The GP40 is a 4-axle diesel-electric road-switcher locomotive built by General Motors, Electro-Motive Division between November 1965 and December 1971. It has an EMD 645E3 16-cylinder engine generating 3,000 hp (2,240 kW).
The GP40 is 3 feet (0.914 m) longer than its EMD 567D3A-engined predecessor, the GP35, and distinguished visually by its three 48-inch radiator fans at the rear of the long hood, while the GP35 has two large fans and a smaller one in between. It was built on a 55 ft (16.76 m) frame; the GP35 was built on a 52 ft (15.85 m) frame - as was the GP7, 9, 18, and 30. The difference in length can be seen in the GP40's ten handrail stanchions compared to the GP35's nine.
1,187 GP40s were built for 28 U.S. railroads; 16 were built for one Canadian carrier, Canadian National; and 18 were built for two Mexican carriers, Ferrocarril Chihuahua al Pacifico and Ferrocarriles Nacional de Mexico. 60 units were built with high-short-hoods and dual control stands for Norfolk & Western Railway. Two passenger versions, the GP40P and GP40TC, were also built, but on longer frames to accommodate steam generators and HEP equipment.
On January 1, 1972, the GP40 was discontinued and replaced by the GP40-2, which has a modular electrical system and a few minor exterior changes.