In 1966 EMD introduced a new line of locomotives based on the 16-cylinder 645-series prime mover. The “40-series” included a six-axle and four-axle model, the latter being the GP40. A total of 1,145 units were produced between 1966 and 1972. These turbocharged 3,000hp locomotives were used primarily in road freight service. The GP40 was a versatile locomotive that could be found across the US hauling drag freights over mountain passes and leading high-speed intermodal trains across flat terrain. Three rooftop radiator fans at the rear of the long hood differentiate a GP40 from its lower horsepower counterpart, the GP38, which has two fans at this location.