Introduced in 1960, the GE U25B was General Electric's first independent entry into the United States domestic diesel electric locomotive market for heavy production road locomotives since 1936. From 1940 through 1953, GE participated in a design, production, and marketing consortium (Alco-GE) for diesel-electric locomotives with the American Locomotive Company; the U25B was developed following the termination of the consortium agreement.

The U25B (nicknamed U-Boat) was the first commercially successful domestic diesel electric road locomotive designed, built, and sold by General Electric after its split with the American Locomotive Company (Alco), a company dating back to the steam era. Along with Ingersoll-Rand, GE built the first viable American diesel-electric locomotive in 1928. GE had previously produced a number of prototype diesel switchers, in part with Alco.

The U-Boat put GE on the road to becoming the top locomotive producer in the US, much to the chagrin of EMD. It introduced many innovations to the U.S. diesel locomotive market, including a pressurized car body and a centralized air processing system that provided filtered air to the engine and electrical cabinet, thus reducing maintenance. The U25B was also the highest-horsepower four-axle diesel road locomotive in the U.S. at the time of its introduction, its contemporaries being the GP20 (2000 hp) and the RS27 (2400 hp).

Milwaukee 5057 was part of a diesel engine instruction program at Webster Technical College in Sidney Nebraska before donation to the Feather River Rail Society in 1991.  The 5057 has recently been declared to not fit the mission statement of the Feather River Rail Society, and is currently available for preservation by another qualified rail preservation organization.  Contact the FRRS Board of Directors for details.  The 5057 is currently out of service, however, it can be made operational with relatively minor repairs.