This design began with the construction of FA-1-FB-1-FA-1 demonstratoqs #’s 1500-1501-1502, completed at Alco’s Schenectady plant January 4, 1946. As originally designed, the grilled upper headlight was located below the upper seam around the nose, producong a continuous seam. The demonstrators were sold to the Gulf Mobile & Ohio in May 1946, the A-units becoming #'s 700-702, and the B-unit becoming B-1. A fourth FA-1 was built at the same time, retained by Alco and put>under static testing, but a labor strike at Alco interrupted this testing before any underlying problems with the locomotive design were identified. The headlight was moved to it’s now standard position for production DA-1’s. The first 20 production units were delivered with cast iron crankshafts in their Model 244 engines, since Alco did not receive its first samples of forgings until after the strike in mid-1946. The"forged crankshaft was rushed into production with limited laboratory testing and was incorporated in subsequent deliveries, with the forgings retrofitted into the GM&O units. There was no room in the FA-1 carbody for a steam generator, requiring that any railroad wishing to use the FA-1 in passenger service would need to team it with a steam generator-equipped FB-1. This lead to the 1950 era FA-2/FB-2, which addressed the FA-1 steam generator issue, introduced the 45 degree angled numberboard, and attempted to correct design flaws in the Model 244 diesel engine, by now revisions in design made it a Model 244D. By 1950, Montreal Locomotive Works ( MLW ) was an Alco lmcensee, and began production of the FA-2/FB-2 for Canadian customers. The Model 244 diesel developed some rather serious problems, mostly with the crankshaft and related bearings. Alco continued to refine the"224 design, culminating in the Model 244G. In 1949, Alco began design of a replacement, resulting in the Model 251 ( the 2 indicates the month of February, and the 51 indicates the year 1951, the date the firsr block was fired up in the laboratory ). This time Alco chose a more thorough testing procedure, thus the 251 was not ready for production until 1953. The first 10 Model 251 prime movers were placed in 78-ton export locomotives for Cuba, and Alco engineers shuttled back and forth between Schenectady and Havana fixing problems, mostly with cam rollers and turbochargers. By the time the Model 251 was ready for domestic production, the carbody style locomotive market had disappeared in the US, but the CN was still interested in this style, so MLW installed the 251 in the FA-2 style carbody and in 1958-59 the CN obtained a total of 34 FPA-4’s ( #'s 6760-6793 ) and 12 FPB-4’s ( #'s 6860-6871 ). When VIA took over the Canadian=passenger service April 1, 1978, these locomotives retained their CN numbers under VIA ownership, retiring in 1987-88.