The Alco S-1 is a diesel-electric locomotive built by the American Locomotive Company (ALCO) from 1940 to 1949. It features a 1,000 horsepower engine and is primarily used for switching and light freight duties. The S-1 was designed for short-haul operations and is known for its reliability and versatility in various rail environments. With a total production of around 600 units, the S-1 was popular among many railroads in the United States. Its compact size and powerful performance made it suitable for industrial and yard service. The locomotive is part of the broader category of diesel locomotives, which revolutionized rail transport in the mid-20th century.