A New Haven Railroad freight train led by a U25B locomotive passes Danbury Union Station on the Maybrook Line on July 28, 1968.

(Roger Puta, Public domain, via Wikimedia Commons)



The GE U25B is General Electric's first independent entry into the United States domestic road switcher diesel-electric locomotive railroad 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. In 1956 the GE Universal Series of diesel locomotives was founded for the export market. The U25B was the first attempt at the domestic market since its termination of the consortium agreement with Alco.


ATSF U25B 1614 in a freight stopping at Chillicothe, Illinois to change crews on October 7, 1966.

(Roger Puta, courtesy Marty Bernard, railfan 44, Public domain, via Wikimedia Commons)



The U25B (nicknamed U-Boat) is 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. GE had developed internal combustion-electric generating, control, and drive systems in the early 1920s, which provided the foundation for the use of internal combustion engines in railroading. Early applications were in motorized railcars and switch engines. The 1930s saw that technology adapted to high speed mainline locomotives. In 1940 GE partnered with Alco, who by that time were well-established as a manufacturer of diesel switch engines and were introducing their first diesel road locomotives. They were successful in building locomotives for switching and short-haul applications, having introduced the first road-switcher design in 1941 (which would supplant the carbody design developed by the Electro-Motive Corporation by the mid-1950s) and gained a 26% market share as of 1946. Alco-GE's efforts in main line road locomotives had not been successful at breaking into EMD's dominant position in that market, although they introduced a successful gas turbine-electric locomotive to market in 1952. In 1953 GE went independent from Alco in locomotive production, with their new subsidiary GE Rail taking over the gas turbine-electric venture while they sought a supplier of more reliable diesel engines suitable for road locomotives. Production of Cooper-Bessemer powered Universal Series locomotives began in 1956 and some 400 export locomotives were sold before the U25B was offered in the United States. The U25B was announced by General Electric as a domestic model on April 26, 1960. It was the first locomotive powered by GE's highly successful FDL-16 engine.

The "U-Boat" put GE on the road to becoming the top locomotive producer in the U.S., 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 EMD GP20 (2,000 hp) and the Alco RS27 (2,400 hp or 1,800 kW).

Though many were produced and sold, the only remaining U25B locomotives are in museums, as many were retired or scrapped at the end of their service life by the end of the 1980s.


Southern Pacific M-K TE70-4S No. 7030.

(Craig Garver, Public domain, https://www.flickr.com/photos/digitalrailartist/51755076099/in/dateposted/)



Four Southern Pacific U25Bs were rebuilt by Morrison-Knudsen with a Sulzer V-12 prime mover. These locomotives, designated M-K TE70-4S, operated from 1978 to 1987. The experiment proved unsuccessful and no additional units were rebuilt.


SP 3100, the only GE U25B still in working order. (Pretzelpaws at en.wikipedia, CC BY-SA 3.0 <http://creativecommons.org/licenses/by-sa/3.0/>, via Wikimedia Commons)


Long hood end of SP 3100. (Pretzelpaws at en.wikipedia, CC BY-SA 3.0 <http://creativecommons.org/licenses/by-sa/3.0/>, via Wikimedia Commons)

The manufacturer's plate on the 3100. (Pretzelpaws at en.wikipedia, CC BY-SA 3.0 <http://creativecommons.org/licenses/by-sa/3.0/>, via Wikimedia Commons)


Six U25Bs are known to be preserved today. Of these, only one remains in operating condition. Southern Pacific 3100 is now on permanent exhibit at the Orange Empire Railway Museum (now known as the Southern California Railway Museum) in Perris, California. Built in 1963, this locomotive was first numbered SP 7508. Later numbered SP 6800, it became a goodwill ambassador for the railroad in 1976 when it was painted in an elaborate red, white, and blue color scheme in celebration of the nation's bicentennial; it was later renumbered and repainted in standard SP livery and was donated to the museum. The 3100 is fully certified to run on any of the nation's railroads and is frequently used as motive power for offsite work trains.


PRR 2615, a GE U25B in the yard at Logansport, IN, November 25, 1966.

(Roger Puta, courtesy Marty Bernard, railfan 44, Public domain, via Wikimedia Commons)


Several more examples survive, all in varying states of preservation:

  • Louisville and Nashville 1616 is stored at the Southern Appalachia Railway Museum in Oak Ridge, Tennessee. The unit is missing its main generator.
  • Milwaukee Road 5056 is preserved at the Illinois Railway Museum and is being both cosmetically and mechanically restored for operation on the museum grounds.
  • Milwaukee Road 5057 is being cosmetically restored by Cascade Rail Foundation to eventually be displayed at the South Cle Elum Rail Yard in Washington.
  • New Haven 2525 has been preserved by the Railroad Museum of New England/Naugatuck Railroad of Thomaston, CT. It wears its original New Haven colors, however it is not currently operational.
  • New York Central 2500 is on display at the Lake Shore Railway Historical Society museum in North East, Pennsylvania.


Original owners

Railroad Quantity Road Numbers Notes
General Electric (XP-24 testbed) 2 751–752 Never sold, retained by GE
General Electric (demonstrator) 4 753–756 High short hood; to Frisco 804–807
General Electric (demonstrator) 4 2501–2504 to Union Pacific 633–636
General Electric (demonstrator) 4 51-54 to Frisco 812, 814, 815, and 813.
Atchison, Topeka and Santa Fe Railway 16 1600–1615 renumbered 6600–6615
Chesapeake and Ohio Railway 38 2500–2537 renumbered 8100–8137
Chicago, Burlington and Quincy Railroad 6 100–105 to Burlington Northern 5424–5429
Chicago, Milwaukee, St. Paul and Pacific Railroad ("Milwaukee Road") 12 380–391 380 retired 1966; remainder renumbered 5000–5010; renumbered 5050–5060
Chicago, Rock Island and Pacific Railroad 39 200–238 225–238 to Maine Central Railroad 225–238
Erie Lackawanna Railroad 27 2501–2527 to Conrail 2570–2596
Great Northern Railway 24 2500–2523 to Burlington Northern 5400–5423
Louisville and Nashville Railroad 27 1600–1626
New York Central Railroad 70 2500–2569 to Penn Central 2500–2569; to Conrail 2500–2569
New York, New Haven and Hartford Railroad 26 2500–2525 to Penn Central 2660–2685; to Conrail 2660–2685
Norfolk and Western Railway 1 3515 3515 was renumbered to 8138 (wreck replacement for Wabash unit)
Pennsylvania Railroad 59 2500–2548, 2649–2658 renumbered 2600–2658; to Penn Central 2600–2658; to Conrail 2600–2658
St. Louis – San Francisco Railway ("Frisco") 24 800–803, 808–811, 816-831 804–807, 812-815 ex GE. Numbers 800–807 were high short hood units in black and yellow scheme; The next set (808–815) were low short hood units in black and yellow. The last 16, 816–831, were low hoods and delivered in the orange and white scheme. To Burlington Northern 5210–5233.
Southern Pacific Company 68 7500–7567 renumbered 6700–6767
Union Pacific Railroad 12 625–632, 637–640 633–636 ex GE demonstrators 2501–2504. The only railroad, other than the Frisco, to have high short hood U25Bs.
Wabash Railroad 15 500–514 to Norfolk and Western 3516–3529; renumbered 8139–8152
Total 478


Type and origin
Power type: Diesel-electric
Builder: GE Transportation Systems
Model: U25B
Build date: April 1959 – February 1966
Total produced: 478
​• AAR B-B
Gauge: 4 ft 8+1⁄2 in (1,435 mm) standard gauge
Prime mover: GE FDL-16
Transmission: Diesel electric
Performance figures
Power output: 2,500 hp (1,900 kW)
Disposition: most scrapped, a few in preservation