Cow-Calf Locomotives: Types, Photos, And More

Last revised: March 6, 2022

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.  

A Chicago & North Western photo featuring TR-2 cow-calf set #2001-A and #2001-B in October of 1949. As built these locomotives were used in hump yard service in Chicago. Later, calf #2001-B was rebuilt into Slug #BU-5 during 1961.


A Brief History Of The Cow-Calf Design

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.

Chicago Great Western cow-calf switcher set TR2, #61-61A, are seen here between assignments at what is most likely St. Paul, Minnesota during the mid-1960s. American-Rails.com collection.

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.  


TR (NW2) Data Sheet

Entered Production2/1940 (Illinois Central #9203)
Years Produced2/1940 - 11/1940
EMD ClassTR
Engines (2)567 (6 Cylinder)
Engine BuilderGM/EMD
Horsepower2000
RPM800
Length44' 5" (Per Locomotive)
Height (Top Of Rail To Top Of Cab)14' 4 5/8"
Width10' 0"
Weight248,000 Lbs
Fuel Capacity600 Gallons
Air Compressor3C2C (Westinghouse)
Air Brake Schedule24EL (Westinghouse)
TrucksB-B
Truck TypeGRS Rigid Bolster, Drop-Side Equalizer (AAR Type-A)
Truck Wheelbase8' 0"
Wheel Size40"
Traction Motors (Per Locomotive)D37 (4), GM/EMD
Traction GeneratorD15C, GM/EMD
Auxiliary GeneratorGeneral Motors/EMD
MU (Multiple-Unit)Yes
Dynamic BrakesNo
Gear Ratio62:15
Tractive Effort/Starting62,500 Lbs
Tractive Effort/Continuous31,000 Lbs at 11.0 mph
Top Speed65 mph

TR1 (FT) Data Sheet

Entered Production4/1941 (Illinois Central #9250-9251)
Years Produced4/1941 - 5/1941
EMD ClassTR
Engines (2)567 (8 Cylinder)
Engine BuilderGM/EMD
Horsepower2700
RPM800
Length52' 1 1/2" (Per Locomotive)
Height (Top Of Rail To Top Of Cab)14' 4 5/8"
Width9' 11 1/2"
Weight230,000 Lbs
Fuel Capacity600 Gallons
Air Compressor3C2C (Westinghouse)
Air Brake Schedule24EL (Westinghouse)
TrucksB-B
Truck TypeBlomberg
Truck Wheelbase9' 0"
Wheel Size40"
Traction Motors (Per Locomotive)D7 (4), GM/EMD
Traction GeneratorD12, GM/EMD
Auxiliary GeneratorGeneral Motors/EMD
MU (Multiple-Unit)Yes
Dynamic BrakesNo
Gear Ratio62:15
Tractive Effort/Starting55,000 Lbs
Tractive Effort/Continuous40,000 Lbs at 9.3 mph
Top Speed65 mph

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) Data Sheet

Entered Production11/1945 (Illinois Central #9206A-9206B)
Years Produced11/1945 - 12/1949
EMD ClassTR2
Engines (2)567A (6 Cylinder)
Engine BuilderGM/EMD
Horsepower2000
RPM800
Length44' 5" (Per Locomotive)
Height (Top Of Rail To Top Of Cab)14' 4 5/8"
Width10' 0"
Weight248,000 Lbs
Fuel Capacity600 Gallons
Air Compressor3C2C (Westinghouse)
Air Brake Schedule24EL (Westinghouse)
TrucksB-B
Truck TypeGRS Rigid Bolster, Drop-Side Equalizer (AAR Type-A)
Truck Wheelbase8' 0"
Wheel Size40"
Traction Motors (Per Locomotive)D37 (4), GM/EMD
Traction GeneratorD15C, GM/EMD
Auxiliary GeneratorGeneral Motors/EMD
MU (Multiple-Unit)Yes
Dynamic BrakesNo
Gear Ratio62:15
Tractive Effort/Starting62,500 Lbs
Tractive Effort/Continuous31,000 Lbs at 11.0 mph
Top Speed65 mph

TR3 (NW2) Data Sheet

Entered Production7/1949 (Chesapeake & Ohio #6500)
Years Produced7/1949 - 10/1949
EMD ClassTR3
Engines (3)567A (6 Cylinder)
Engine BuilderGM/EMD
Horsepower3000
RPM800
Length44' 5" (Per Locomotive)
Height (Top Of Rail To Top Of Cab)14' 4 5/8"
Width10' 0"
Weight248,000 Lbs
Fuel Capacity600 Gallons
Air Compressor3C2C (Westinghouse)
Air Brake Schedule24EL (Westinghouse)
TrucksB-B
Truck TypeGRS Rigid Bolster, Drop-Side Equalizer (AAR Type-A)
Truck Wheelbase8' 0"
Wheel Size40"
Traction Motors (Per Locomotive)D37 (4), GM/EMD
Traction GeneratorD15C, GM/EMD
Auxiliary GeneratorGeneral Motors/EMD
MU (Multiple-Unit)Yes
Dynamic BrakesNo
Gear Ratio62:15
Tractive Effort/Starting62,500 Lbs
Tractive Effort/Continuous31,000 Lbs at 11.0 mph
Top Speed65 mph

TR4 (SW7) Data Sheet

Entered Production6/1950 (Chesapeake & Ohio #6000A)
Years Produced6/1950 - 1/1951
EMD ClassTR4
Engines (2)567A (6 Cylinder)
Engine BuilderGM/EMD
Horsepower2400
RPM800
Length44' 5" (Per Locomotive)
Height (Top Of Rail To Top Of Cab)14' 6"
Width10' 2"
Weight248,000 Lbs
Fuel Capacity600 Gallons
Air CompressorWXO (GM/EMD)
Air Brake Schedule24EL (Westinghouse)
TrucksB-B
Truck TypeGRS Rigid Bolster, Drop-Side Equalizer (AAR Type-A)
Truck Wheelbase8' 0"
Wheel Size40"
Traction Motors (Per Locomotive)D37 (4), GM/EMD
Traction GeneratorD15C, GM/EMD
Auxiliary GeneratorGeneral Motors/EMD
MU (Multiple-Unit)Yes
Dynamic BrakesNo
Gear Ratio62:15
Tractive Effort/Starting62,000 Lbs
Tractive Effort/Continuous36,000 Lbs at 11.0 mph
Top Speed65 mph

TR5 (SW9) Data Sheet

Entered Production3/1951 (Union Railroad #701-702)
Years Produced3/1951 - 10/1951
EMD ClassTR5
Engines (2)567B (6 Cylinder)
Engine BuilderGM/EMD
Horsepower2400
RPM800
Length44' 5" (Per Locomotive)
Height (Top Of Rail To Top Of Cab)14' 6.5"
Width9' 11 1/2"
Weight248,000 Lbs
Fuel Capacity600 Gallons
Air CompressorWXO (GM/EMD)
Air Brake Schedule6BL (Westinghouse)
TrucksB-B
Truck TypeGRS Rigid Bolster, Drop-Side Equalizer (AAR Type-A)
Truck Wheelbase8' 0"
Wheel Size40"
Traction Motors (Per Locomotive)D37 (4), GM/EMD
Traction GeneratorD15C, GM/EMD
Auxiliary GeneratorGeneral Motors/EMD
MU (Multiple-Unit)Yes
Dynamic BrakesNo
Gear Ratio62:15
Tractive Effort/Starting62,000 Lbs
Tractive Effort/Continuous43,000 Lbs at 11.0 mph
Top Speed65 mph

TR6 (SW8) Data Sheet

Entered Production11/1950 (Electro-Motive #1600-1600B)
Years Produced11/1950 - 8/1953
EMD ClassTR6
Engines (2)567B (4 Cylinder)
Engine BuilderGM/EMD
Horsepower1600
RPM800
Length44' 5" (Per Locomotive)
Height (Top Of Rail To Top Of Cab)14' 6 1/4"
Width9' 11 2/3"
Weight230,000 Lbs
Fuel Capacity600 Gallons
Air CompressorWXO (Gardner-Denver)
Air Brake Schedule6BL (Westinghouse)
TrucksB-B
Truck TypeGRS Rigid Bolster, Drop-Side Equalizer (AAR Type-A)
Truck Wheelbase8' 0"
Wheel Size40"
Traction Motors (Per Locomotive)D37 (4), GM/EMD
Traction GeneratorD15C, GM/EMD
Auxiliary GeneratorGeneral Motors/EMD
MU (Multiple-Unit)Yes
Dynamic BrakesNo
Gear Ratio62:15
Tractive Effort/Starting57,000 Lbs
Tractive Effort/Continuous36,000 Lbs at 11.0 mph
Top Speed65 mph


TR Production Roster (Total Built = 3 Sets)

Owner Road Number Serial Number Order Number Completion Date Quantity
Illinois Central9203-9204 (A-B)1032-1033E2862/19402
Illinois Central9205 (A-B)1190E34511/19401

TR1 Production Roster (Total Built = 2 Sets)

Owner Road Number Serial Number Order Number Completion Date Quantity
Illinois Central9250-9251 (A-B)1191E3584/1941-5/19412

TR2 Production Roster (Total Built = 36 Sets)

Owner Road Number Serial Number Order Number Completion Date Quantity
Illinois Central9206A (A), 9206B (B)2067-2068E55211/19452
Southern Railway2400A-2403A (A)4764-4767E8298/19474
Southern Railway2400B-2403B (B)4768-4771E8298/19474
Southern Railway2404A (A), 2404B (B)5002-5003E8298/19472
Electro-Motive (Demonstrator)912A (A), 912B (B)*5514-5515E91210/19472
Chicago, Burlington & Quincy9401A-9405A (A)6563-6567E10092/19495
Chicago, Burlington & Quincy9401B-9405B (B)6568-6572E10092/19495
Chicago, Burlington & Quincy9406A-9408A (A)6573-6575E10092/1949-3/19493
Chicago, Burlington & Quincy9406B-9408B (B)6576-6578E10092/1949-3/19493
Chicago, Burlington & Quincy9409A (A), 9409B (B)6579-6580E10093/19492
Chicago Great Western58A (A), 58B (B)6877-6878E10978/19482
Chicago Great Western59A-65A (A)6879-6885E10337/1949-8/19497
Chicago Great Western59B-65B (A)6886-6892E10337/1949-8/19497
Chicago Great Western66A (A), 66B (B)6893-6894E10337/19492
Milwaukee Road2000A (A), 2000B (B)7919-7920E112412/19492
Chicago, Burlington & Quincy9410A-9413A (A)8505-8508E117911/19494
Chicago, Burlington & Quincy9410B-9411B (B)8509-8510E117911/19492
Chicago, Burlington & Quincy9412B-9413B (B)8598-8599E117911/19492
Chicago & North Western2000A-2001A (A)10021-10022E130510/19492
Chicago & North Western2000B-2001B (B)10023-10024E130510/19492
Illinois Central9207A (A), 9207B (B)10056-10057600712/19492
Illinois Central9208A (A), 9208B (B)10058-10059600712/19492
Belt Railway Of Chicago500A-501A (A)10512-10513602711/1949-12/19492
Belt Railway Of Chicago500B-501B (B)10514-10515602711/1949-12/19492

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

TR3 Production Roster (Total Built = 2 Sets)

Owner Road Number Serial Number Order Number Completion Date Quantity
Chesapeake & Ohio6500A (A)1025360187/19491
Chesapeake & Ohio6500C, 6500B (B)10254-1025560187/19492
Chesapeake & Ohio6501A (A)10256601810/19491
Chesapeake & Ohio6501C, 6501B (B)10257-10258601810/19492

TR4 Production Roster (Total Built = 15 Sets)

Owner Road Number Serial Number Order Number Completion Date Quantity
Belt Railway of Chicago502A-506A (A)10516-1052040329/19505
Belt Railway of Chicago502B-506B (B)10521-1052540329/19505
Milwaukee Road2001A (A)1140240519/19501
Milwaukee Road2001B (B)1140340519/19501
Chesapeake & Ohio6000A (A)1194561246/19501
Chesapeake & Ohio6000B (B)1194661246/19501
Chesapeake & Ohio6001A (A)1194761246/19501
Chesapeake & Ohio6001B (B)1194861246/19501
Santa Fe2418 (A)1236061466/19501
Santa Fe2418A (B)1236161466/19501
Milwaukee Road2002A-2006A (A)12447-1245140711/19515
Milwaukee Road2002B-2006B (B)12452-1245640711/19515
Santa Fe2419 (A)1382762141/19511
Santa Fe2419A (B)1382862141/19511

TR5 Production Roster (Total Built = 10 Sets And 2 Calves)

Owner Road Number Serial Number Order Number Completion Date Quantity
Union Railroad701-702 (A)8544-8545E11873/19512
Union Railroad701C-702C (B)8546-8547E11873/19512
Union Railroad703C-704C (B)14786-14787625310/19512
Union Pacific1870A-1877A (A)15068-1507562849/1951-10/19518
Union Pacific1870B-1877B (B)15076-1508362849/1951-10/19518

TR6 Production Roster (Total Built = 12 Sets)

Owner Road Number Serial Number Order Number Completion Date Quantity
Electro-Motive (Demonstrator)1600 (A)*135491505111/19501
Electro-Motive (Demonstrator)1600B (B)**135501505111/19501
Oliver Iron Mining Company1207A-1209A (A)14829-14831632110/1951-12/19513
Oliver Iron Mining Company1207B-1209B (B)14832-14834632110/1951-12/19513
Oliver Iron Mining Company1210A-1211A (A)14835-14836633212/19512
Oliver Iron Mining Company1210B-1211B (B)14837-14838633212/19512
Southern Pacific4601-4603 (A)15084-15086410010/19513
Southern Pacific4701-4703 (B)15117-15119410010/19513
Oliver Iron Mining Company1212A (A)1705263825/19521
Oliver Iron Mining Company1212B (B)1705363825/19521
Oliver Iron Mining Company1213A (A)1705463825/19521
Oliver Iron Mining Company121BA (B)1705563825/19521
Oliver Iron Mining Company1216A (A)1861965028/19531
Oliver Iron Mining Company1216B (B)1862065028/19531

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

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

Sources:

  • 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.

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