Alco "S-2" Locomotives

Last revised: March 8, 2023

By: Adam Burns

The Alco S2 was the second model of switcher the company produced although it was constructed at the same time as the earlier S1.

One of the significant differences between the two models was the increased horsepower of the S2, which was a 40% increase over the previous design.

The model had a ten year production run and railroads apparently liked the increased power as the S2 went on to being Alco's best selling small switcher.

While the large Class I systems tended to purchase the most S2s numerous smaller lines and industries also found the locomotive quite useful. 

Typical of this era, American Locomotive produced a very rugged and reliable design, utilizing its 539T prime mover, that numerous railroads and other companies found quite useful.

Today, the S2 is one of the most preserved Alco models in existence and can be found throughout the country many of which are still operational.

Additionally, a handful of these locomotives still find a place on shortline rosters who find the units easy to maintain, rugged, with a knack to pull just about anything.


San Francisco Belt Railroad S2 #23 runs light along the waterfront in April of 1977. Author's collection.


Like its S1 sister, the Alco S2 was first produced in 1940 featuring an end-cab design using McIntosh & Seymore's 539 diesel engine. However, unlike the S1 the S2 was more powerful and came equipped with a 1,000 horsepower rating.

With this increased power the S2 was more suitable for a wide range of duties from yard and switching services to freight operations (normally on branch and secondary lines).

The adept little switcher and its ability to seriously pull (an Alco trademark with all of its diesels) made it a favorite amongst industries as well because it could lug around heavy cuts of cars while also being able to negotiate the sharp curves and tight clearances found in these settings.

Missouri Pacific S-2 #1048 (built as #9130) lays over in New Orleans, Louisiana, circa 1965. collection.

The Alco S2, like the S1, was born out of the company's long history (even by 1940) of studying and developing small diesel locomotives that dated back to 1918.

Their first true diesel line began with a series of switchers produced in 1931. These locomotives were developed in conjunction with McIntosh & Seymore and Westinghouse, the former providing the prime mover and the latter air components and a revolutionary cab design (the "Visibility Cab") that enabled crews maximum visibility.

With the help of famed industrial designer Otto Kuhler, Alco gave the models a clean look with beveled edges to the hood and cab.  They were offered in horsepower ratings of 300, 600, 660, 900, and 1000.

Erie Lackawanna S2 #531 (built as Delaware & Hudson #3016 and acquired in 1955) is seen here at work in Binghamton, New York during November of 1966. Author's collection.

Contrary to popular belief in the railfan community, Alco never gave its initial line of switchers any name since the builder only had this single series in production, as John Kirkland notes in his book, "The Diesel Builders: Volume Two."

After Alco cataloged a low-hood variant (the "S" series), railfan publications sought to differentiate its first switchers.  As a result, the term "High Hood" was coined.

Erie Lackawanna S2 #531 (ex-Erie #531) and #541 (ex-Lackawanna #482) are at work at the Delaware & Hudson interchange in Binghamton, New York in February, 1966. Author's collection.

When Alco released the S series in 1940 it carried over many of the Kuhler design recommendations. As mentioned above the builder also carried over the McIntosh & Seymour prime mover and also continued to work with General Electric (provided traction motors and generators) and Westinghouse (provided air components such as brakes and compressors).

Easily the most popular design of the S series the S2 sold more than 1,500 units to various Class Is, short lines, and industries by the time production had ended in June, 1950.

Of note, the company's Montreal Locomotive Works branch also sold a number of S2s. Several Canadian lines including the Canadian National, Canadian Pacific, Alma & Janquiere, Ontario Northland as well as industry Aluminum Company of Canada all purchased the MLW version of the S2.

Data Sheet and Specifications

Entered Production9/6/1940 (Elgin, Joliet & Eastern #451)
Years Produced9/6/1940-6/29/1950
Model SpecificationE1540
Engine539T, 6-Cylinder In-Line
Carbody StylingAlco
Length (Between Coupler Pulling Faces)45' 5.75"
Height Above Rail Head14' 6"
Weight230,000 Lbs.
Truck TypeBlunt
Truck Wheelbase8'
Wheel Size40"
Traction MotorsGE 731 (4)
Traction GeneratorGT553
Gear Ratio75:16
Tractive Effort Rating34,000 Lbs. at 8 MPH.
Top Speed60 MPH

Production Rosters


Owner Road Number(s) Quantity Date Built
Akron, Canton & Youngstown10111942
AlcoExperimental (No Road Number)11942
Alton Railroad10-24151944-1945
Angelina & Neches River Railroad10011949
Atlanta & St. Andrews Bay1001-100221942
Atlantic Coast Line602, 604, 610-614 (Evens), 618-622 (Evens), 624-634 (Evens), 636-642 (Evens)181942-1944
Baltimore & Ohio475-533591943-1948
Bauxite & Northern Railway911948
Bingham & Garfield Railway80011942
Boston & Maine1260-126561944-1945
Buffalo Creek Railroad44-4741947-1948
Carnegie-Illinois Steel Corporation70-7341946
Central Of Georgia21-35151940-1948
Central Railroad Of New Jersey (CNJ)1067-107151944
Central Vermont Railway7918-791921942
Chattahoochee Valley Railway10011946
Chesapeake & Ohio5000-5057581949-1950
Chestnut Ridge Railway10-1121946
Chicago & North Western1003-1015, 1025-1035, 1083-1092341942-1950
Chicago Great Western8-1031947
Chicago, St. Paul, Minneapolis & Omaha (C&NW)90-9341940-1944
Chicago, West Pullman & Southern40-4121944-1949
Cincinnati, New Orleans & Texas Pacific (Southern)6057-605931941
Delaware & Hudson3000-3032331944-1949
Delray Connecting6411945
Denver & Rio Grande Western101-119191941-1944
Donora Southern Railroad511949
Elgin, Joliet & Eastern451-462121940-1948
Erie Railroad500-525261946-1949
Fairport, Painesville & Eastern Railroad101-10441945-1947
Fonda, Johnstown & Gloversville20-2121945-1946
Galveston, Houston & Henderson Railroad20-2121949
General Electric411949
Grand Trunk Western7915-7935211941-1946
Great Northern1-10101950
Gulf, Mobile & Ohio1001-1012121941-1946
Houston Belt & Terminal11-1991943-1948
Illinois Terminal700-711121948-1950
International-Great Northern Railroad (MP)9156-9159, 9168-916961945-1949
Kaiser Steel Corporation1008-100921945-1949
Kewaunee, Green Bay & Western20111949
Kansas City Terminal51-5991940-1949
Lehigh & New England611-61661948-1949
Lehigh Valley150-165161942-1949
Long Island Rail Road446-449, 451-460141948-1949
Longview, Portland & Northern Railway110-11121946-1949
Los Angeles Junction Railway1-551941-1949
Louisville & Nashville2200-2201, 2220-222471943-1949
Maine Central301-30331949
Manufacturers Railway (St. Louis)204-21181940-1948
Massena Terminal Railroad1011948
McKeesport Connecting1001-100771948
Michigan Limestone & Chemical Company107-11481941-1946
Milwaukee Road1657-1669, 1672-1679, 1850-1862341940-1950
Minneapolis & St. Louis10211941
Minnesota Transfer93-9421946
Missouri Pacific9107-9116, 9128-9132151941-1949
Monongahela Connecting144-149, 151-159151946-1949
Nashville, Chattanooga & St. Louis5-1171942-1946
Newburgh & South Shore Railroad8, 11-12, 13A-17A81941-1946
New Haven0600-0621221943-1944
New Jersey Zinc Company20-2231945-1946
New York, Susquehanna & Western202-206, 20861942
New York Central8500-8536, 8550-8589771943-1950
Nickel Plate Road1-6, 25-45271942-1950
Northeast Oklahoma Railroad703-70421946-1947
Northern Pacific107-108, 113-118, 150-152, 711-712131941-1949
Northern Pacific Terminal35-4171943-1950
Oliver Iron Mining Company916-917, 920-921, 926-92761942-1944
Patapsco & Back Rivers Railroad226-22721947
Pennsylvania5641-5660, 5926-5931, 9105-9109, 9204, 9278-9287421948-1950
Peoria & Pekin Union300-30121941-1942
Philadelphia, Bethlehem & New England26111945
Pittsburgh & Lake Erie (NYC)8537-8549131948-1949
Port Huron & Detroit6011949
Portland Terminal (Maine)1051-105441941-1948
Richmond, Fredericksburg & Potomac1, 51-71221942-1948
Rock Island716-729141942-1948
Santa Fe2322-2391701942-1949
St. Louis-San Francisco (Frisco)290-29451948-1949
Seaboard Air Line1403-1405, 1425-1434131942-1948
Solvay Process Company411946
South Buffalo Railway71-77, 81-91181940-1950
Southern Pacific1300-1309, 1330-1361, 1362-1363 (1st/2nd), 1364-1370, 1386-1392, 1426-1441761941-1950
Spokane, Portland & Seattle20-2891940-1943
State Belt Railroad Of California20-2561943-1945
Tennessee Coal & Iron500-505, 55071941-1947
Terminal Railway Alabama State Docks451-452, 49131945-1949
Terminal Railroad Association of St. Louis569-590221941-1949
Texas & New Orleans (SP)30-71, 89-94481943-1950
Texas Gulf Sulphur Company5-621947-1949
Texas Pacific-Missouri Pacific Terminal11-1441948
Toledo Terminal101-10881946-1949
Truax-Traer Coal Company10111948
Union Railroad505-535311941-1948
Union Pacific1036-1054, 1119-1153541943-1945
U.S. Army7100-7125, 7450, 7465281942-1943
U.S. Navy65-00029, 65-00030, 65-00040 (4), 65-00041, 65-00076, 65-00077, 65-00086, 65-00087, 1291943-1944
Weirton Steel201-20991945-1949
Western Maryland125-127, 140-14481943-1946
Western Pacific551-562121943-1950
Wheeling Steel20011943
Wisconsin Central (Soo)2103-211081942-1949
Youngstown & Northern Railroad213-216, 219-22281940-1949
Youngstown Sheet & Tube Company1001-100221947

Montreal Locomotive Works

Owner Road Number(s) Construction Number(s) Completion Date
Canadian Pacific7076, 707875852-7585311/1948
Canadian Pacific7079-709575854-7587012/1948-3/1949
Canadian National7975758713/1949
Canadian Pacific707776429*5/1948
Canadian National7976-799476450-764683/1949-6/1949

* Built at Alco's Schenectady, New York plant.


  • 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.

Spokane, Portland & Seattle S2 #24 lays over in Spokane, Washington on May 2, 1965. Fred Byerly photo. collection.

In total, MLW built 114 examples of the model for these companies. The S2 was also the last in the S series to be equipped with Alco's Blunt trucks, as all future designs used the more standard AAR type 1 or type 2 trucks.

The S2 also offered some serious tractive effort, another reason it sold very well. For weighing only about 115 tons the locomotive could produce 69,000 pounds of starting tractive effort and around 30,000 pounds continuous. 

The S2 was the same length as the S1 and one of the few noticeable differences was the size of the radiator grill, which was smaller on the S1, as well as the smoke stack (the S2 featured a flared stack at its bottom while the S1's stack was more conical). These were not all of the slight design differences of the two but some of the more noticeable.  

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