Alco "S-4" Locomotives

Last revised: April 28, 2023

By: Adam Burns

The Alco S4 was the fourth model of switcher series the company produced and debuted a decade after the S1 and S2 designs in 1949. The American Locomotive Company (Alco) began production on the S4 directly after the S2 in June, 1950.

It was quite apparent that railroads preferred Alco's more powerful small switchers as both the S2 and S4 far outsold both the S1 and S3 by more than 1,400 units!

While not quite as popular as the S2, the S4 still sold nearly 800 examples and could likewise by found on railroads and within industrial settings all around the country.

Alco's Montreal Locomotive Works branch (located in Montreal, Quebec) also saw a large number of orders from Canadian lines.

Today, the S4 is one of the best preserved examples of Alco diesel locomotives as more than a dozen are either preserved or in operation on numerous museums and tourist lines around the country.


2860203952734623742756789420893509789.jpgSt. Louis-San Francisco Railway (Frisco) S4 #298 carries out switching chores in Miami, Oklahoma, circa 1970. This unit was built as Northeast Oklahoma Railroad #706. Mac Owen photo. collection.


The Alco S4 design began production in June, 1950 (Schenectady) as soon as the last S2 had rolled off of the assembling line. The model is only slightly different from its earlier S2 sibling with minor carbody variations such as a relocation of the bell from behind the exhaust stack to the front of the hood (unless otherwise requested).

Otherwise, externally both models could hardly be distinguished from the other. Internally, both designs featured four axles and traction motors and air components from General Electric and Westinghouse.

They also both used McIntosh & Seymour's model 539 prime mover that could produce 1,000 horsepower and featured turbocharging.  Finally, each model weighed in at just under 115 tons.

20350923572374275786893893907489.jpgPennsylvania S4 #8434 was photographed here in Detroit, Michigan between assignments, circa 1964. Fred Byerly photo. collection.

There were more striking differences, though. The S4 came equipped with updated type A AAR trucks whereas the S2 had used Alco's very own Blunt trucks (one of the only manufacturers to design its own trucks).

Additionally, the S4 offered much more tractive effort (a big advantage in the world of switching and shuffling cars); 72,400 pounds starting and 34,000 pounds continuous compared to the S2's 69,000 pounds starting and 29,200 continuous.

Interestingly, while few Canadian or foreign  lines purchased early models of Alco's Switcher class (the S1 and S2) many bough examples of later designs like the S3 and S4.

The S4 also attracted many more industries due to the fact that it featured increased horsepower and tractive effort but retained the same size and dimensions of earlier models (making it agile and maneuverable in the tight spaces of such settings).

Morristown & Erie S4 #14, the road's only example, carries out switching work at Roseland, New Jersey, circa 1960. Meyer Pearlman photo. collection.

Following the Alco S4 the company had a difficult time selling switchers, which was partly due to the fact that railroads began to find that road switchers could perform the tasks of switching and shuffling cars just as well, and could also be used in regular freight service.

While the specialized needs of a switcher diminished to some extent by the 1960s, when Alco completed production of the S4 in 1960 it had sold some 782 units in total.

Data Sheet and Specifications

Entered Production (Alco)8/3/1950 (Maine Central #311-312)
Entered Production (MLW)6/1949 (Canadian Pacific #7099)
Years Produced (Alco)8/3/1950-1960 (Armco Steel Corporation E116)
Years Produced (MLW)6/1949-1/1957 (Canadian National #8195)
Model SpecificationE1540A/B
Engine539T, 6-Cylinder In-Line
Carbody StylingAlco
Length (Between Coupler Pulling Faces)45' 5.75"
Height Above Rail Head14' 6"
Weight230,000 Lbs.
Truck TypeGRS Rigid Bolster, Drop-Side Equalizer (AAR Type-A)
Truck Wheelbase8'
Wheel Size40"
Traction MotorsGE 731 (4)
Traction GeneratorGT563
Gear Ratio75:16
Tractive Effort Rating34,000 Lbs. at 8 MPH.
Top Speed60 MPH

The primary difference between E1540A and E1540B was the switch from short to long-shank couplers.  The transition occurred in Schenectady in 1954:

  • Piedmont & Northern #1005 (construction number 81094) was the final to receive short-shank couplers and completed on April 27, 1954.

  • Armco Steel #E111 (construction number 81095) was the first to receive long-shank couplers, completed on April 30, 1954.

At the Montreal Locomotive Works the change took place between 1954 and 1955:

  • Canadian National #8033 (construction number 76448) was the final to receive short-shank couplers, completed on March 10, 1954.

  • Falconbridge Nickel Mines #108 (construction number 76449) was the first to receive long-shank couplers, completed on July 15, 1955.
384602395273572698378483900983.jpgMilwaukee Road S4 #818 (built as #1895) was photographed here at Kansas City, Missouri in December of 1968. Fred Byerly photo. collection.

Production Roster


Owner Road Number(s) Quantity Date Built
Algiers, Winslow & Western Railway1-221953
Angelina & Neches River1211958
Armco Steel CorporationE111-E114, E11651954-1960
Baltimore & Ohio468-474, 534-545, 9078-9114561953-1957
Bessemer & Lake Erie291-29221952
Central Vermont Railway8015, 8027, 8080-808141951-1955
Chesapeake & Ohio5100-5113141953
Chicago & North Western1077-1079, 1093-1099101951-1955
Chicago, St. Paul, Minneapolis & Omaha (C&NW)10111952
Cincinnati, New Orleans & Texas Pacific (Southern)6074-607521951
Delaware & Hudson3033-3050281950
Erie Railroad526-52941951-1952
Fairport, Painesville & Eastern10511951
Ford Motor Company10008-1001251954
Genesee & Wyoming3511959
Georgia Port Authority10111952
Grafton & Upton100111952
Grand Trunk Western8026, 8034-8035, 8082-8090, 8196-8205221953-1956
Hammond Lumber Company10111950
Houston Belt & Terminal20-2121951
Ideal Cement Company5511955
Illinois Northern29-3461950-1951
Kaiser Steel Corporation1011-1013, 1015-101981951-1957
Lehigh Valley166-16721951
Longview, Portland & Northern11211951
Los Angeles Junction Railway6-721950-1953
Louisville & Nashville2225-2232, 2350-2369281951-1953
Maine Central311-31771950-1954
Manufacturers Railway (St. Louis)21211951
Massena Terminal1111951
Michigan Limestone & Chemical Company11511950
Milwaukee Road1863-1896341950-1954
Minnesota Transfer100-10561951
Monongahela Connecting139-14351951
Morristown & Erie1411952
National Lead Company911954
New Jersey Zinc Company2311953
New York Central8590-8632431952
Nickel Plate Road46-61, 65-83351951-1953
Northeast Oklahoma Railroad705-70621950-1952
Northern Pacific713-724121951-1953
Northern Pacific Terminal42-4541952-1954
Pennsylvania8430-8434, 8487-8499, 8886-8901341950-1954
Piedmont & Northern1000-100561954
Pittsburgh & Lake Erie (NYC)8633-8667351950-1953
Portland Terminal (Maine)1055-105841950
Santa Fe1500-1537381952-1953
Schafer Brothers Logging Company2011950
Seaboard Air Line1482-1491101953
South Buffalo Railway92-9981951-1952
Southern Pacific1464-1485, 1514-1528, 1551-1567441951-1955
Tennessee Copper Company10611953
Terminal Railway Alabama State Docks511, 521, 541, 57141951-1957
Texas & New Orleans (SP)95-104101951
Texas & Northern10-1121951
Texas City Terminal3311953
Toledo Terminal109-11131951-1952
Union Pacific1154-1198451955-1956
Union Railroad536-53721951
U.S. Steel111955
Wabash Railroad322-32431953
Weirton Steel210-21451951-1959
Western Maryland145-14621951
Western Pacific563-56421951
Wisconsin Central (Soo)211611952
Youngstown & Northern222-22321950-1951

Montreal Locomotive Works

Owner Road Number(s) Construction Number(s) Completion Date
Canadian National8028-803376443-764481/1954-3/1954
Falconbridge Nickel Mines108764497/1955
Canadian Pacific7099-710876469-764786/1949-7/1949
Alma & Jonquieres101764798/1949
Allard Lake Mines1764808/1949
Canadian National7995-800576481-764918/1949-10/1949
Allard Lake Mines2764929/1949
Canadian National8006-800776493-7649410/1949
Asbestos & Danville46764958/1949-10/1949
Canadian National8008-801176496-7649910/1949-11/1949
Canadian Pacific7115-711877290-772933/1953-5/1953
Asbestos & Danville48772944/1953
Canadian National8012-801477581-7758312/1949-1/1950
Canadian Commercial Corporation1775841/1950
Abitibi Power & Paper80775856/1950
Ontario Northland12037758610/1950
Asbestos & Danville477758711/1950
Quebec Iron & Titanium4775886/1951
Alma & Jonquieres102775897/1952
Canadian Pacific7109-711377590-775947/1952-8/1952
Canadian Pacific71147759512/1951
Canadian National8016-802577596-7760512/1951-11/1952
Canadian National8036*791938/1955
Canadian National8037-803879194-791959/1955
Canadian National8039-815081217-812289/1955-11/1955
Canadian National8078-807981229-8123011/1955
Canadian National8051-807781231-8125712/1955-2/1956
Asbestos & Danville49812588/1956
Canadian National8163-817081259-812668/1956-9/1956
Canadian National8171-818081549-815589/1956-10/1956
Canadian National8181-819081573-8158210/1956-12/1956
Canadian National8191-819581653-8165712/1956-1/1957

* First MLW-built S4 with long-shank couplers.


  • Foster, Gerald. A Field Guide To Trains. New York: Houghton Mifflin, 1996.
  • Kirkland, John F. Diesel Builders, The:  Volume Two, American Locomotive Company And Montreal Locomotive Works. Glendale: Interurban Press, 1989.
  • Pinkepank, Jerry A. Diesel Spotter's Guide.  Milwaukee: Kalmbach Publishing Company, 1967.
  • Solomon, Brian. Alco Locomotives. Minneapolis: Voyageur Press, 2009.

Penn Central S4 #9832 (built as Pennsylvania #8432). Location not recorded. September, 1969. collection.

The Canadian lines including the Canadian Pacific, Canadian National, Ontario Northland, Asbestos & Danville, Alma & Janquiere and industries Abitibi Power & Paper, Falconbridge Nickel Mines, and Quebec Iron & Titanium picked up some 145 S4s through Alco's Montreal Locomotive Works.

The CN would come to own the most of these buying 113 units.  Interestingly, after the S4 Alco would sell less than 200 examples of its final three switcher designs including the special order S5, S6, and transfer model T6.  

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