The F7 was the fourth model in GM-EMD's successful line of F-unit locomotives, and by far the best-selling cab unit of all time. In fact, more F7s were built than all other F-units combined.
The F7 succeeded the F3 model in GM-EMD's F-unit series, and was replaced in turn by the F9. Final assembly was at GM-EMD's La Grange, Illinois, plant or EMD's London, Ontario, facility. There was no F4, -5 or -6 model; "7" was chosen to match the contemporary twin-engine E7, and was also applied to the new GP7 road-switcher.
The F7 differed from the F3 primarily in internal equipment—mostly electrical—and some external features. Its continuous tractive effort
rating was 20 percent higher, e.g. 40,000 lbf (180 kN) for an F7 with
65 mph (105 km/h) gearing, compared to 32,500 lbf (145 kN) for an F3
with the same gearing.
Many F7s remained in service for decades, as railroads found them
economical to operate and maintain. However, the locomotive was not
very popular with yard crews who operated them in switching service
because they were difficult to mount and dismount, and it was also
nearly impossible for the engineer to see hand signals from a ground
crew without leaning way outside the window. As most of these engines
were bought and operated before two-way radio became standard on most
American railroads, this was a major point of contention. In later
years, with the advent of the "road switchers" such as the EMD GP7, F-units were primarily used in "through freight" and "unit train" service where there was little or no switching to be done.
The NYC had 230 A units and 54 B units.