ALCO S-1 and S-3
The ALCO S-1 and S-3 were 660 horsepower (490 kW) switcher diesel-electric locomotives produced by ALCO and their Canadian subsidiary Montreal Locomotive Works (MLW). Basically, the two locomotives differed only in trucks, with the S-1 using ALCO's own Blunt trucks, and the S-3 riding on standard 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.
Identification
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.