The Century 424 was a four-axle, 2,400 hp diesel-electric locomotive of the road switcher type. 190 examples of this locomotive were built between April 1963 and May 1967. Cataloged as a part of Alco's Century line of locomotives, the C424 was intended to replace the earlier RS-27 model and offered as a lower-priced alternative to the C425. Montreal Locomotive Works also built this locomotive as MLW Century 424.
The ALCO Century 425 was a four-axle, 2,500 hp diesel-electric road switcher locomotve. 91 examples of this locomotive were built between October 1964 and December 1966. Cataloged as part of ALCO's "Century" line of locomotives, the C425 was an upgraded version of the C424. The C425 employed the same main generator found in General Electric's U25B model.