ALCO S-2 and S-4
 The ALCO S2 and S4 were 1000 horsepower (746 kW) switcher diesel-electric locomotives produced by ALCO and Canadian licensee Montreal Locomotive Works (MLW). Basically the two locomotives differed only in trucks with the S-2 using ALCO's own Blunt trucks and the S-4 riding on standard AAR type A switcher trucks. Both were powered by ALCO 539 turbocharged 6-cylinder diesels.