The F-7 was the zenith of the "covered wagon," or carbody-style diesel. With 3,849 units built between 1949 and 1953, the F-7 was both the most popular carbody diesel and its last hurrah. By 1954 U.S. railroads had virtually stopped ordering F-units in favor of hood units like EMD's GP9 and Alco's RS-3. The side walkways of hood units offered better access for maintenance and better visibility for backup moves, making them truly universal locomotives useful for both mainline runs and road switching.
The F-unit, however, was, in Trains magazine editor David P. Morgan's words, "the diesel that did it" - retired the steam engine and changed railroading forever. The F-unit and its contemporaries were also the first standardized locomotive designs bought by American railroads since USRA steam engines. Whereas the steam engines of most railroads had a distinctive and easily-recognized "look," F-units were the same everywhere. But they had one great visual advantage over steam: their flat sides were like rolling billboards. Artists at EMD and the railroads responded with distinctive color schemes and, for the first time since the late 1800's, American locomotives became a riot of color in the postwar era.
Externally, the F-7 was very similar to the earlier F-3. The key spotting features that distinguished an F-7 were its stainless steel upper body grilles that replaced the "chicken wire" worn by most F-3s, and the rooftop dynamic brake fan that replaced the F-3's rectangular roof vents just behind the cab. Internally, the F-7 was also an evolution of the F-3. While horsepower was the same, new D27 traction motors allowed the F-7 to handle a heavier load.
Add this B-Unit to your AA or single A unit locomotives for a more prototypical consist.