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 GE Universal Series started production in 1956 and some 400 export locomotives were sold before the U25B was offered in the United States.
The U25B put GE on the road to becoming the major producer in the U.S., much to the consternation of EMD. It introduced many innovations to the diesel locomotive market, including the 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 (2,400 hp or 1,800 kW).
The only remaining U25B locomotives are in museums, as the majority were retired or scrapped at the end of their service life in the 1980s.