American Locomotive Company (Alco) used the word "Century" to brand its new line of 12 and 16-cylinder locomotives that were introduced in 1963. The marketing strategy was aimed at capitalizing on the "100" improvements and new features built into its 251C-driven series of four and six-axle freight haulers. The builder recognized that reliability, durability and fuel economy were at the forefront of railroad management concerns; and the Century series was a means of distancing the NY-based company from product woes of the past. Notched noses and "RS" identifiers were destined to become the domain of railfans and locomotive historians.

Interestingly, the first Century unit was not build at Alco's Schenectady, New York plant, but by the company's Canadian subsidiary, Montreal Locomotive Works. Completed in April 1963, the 2400-hp freight unit wore the maroon and gray of Canadian Pacific, along with road number 8300; not long afterwards the new C424 Alco (Specification DL640A) was re-numbered 4200. Erie- Lackawanna took delivery of the first Schenectady-built units (EL 2401-2403) in May of the same year.

At a length of 59'-4" (over coupler faces), the four-motor Century was offered in either a standard low-nose configuration or with an optional high-nose treatment (none of which were actually built). Total production of the model reached 190 units, with 92 produced at the subsidiary's assembly plant in Montreal.

A production roster, technical data sheet and ownership tracker have been provided for future reference.