The Alco S-2 is a diesel-electric locomotive built by the American Locomotive Company (ALCO) from 1940 to 1950. It features a 1,000 horsepower engine and is primarily used for switching and short-haul freight operations. The S-2 is known for its distinctive design, which includes a low hood and a short wheelbase, making it highly maneuverable in rail yards. With over 1,000 units produced, the Alco S-2 became popular among various railroads in the United States and Canada. Its reliability and efficiency contributed to the transition from steam to diesel power in the rail industry, influencing the design of future locomotives like the Alco S-4.