Green Bay and Western Railroad 2407, an ALCO RSD-15, at the Illinois Railway Museum, July, 2005.

(Sean Lamb (User:Slambo), CC BY-SA 2.5 <>, via Wikimedia Commons)


Alco rectangular block logo bw.


The ALCO RSD-15 is a diesel-electric locomotive built by the American Locomotive Company (ALCO) of Schenectady, New York between August 1956 and June 1960, during which time 75 locomotives were produced. The RSD-15 was powered by an ALCO 251 16-cylinder four-cycle V-type prime mover rated at 2,400 horsepower (1.79 MW); it superseded the almost identical ALCO 244-engined RSD-7, and was catalogued alongside the similar but smaller 1,800 hp (1.34 MW) RSD-12, powered by a 12-cylinder 251-model V-type diesel engine.

The locomotive rode on a pair of three-axle Trimount trucks with all axles powered by General Electric model 752 traction motors. These trucks have an asymmetrical axle spacing because of the positioning of the traction motors. The six-motor design allowed higher tractive effort at lower speeds than an otherwise similar four-motor design.

The RSD-15 could be ordered with either a high or low short hood; railfans dubbed the low short hood version "Alligators", due to their unusually long low noses.


Santa Fe Alco RSD-15 No. 840, part of the power consist pulling Train No. 2, the San Francisco Chief at Caliente, CA, August 26, 1967.

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



A single example of the very similar model RSD-17 was built by the Montreal Locomotive Works in 1957. After demonstrating on the Canadian Pacific (as No. 7007), the Canadian National (as No. 3899), and the Pacific Great Eastern (as No. 624), the locomotive was purchased by the Canadian Pacific (as No. 8921). Nicknamed "The Empress of Agincourt", by Pete Fairfull, who was its primary operator for many years, (for its common presence around Toronto's Agincourt yard), the locomotive served the railway until 1995, when truck problems forced its retirement.


RSD-17 locomotive in Elgin County Railway Museum, St. Thomas, Ontario.

(Balcer, Public domain, via Wikimedia Commons)


Original owners

Railroad Quantity Road numbers Notes
Atchison, Topeka and Santa Fe Railway 50 800–849 Low nose
Duluth, Missabe and Iron Range Railroad 6 50–55 Later Bessemer and Lake Erie Railroad 881-886 Cartier acquired the six units (91-96) 6/1972. All 6 units were converted to low hoods. No. 96 in service as Susquehanna and Maryland RR (SMD) No. 96
Pennsylvania Railroad 6 8611–8616 Later Penn Central 6811–6816. Conrail rebuilt four of them to MT6s 1125-1128. After the dividing of Conrail, 2 went to CSX as 1017 and 1018, and 2 went to Norfolk Southern as 1114 and 1115.
Southern Pacific Railroad 3 250–252 Low nose
St. Louis Southwestern Railway 10 5150–5159 Low nose
Canadian Pacific Railway 1 8921 RSD-17

Austin & Texas Central ALCO RSD-15 No. 442 near the Austin Convention Center.

(Rvassar, CC BY-SA 3.0 <>, via Wikimedia Commons)


Surviving examples

Five RSD-15s survive in preservation; all are ex-Santa Fe units.

• Santa Fe No. 843 is preserved at the Arkansas Railroad Museum in Pine Bluff, Arkansas.

• Santa Fe No. 9820 is preserved at the California State Railroad Museum in Sacramento, but is not publicly displayed.

• Austin and Texas Central No. 442 (ex-ATSF No. 842) is preserved and operable at the Austin Steam Train Association (ASTA) in Cedar Park, Texas. It's painted in a modified Southern Pacific "Black Widow" scheme. While No. 442 is operable, it is currently sidelined awaiting installation of Positive Train Control (PTC).

Green Bay and Western No. 2407 (ex-ATSF No. 841) is preserved and operational at the Illinois Railway Museum.

• Utah Railway No. 401 (ex-ATSF No. 823) is preserved at the Utah State Railroad Museum in Ogden, Utah.

• The RSD-17 demonstrator, Canadian Pacific No. 8921, is preserved at the Elgin County Railway Museum, St. Thomas, Ontario, Canada.


Cotton Belt 850. Text from the postcard reads: St. Louis and Southwestern's Alco DL-600B low nose "Alligator" No. 850 rests in Memphis after having brought tonnage in across the Mississippi River from Brinkley, AR. December 6, 1965. Photo by William I. White, Jr. (Audio-Visual Designs, Earlton, NY, Public domain, via the W. Lenheim Collection)



  • The RSD-15 has been produced in N scale by Mehano of Yugoslavia and Broadway Limited of the United States.
  • The RSD-15 has been produced in HO scale by Broadway Limited Imports and handmade brass. Alco Models (DL600b) high and Low hoods. Also (Overland Models).
  • The RSD-15 has been produced in O scale by Atlas O in their Trainman line.
  • The RSD-17 has not been mass-produced in any scale; however, in 2008 Broadway Limited Imports did produce a limited run of the high-hood CP 8921 in HO scale.



Type and origin
Power type: Diesel-electric
Builder: Alco
Model: DL600B
Build date: August 1956 - June 1960
Total produced: 75
​• AAR C-C
• UIC Co′Co′
Gauge: 4 ft 8+1⁄2 in (1,435 mm) standard gauge
Trucks: Alco trimount
Wheel diameter: 40 in (1,016 mm)
Length: 66 ft 7 in (20.29 m)
Width: 10 ft 2 in (3.10 m)
Height: 14 ft 11 in (4.55 m)
Locomotive weight: 335,000 lb (151,953.4 kg)
Fuel capacity 3,350 US gallons (12,700 L; 2,790 imp gal)
Prime mover: Alco 251B
Engine type: V16 Four-stroke diesel
Generator: GE GT586
Traction motors: GE 752 (6x)
Cylinders: 16
Performance figures
Maximum speed: 65 mph (105 km/h)
Power output: 2,400 hp (1.79 MW)
Tractive effort Starting: 95,600 lbf (425.2 kN) at 25% adhesion;
Tractive effort Continuous: 79,500 lbf (353.6 kN) at 12 mph (19 km/h)