The GE U25C was the builder's first entry into the six-axle locomotive market, first built during the early 1960s a few years after the company had released its first production locomotive in the United States, the U25B. This initial model, and the following U28C, sold rather poorly for General Electric (although several Class Is did experiment with and purchase a few units). Much of this can likely be attributed to two things; first, while GE had collaborated with other companies in the industry for decades (such as the American Locomotive Company) it had never built its own locomotives; and second was the fact that many simply were not yet interested in six-axle designs. However, future models like the U30C and U33C sold quite well for the company as railroads began to embrace and see the benefits of powerful six-axle locomotives. After the mid-1970s nearly all domestic-built GE diesel locomotives were of the C-C variety.
The GE U25C first began production in September, 1963, four years following the production of the U25B, its four-axle cousin. At the time of its production many were still reluctant to use six-axle, high-horsepower diesel locomotives in main line freight service so GE had a tough time making a case for the U25C even though it featured reliability and straightforward design features which the company became well known for. Utilizing GE's 4-cycle model FDL16 the U25C could produce 2,500 horsepower. Since the unit featured a C-C design it not only provided more traction but also could be operated on light or secondary lines as its weight could be more evenly distributed over the rails.
The classification for the GE's six-axle designs are quite similar to its four-axles. For instance, in the case of the U25C; "U" regarded its Universal line, "25" was the first two digits of its horsepower rating, and "C" described its powered axle rating (C-C). At 60 feet, 2 inches in length the U25C was actually the same length as the four axle U25B. However, beginning with the U28C GE began increasing the length of its C-C road switchers (and they continued to grow with the U30C through U36C). All of the locomotive's internal equipment including main/auxiliary generators and traction motors were all constructed by GE itself while air equipment was supplied from Westinghouse Electric.
The most noticeable benefits of the U25C was, as mentioned above, its starting tractive effort rating of 90,000 pounds nearly 17% higher than with the U25B. This allowed the locomotive to get trains started much faster. While railroads were still reluctant to purchase high-horsepower six-axle locomotives at the time within a few years they began to come around as GE would sell more and more such models following the U28C, U30C, U33C, and U36C (combined, these models would sell well over 1,000 examples). By the time production on the GE U25C had ended in December, 1965 some 113 units had been sold six different Class Is including the Atlantic Coast Line (21); Burlington (12), Lake Superior & Ishpeming (2), Louisville & Nashville (18), Northern Pacific (30), Pennsylvania (20), and ten that were purchased for the Oro Dam in California (these units later went to the L&N). Today, at least one GE U25C is known to be preserved, LS&I #2501, still owned by the railroad since it was bought new in 1964 and on display in Marquette, Michigan.
For more reading about GE's U-boat line the bookU-Boats: General Electric's Diesel Locomotive by author Greg McDonnell provides a complete history of the company's first production diesel models. Also, noted historian Brian Solomon has authored a number of books covering the history and background of GE's locomotives. Two, which provide a general but thorough coverage include GE Locomotives and GE And EMD Locomotives: The Illustrated History. As with virtually all of Mr. Solomon's you can expect a well-written title with large, crisp, and sharp photographs.