" unit mated to an "A." Doing so offered more horsepower and tractive effort without the need of supplying an additional crew. 

As with transfer models offered by other builders, railroads remained largely disinterested in such a specialized locomotive, even for EMD's highly respectable designs rolling out of La Grange at the time. 

Overall, few cow-calves were sold among the seven different types offered although they did prove more successful than similar examples cataloged by other manufacturers.   As the years passed railroads tended to lashup "A's" and "B's" of different models together.  

Photos

Overview

The cow-calf term is unique into itself; technically it is neither a mother-slug (a fully operational locomotive coupled to a unit with no prime mover, only traction motors and/or ballasting for increased tractive effort) nor an actual "B" unit. 

Instead the design refers solely to switchers built by Electro-Motive.  The "cow-calf" designation was not the product of EMD, merely a nickname adopted by train enthusiasts.  

EMD referred to these designs as transfer switchers, the first of which was an experimental.  This unit, numbered 9201 (later changed to #9202) and listed as the T-Model (for Transfer) was a single, center-cab locomotive built in 1936 for Illinois Central, which intended to use it in yard service between Chicago and Markham Yard.

It was constructed by what was then the Electro-Motive Corporation featuring a pair of 900 horsepower, Winton V-12 201-A prime movers with the carbody supplied by the St. Louis Car Company.

Railroad officials were pleased with the model although its unique B-B+B-B wheel arrangement and longer frame caused the unit to develop a sag beneath the cab.  The issue was later resolved by EMD.

In 1940 the first, true cow-calf model was outshopped by EMD; designated class TR (TRansfer), it was based on the popular 1,000 horsepower NW2. 

However, instead of Winton prime movers the locomotive featured EMD's highly reliable 12-cylinder, model 567 power plant.  

The IC was so pleased with this latest design it ultimately purchased three sets, numbered 9203A–9205A/9203B-9205B.

During their long career these cow-calves spent most of their time in yard service pushing long cuts of freight cars over the hump at Markham.

It was the only system to purchase the TR, as well as the following TR1 of 1941.  This particular variant featured a very interesting extended carbody based on the NW3.

It was capable of producing a combined 2,700 horsepower and was essentially an FT in a switcher carbody, even sporting Blomberg trucks; only two sets were built.

In 1945 EMD began production on the 2,000-horsepower TR2, also based from the NW2 but sporting the updated 567A power plant.

The most successful of the series, 36 sets were built for seven different lines by 1949.  In a bit of comedy, names for future cow-calf combinations became even more interesting.

During the summer of that same year (1949) the Chesapeake & Ohio took delivery of the TR3; a three-unit, cow-calf-calf combination, or "herd," which could produce 3,000 horsepower.  

Data Sheets

TR (NW2)

TR1 (FT)

This variant was a stretched version of an NW, essentially an NW3 which Electro-Motive briefly marketed. 

Internally, it was nearly identical to an FT sporting a 567A prime mover capable of producing 1,350 horsepower each.  In addition, it rode on Blomberg trucks.

TR2 (NW2)

TR3 (NW2)

TR4 (SW7)

TR5 (SW9)

TR6 (SW8)

According to Electro-Motive's Operating Manual #2303, the D15A main generator and D27 traction motors were used in NW2's after August, 1949 and in SW7's after October, 1949.

Production Rosters

TR

(Total Built = 3 Sets)

TR1

(Total Built = 2 Sets)

TR2

(Total Built = 36 Sets)

* Sold to Chicago, Burlington & Quincy as #9400A-9400B.

TR3

(Total Built = 2 Sets)

TR4

(Total Built = 15 Sets)

TR5

(Total Built = 10 Sets And 2 Calves)

TR6

(Total Built = 12 Sets)

*  Became Southern Pacific #4600 (A). Order number 4147.

** Became Southern Pacific #4700 (B). Order number 4147.

Sources

• EMD. Operating Manual #2303: 600 & 1200 HP Switching Locomotives (Models SW1 & SW7; 567 Series Engines). La Grange: Electro-Motive Division (General Motors Corporation), January, 1950 (5th Edition).

• Foster, Gerald. A Field Guide To Trains. New York: Houghton Mifflin, 1996.

• Hayden, Bob. Diesel Locomotives: Cyclopedia, Volume 2 (Model Railroader). Milwaukee: Kalmbach Publishing Company, 1980.

• Marre, Louis A. Diesel Locomotives: The First 50 Years, A Guide To Diesels Built Before 1972.  Milwaukee: Kalmbach Publishing Company, 1995.

• Pinkepank, Jerry A. Diesel Spotter's Guide.  Milwaukee: Kalmbach Publishing Company, 1967.

• Solomon, Brian.  EMD Locomotives.  Minneapolis: MBI Publishing Company, 2006.

The C&O went on to purchase two, three-unit sets; #6500ABC-6501ABC.  EMD's last three cow-calf models saw only modest sales:

• In 1950-1951 it released an SW7 version, the TR4 that could produce 1,200 horsepower; 15 examples were built for four different railroads. 


• Later in 1951 EMD cataloged its most powerful cow-calf, the 2,400 horsepower TR5.  Based from the SW9 it utilized the newest model 567B prime mover but only two buyers were interested; Union Pacific and Union Railroad (a short line based in the Pittsburg, Pennsylvania area).


• Finally, there was the TR6 of 1950.  A less powerful version it featured a pair of four-cylinder, model 567B engines which could produce 800 horsepower each.

Once again there were few buyers as only the Southern Pacific, which acquired four sets (including EMD's demonstrator), and the Oliver Iron Mining Company took orders. 

By the early 1950s no more TR examples were outshopped although those that were remained in use for several years, many of which were rebuilt with cabs like the CB&Q's.