The ALCO Century 420 is a four-axle, 2,000 horsepower (1,491 kW) diesel-electric locomotive.

131 were built between June 1963 and August 1968.

Cataloged as a part of ALCO's "Century" line of locomotives, the C420 was intended to replace the earlier RS-32 model.

All units ordered by Mississippi Export, New York, Chicago & St. Louis Railroad ("Nickel Plate"), and Piedmont & Northern Railway have been scrapped.

This diesel locomotive-related article is a stub.