Here is a summary of the first members of the 600-, 900-, 1200-, 1350-, 1500-, and 1800-horsepower series of EMD locomotives, mostly from Marre’s book:
600 horsepower: SC (1935-1939); SW('36-39)
900 horsepower: NC (37-38); NC1 (37); NC2 (37); NW (37-38); NW1 (37-38); NW1A (38); NW4 (38)
1200 horsepower: TA (37)
1350 horsepower: FTA, FTB (39-45); F2A, F2B (46)
1500 horsepower: F3A, F3B (45-49); F7A, F7B (49-53); FP7 (49-53)
1800 horsepower: EA, EB (37-38); E1A, E1B (37-38); E2A, E2B (37)
I see a pattern.
Marre also cited:
1750 hp F9, FP9
1800 hp FL9
But if EMDs website says F means freight, I’m not gonna correct’em.
Have a great weekend!
F did stand for freight ,the f on the car body indicated the front end of diesel locomotives.The FP-7 was stretched for greater water and fuel capacity, A units only,B units had room for larger tanks. Alco cabs wereFA for freight and PA for passenger service. S stood for six hundred horse power,N for nine hundred horsepower & T was for transfer engines. The TA was a four axle passenger diesel. W as in SW-1500 meant welded frame. Hope this helps.