The FA cab unit locomotive series was introduced in the late 1940s under a partnership from the American Locomotive Company and General Electric. At the height of cab units, this was ALCOs foray into the market. The F designation meant their design and usage would be best suited for freight, although the FA and matching FB booster unit could be seen in service almost anywhere. Over 600 were built from 1946 to 1956 with 400 of them being FA units. Many of these saw service after being sold from their original purchaser.