The EMD F-series designated several types of four-axle diesel-electric freight locomotives of which more than 7,500 were built between 1939 and 1960. They came after the A1A-A1A E-series passenger locomotives, where the E stood for “eighteen hundred”, designating the total installed horsepower. With the 16-cylinder variant of the 567-series engine initially delivering 1,350 hp, the new locomotive series got the letter F for “fourteen hundred”.

As the initial model was usually marketed as a twin set consisting of an “A” cab unit and a “B” booster unit, it was called FT with the T for “Twin”. The first locomotives built for a customer were delivered to the ATSF in December 1940. They were the first diesel-electric locomotives equipped with a dynamic brake since the customer insisted on that. The FT was not only used as A-B set, but also as a A-B-B-A set delivering 5,400 hp or even as an A-B-A set.

The FT is mostly been seen as the locomotive that proved that diesel traction was the future of freight service. Since the War Production Board limited the construction of diesel locomotives for civil usage, EMD was lucky since they did not produce steam locomotives as an alternative. So they could quickly win the market lead and establish the widest customer base for the time after the war when other manufacturers could resume production of diesel locomotives without restrictions. When production of the FT ended in November 1945, 555 A units and 541 B units had been completed.

The next variant was the F2 that did not have many differences compared to the FT. Only 74 A units and 30 B units were built. The biggest numbers were produced of the F3 and F7 which had the “B” variant of the 567 engine that delivered 1,500 hp. Of the F3, 1,106 A units and 694 B units were built between 1945 and 1949. The F7 even reached higher numbers with 2,393 A units and 1,463 B units between 1949 and 1953. Additionally, 381 of the FP7 were built, what was a dedicated passenger variant that was four feet longer due to its steam heating boiler.

The last iteration of the F series was the F9 that produced 1,750 hp with the 567C engine. Although production ran until 1960, only 101 A units and 156 B units could be sold. This can be explained with the fact that the road switchers of the GP series already established themselves since the beginning of the fifties. There was also an FP9, but only 90 of this could be sold.