It was the only system to purchase the TR, as well as the following TR1 of 1941 which featured a uniquely interesting long carbody that was based on the NW3; capable of producing 2,700 horsepower (combined), only two sets of the TR1 were built that year, #9250A-9251A/9250B-9251B. However, orders for future models from other railroads soon followed after the war (which delayed production by four years). In 1945 EMD began producing the 2,000-horsepower TR2, which was also based from the NW2 design. In all, 36 examples of this model were built for seven different lines (IC, Belt Railway of Chicago, Burlington, C&NW, Illinois Central, Milwaukee Road, and Southern) 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 (also based from the NW2) that could produce 3,000 horsepower. The unique lashup of this design earned it the nickname as a "herd." The C&O went on to purchase two, three-unit sets of the TR3; #6500ABC-6501ABC. EMD's last three designs of cow-calves were about as successful as the first three with few 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 including the Milwaukee Road (6 sets), C&O (2 sets), Belt Railway of Chicago (5 sets), and Santa Fe (2 sets). Also 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; the Union Pacific (8 sets) and Union Railroad (2 cows, 4 calves).
Finally, there was the TR6 of 1950 based from the SW8. A less powerful design it featured an eight-cylinder, model 567B prime mover that could product 1,600 horsepower. Once again there were few buyers for this transfer model as only the Southern Pacific, which acquired four sets (including EMD's demonstrator), and the Oliver Iron Mining Company (that purchased eight sets) took orders. Just as with booster units in main line service interest in the cow-calf waned since it required the cabless locomotive to always be mated to a "mother." In other words, it wasn't very utilitarian. A good example of this was with Burlington, which once ordered several cow-calves only to later change its mind and return the calves for cabbed units. By the early 1950s no more TR examples were outshopped by Electro-Motive although those that were remained in use for several years, many of which were rebuilt with cabs like the CB&Q's.
For more reading about early EMC switcher locomotives Mike Schafer’s Vintage Diesel Locomotives highlights virtually all of the classic builders and models from Alco PAs to early EMD Geeps. If you’re interested in classic EMDs, or diesels in general, this book gives an excellent general history of both. You might want to also consider the book EMD Locomotives from author Brian Solomon. Solomon's book highlights the history of EMD from its earliest beginnings in the 1920s, to its phenomenal successes in the mid-20th century, and finally its decline into second spot behind General Electric in the late 20th century and eventual sale by General Motors in 2005. The book features 176 pages of EMD history and is filled with excellent photography and illustrations. Finally, Mr. Solomon's Electro-Motive E-Units and F-Units: The Illustrated History of North America's Favorite Locomotives provides an in-depth history of the the builder's classic covered wagons.
The Cow-Calf Line