Ferrocarril del Pacifico 504 in Nogales, Sonora, Mexico, in March 1979.

(Clay Gilliland, CC BY-SA 2.0 <https://creativecommons.org/licenses/by-sa/2.0>, via Wikimedia Commons)



The ALCO RSD-12 was a C-C diesel-electric locomotive rated at 1,800 horsepower (1.34 MW) produced by the American Locomotive Company (ALCO). 171 locomotives were produced. They were used in much the same manner as its four-axle counterpart, the ALCO RS-11, though the six-motor design allowed better tractive effort at lower speeds.


Southern Pacific Alco RSD12 2950 at Bly, Oregon, October 5, 1975. Photographer unknown. This engine has been retired and is shown as leased to the Oregon California & Eastern. (Craig Garver, Public domain, https://www.flickr.com/photos/digitalrailartist/50785309701/)


Southern Pacific Alco RSD12 7016 at Bakersfield, California, October 13, 1962. Photographer: Neil Shankweiler. (Craig Garver, Public domain, https://www.flickr.com/photos/digitalrailartist/50785146441/)

Original buyers

Railroad Quantity Road numbers Notes
Chesapeake and Ohio Railway 10 6700–6709 Renumbered 2007–2016, 2014 and 2016 were sold to Baltimore and Ohio Railroad, then were purchased by Utah Railway on February 23, 1976.
Lake Superior and Ishpeming Railroad 4 1801–1804
New York, Chicago and St. Louis Railroad (“Nickel Plate Road”) 9 325–333 to Norfolk and Western Railway 2325-2333 in 1964.
Pennsylvania Railroad 25 8655–8679 to Penn Central 6855–6879; then to Conrail 1101-1123 and rebuilt into Alco mt6. 14 went to Norfolk Southern and 9 to CSX 1006-1016 with two retired upon Conrail purchase. All retired in 2020.
Southern Pacific Company 21 7000–7020 Renumbered 2950–2970, rebuilt from RSD-5 locomotives with a new motor and carbody, retaining generators and trucks.
Ferrocarril del Pacífico 19 1502–1508, 509–520
Ferrocarriles Nacionales de México 73 7400–7472
Companhia Siderúrgica Nacional (Brazil) 10 3501–3510 Built by MLW, 1,600 mm (5 ft 3 in); to RFFSA pt: ALCo RSD-12.

ALCO RSD-12 No. 1804 of the Lake Superior & Ishpeming Railroad resting in a shipyard

in Escanaba Michigan in 2010. Ed's note: Sadly, that might be "eternal rest".

(Espeeac12, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons)



Nickel Plate Road No. 329 is preserved at a museum in Bellevue, Ohio.

Southern Pacific No. 2954 and No. 2958 are preserved at the Southern California Railroad Museum in Perris, California. Both of these units are rebuilt from RSD-5s.

• Paperton Junction Southern (ex-SP No. 2962) is preserved at the Arkansas Railroad Museum in Pine Bluff, Arkansas.

Lake Superior & Ishpeming No. 1804 partially survives in a shipyard in Escanaba, Michigan. It has no prime mover.


Ferrocarril del Pacifico Alco RSD12 502 at Nogales, Sonora, Mexico, April, 1984. Photographer: Craig Garver.

(Craig Garver, Public domain, https://www.flickr.com/photos/digitalrailartist/51703583048/)


ALCO RSD-12 Overview

Type and origin
Power type: Diesel-electric
Builders: American Locomotive Company / Montreal Locomotive Works
Model: RSD-12
Build date: April 1956 – March 1963
Total produced: 171
Configuration: AAR C-C
Gauge: 4 ft 8+1⁄2 in (1,435 mm) standard gauge
Prime mover: Alco 251B
Engine type: V12 Four-stroke diesel
Aspiration: Turbocharged
Cylinders: 12
Performance figures
Power output: 1,800 hp (1,300 kW)


Ferrocarril del Pacifico Alco RSD12 520 at Mazatlan, Sinaloa, Mexico, March 13, 1975. Photographer: Keith Ardinger. FCP bought 20 RSD12's in several orders. Only the last, FCP 518-520, were low hood. These three were always a treat when they came to Nogales, Sonora. (Craig Garver, Public domain, https://www.flickr.com/photos/digitalrailartist/51658894711/)


Ferrocarril del Pacifico Alco RSD12 510 at Guadalajara, Jalisco, December 24, 1964. Photographer: R W Biermann. (Craig Garver, Public domain, https://www.flickr.com/photos/digitalrailartist/50793756191/)