The GE U23B Diesel-electric locomotive was introduced by GE Transportation in 1968 as a medium horsepower roadswitcher, featuring a 12 cylinder FDL engine. It was one of the most successful models of the Universal Series, with railroads ordering it from 1968 until 1977 when it was replaced by the B23-7. 481 units were built, including 16 exported to Peru.
Not many U23Bs still exist, but a few shortline and regional railroads still use them in everyday service. The Georgia Central Railway was one of the last U23B holdouts, rostering almost all of the remaining ex Southern Railway (U.S.) high short hood U23Bs. The Georgia Central as of July 2015 has all of its U23Bs off of the roster with the 3965 going to the Southern Appalachia Railway Museum in Oak Ridge, TN.
The Huntsville and Madison County Railroad Authority in Huntsville, AL, operates perhaps one of the last U23B's used in daily freight service, as of October 2015. HMCR 9554 was originally built in late 1974 as L&N 2800. The last U23B built, originally Conrail 2798, and more recently Providence and Worcester 2203, is in regular excursion service at the Naugatuck Railroad, operated by the Railroad Museum of New England in Thomaston, Connecticut.
Western Rail Inc in Airway Heights, WA currently has a U23B that railroad companies can lease. It was used on the Eastern Washington Gateway Railroad as of 2017 for freight service. It is numbered NIWX 2204 and is an ex Northern Illinois and Western locomotive.
|Atchison, Topeka and Santa Fe Railway||49||6300-6348|
|Chesapeake and Ohio Railway||30||2300–2329||Bloomberg trucks|
|Delaware and Hudson Railway||16||301-316|
|Ferrocarril del Pacífico||10||537-546|
|Lehigh Valley Railroad||12||501-512||to Conrail 2777-2788|
|Louisville and Nashville Railroad||90||2708–2772, 2800–2824||FB-2 trucks|
|Missouri Pacific Railroad||39||668-674, 2257–2288||FB-2 trucks|
|Ferrocarriles Nacionales de México||30||9100-9129||9114-9121 AAR type-B trucks, all others FB-2|
|Penn Central Transportation||77||2700–2776||to Conrail 2700-2776|
|Southern Peru Copper||16||40-45, 50-59||FB-2 trucks|
|Southern Railway||70||3900-3969||High-nose, 3900-3914 with AAR type-B trucks, 3935-3969 with FB-2|
|Western Pacific Railroad||15||2251–2265||Bloomberg trucks|