ALCO S-1 and S-3

ALCO S-1 and S-3
Mid-Continent Railway No. 7, an S-1, rests between trains on October 10, 2004
Type and origin Power type Diesel Builder American Locomotive Company Montreal Locomotive Works Build date April 1940–June 1950 (S-1) February 1950–November 1953 (S-3) Total produced 543 (S-1) 300 (S-3)
Specifications Configuration: ​  • AAR B-B Gauge 4 ft 8+1⁄2 in (1,435 mm) standard gauge Trucks Blunt (S-1) AAR type A (S-3) Wheel diameter 40 in (1,016 mm) Minimum curve 50° (118.31 ft or 36.06 m) Wheelbase 30 ft (9.14 m) Length 45 ft (13.72 m) Width 10 ft 2+1⁄2 in (3.112 m) Height 14 ft 4+3⁄8 in (4.378 m) Loco weight 199,000 lb (90,000 kg) Fuel capacity 635 US gal (2,400 L; 529 imp gal) Prime mover ALCO 6-539T Engine type Four-stroke diesel Aspiration Natural Displacement 9,572 cu in (156.86 L) Generator GE GT 552-A Traction motors 4 × GE 731 Cylinders Straight 6 Cylinder size 12+1⁄2 in × 13 in (318 mm × 330 mm)
Performance figures Power output 660 hp (490 kW) Tractive effort 49,790 lb (22,580 kg)
Career Locale North America, Brazil, United Kingdom
[1][2]

The ALCO S-1 and S-3 were 660 horsepower (490 kW) diesel-electric switcher locomotives produced by ALCO and their Canadian subsidiary Montreal Locomotive Works (MLW). The two locomotives differed only in trucks, with the S-1 using ALCO's own Blunt trucks, and the S-3 using AAR type A switcher trucks. The S-1 was built between April 1940 and June 1950, with a total of 543 completed, while the S-3 was constructed between February 1950 and November 1953 (MLW until 1957) with total sales of 300. A modified version, the S-10, was built by MLW only; 13 were built between January and June 1958.

The S-1 and S-3 are distinguishable externally from the very similar S-2 and S-4 1,000 horsepower (750 kW) switchers in that they have a smaller exhaust stack with a round base and a smaller radiator shutter area on the nose sides. The S-1/S-3 radiator shutter area is taller than it is wide, while the S-2/S-4 radiator area is wider. The smaller stack is due to the lack of turbocharging.

The S-10 is not externally distinguishable from later Canadian-built S-3 locomotives; it differed mostly in electrical equipment.

The S-1 and S-3 models were sold to an extensive list of railroads and industrial operators, as detailed below. Major owners of the S-1 included the New York Central Railroad (NYC), with 71 locomotives; the New Haven with 65 locomotives; the L&N with 45 locomotives; the C&NW, with 29 locomotives; and the Pennsylvania Railroad (PRR) with 27 locomotives. Major customers for the S-3 included the CP, with 101; the CN, with 49; the NYC, with 43 locomotives; the B&M, with 16; and the PRR, with 13. The MLW S-10 was sold only to the CP.

The totals below include export orders and MLW-built locomotives.

ALCO constructed approximately 535 S-1s for the US market between 1940 and 1950.^[1][3]

ALCO and the Montreal Locomotive Works constructed approximately 300 S-3s for the North American market between 1950 and 1957.^[1][3]

MLW constructed 13 S-10s in 1958, all for the Canadian Pacific Railway, numbered 6601–6613.^[3] These units were essentially similar to late-built S3s, though with minor updates to the electrical gear.

In 1959, MLW built a final order of 660 horsepower switchers for the Canadian Pacific, as model S-11, numbered 6614–6623. The internal machinery of these units was essentially the same as that of the S-10, but the car body was radically redesigned, with the radiator on the front end of the hood instead of on the sides.^[4]

Numerous S-1 and S-3 locomotives remain in use, and several are preserved:

• Ex-U.S. Army S-1 No. 7372 is at the Western Pacific Railroad Museum and painted in Western Pacific colors.^[5]
• Ex-Canadian Pacific MLW S-3 No. 6568 is at the Saskatchewan Railway Museum.^[6]
• Two Ex-Steel Company of Wales S-1s are preserved and are being restored to working order at the Nene Valley Railway in England.
• Ex-Erie Railroad S-1 No. 307 is preserved at Riverside Park, Manhattan and painted in New York Central colors.^[7][8]
• Ex-Tennessee Central No. 51, later Cadiz Railroad No. 8, was on display in Trigg County, KY near exit 65 of Interstate 24. The unit is now currently in private ownership in nearby Christian County.^[9]
• Ex-New York Central No. 872, later Bath and Hammondsport No. 5, was acquired by the Rochester & Genesee Valley Railroad Museum in March 2025.^[10]
• Ex-South Omaha Terminal No. 1,^[11] later Hutchinson Northern Railroad No. 4, is owned by the Abilene and Smokey Valley Railroad. Number 4 was donated in 1993 and still runs excursions.^[12]

• List of ALCO diesel locomotives
• List of MLW diesel locomotives

Wikimedia Commons has media related to ALCO S-1 locomotives.

Wikimedia Commons has media related to ALCO S-3 locomotives.

• Alco/MLW S-1 Roster
• Alco/MLW S-3 Roster