In 1939 General Motors Electro - Motive Division issued a challenge to the supremacy of steam traction with the introduction of the FT class.
Although proven as capable traction for passenger traffic, many were sceptical of the ability of diesels to haul freight. GM launched an 11 month tour of 35 states and 20 Class 1 railroads demonstrating the advantages of modern traction.
The FT class (F for freight T for 2700 hp with b-unit) proved a capable machine, hauling more freight, using less fuel and requiring less maintenance than any steam locomotive. Several units could be combined to meet horsepower requirements; this ability to 'lash' several units together, meant that a single crew could operate them using 'multiple unit' controls.
Originally designed for freight, F-units were widely used on passenger services, many being fitted with boilers for passenger car heating.
Over 7600 A & B units were built between 1939-1960 ending with the FL9, making them the top selling cab unit of all time. The F unit inspired a more colourful era in the history of railroads, as several operators adourned the art deco carbodies with flamboyant liveries such as the famous Santa Fe 'warbonnet' scheme.