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.

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Quick Facts Type and origin, Power type ...

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 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
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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.

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]

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