ALCO S-1 and S-3

The ALCO S-1 and S-3 were 660 horsepower diesel-electric switcher locomotives produced by ALCO and its Canadian subsidiary Montreal Locomotive Works. The two differed only in trucks, the S-1 using ALCO Blunt trucks and the S-3 using AAR type A switcher trucks. The S-1 was built from April 1940 to June 1950, with 543 completed, and the S-3 from February 1950 to November 1953 at ALCO, with Montreal building them until 1957, for sales of 300. A modified S-10 followed from Montreal in 1958 for the Canadian Pacific. They are told apart from the 1,000 horsepower S-2 and S-4 by a smaller exhaust stack, because they lack turbocharging. Numerous units remain in use and several are preserved.