thumb|[[Morristown & Erie C424 in May 2010]]
thumb|[[Delaware & Hudson C628 in August 1971]]
thumb|[[Reading Company C630 in May 1970]]
thumb|[[Chicago, Rock Island & Pacific Railroad C415]]
thumb|[[Delaware-Lackawanna Railroad C636 in August 2008]]
The ALCO Century Series locomotives were a line of road switcher locomotives produced by Alco, the Montreal Locomotive Works and AE Goodwin under license in Australia.
Production of the Century Series began in 1963 and ended in 1972. MLW and Goodwin continued to build Century locomotives after Alco ended locomotive production and shut down in early 1969. A total of 841 locomotives, in eleven variants, were produced over the ten years of production.
Background and development
During the 1950s, EMD had become the major player in the North American diesel locomotive market, with Alco relegated to second place. This was largely due to its 244 diesel engine suffering from significant reliability issues. In response to these issues a new engine design, the ALCO 251, was approved for development in 1951. This engine was put through nearly five years of testing before entering domestic production in four sizes (, , , and ) in a new line of locomotives.
By 1956 General Electric had launched its first Universal Series road locomotives primarily as export units. The U25B followed in 1961 and rapidly propelled GE into second place in the locomotive market, behind EMD.
Faced with this market situation, Alco in 1962 completely redesigned its road locomotive line, creating what would become the Century Series. The locomotives were designed to equal and surpass competitors' products in terms of both features and performance. To meet that end, the new locomotives included, among other features, a redesign of the air system, an improved traction control system, and improved accessibility and maintainability.
The series was first introduced on January 29, 1963, in Chicago, Illinois, consisting of three locomotives, the 2,000-horsepower B-B model C420, 2,400-horsepower B-B model C424, and the 2,400-horsepower C-C model C624, which was subsequently abandoned in favor of a more powerful model, the 2,750-horsepower C628. During speeches at the event, Alco executives promoted the new locomotives' reduced operating costs, a major effort in the design of the machines. Combined with unit reduction through higher powered locomotives, as well as liberal trade-in terms, Alco claimed operating cost could be reduced as much as 44%.
Production models
C420
The C420 was one of the first models launched, and was powered by a 2,000-horsepower, 12-cylinder, Model 251C engine. It was launched at the inaugural event for the Century series in 1963, and remained in production until 1968. A total of 131 units were built, including 22 passenger models for the Long Island Rail Road in 1963, supplemented in 1968 by an additional order of eight more with Alco's Hi-Ad trucks.
C424
The C424 was another of the initial models launched, and was powered by a 2,400-horsepower, 16-cylinder, Model 251B engine. It remained in production until 1967. A total of 190 units were built, although only 53 went to domestic customers; the remainder went to Mexican or Canadian customers.
C425
The C425 was launched in 1964 in response to a request from Erie-Lackawanna for a 2,500-horsepower B-B locomotive, and was powered by a 2,500-horsepower, 16-cylinder Model 251C engine. It remained in production until December 1966, just five months before the final C424 was delivered in May 1967. A total of 91 units were built. Ultimately, poor performance led to their retirement after less than eight years in service.
C630
The C630 was launched in 1965, prompted by the impending launches of locomotives by both GE and EMD of equivalent size, and was the first production locomotive to use AC technology, as DC generators were too large and complex to be used at such high powers. It was powered by a 3,000-horsepower, 16-cylinder, Model 251E engine. It was launched in 1965, and remained in production until 1967, with 77 units produced.