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In the 1920s, many railroads in the United States had retired 0-4-0 steam locomotives because they were too small for switching duties. This was not the case on the Pennsylvania Railroad (PRR). The PRR was keen on this wheel arrangement due to complex street and tight industrial trackage across its broad network. For some of these lines, the railroad needed a large 0-4-0 to handle the larger switching activities the railroad had. Although the class B was designated for steam locomotives with the 0-6-0 wheel arrangement, these steam locomotives could not fit the tight and complex street, dockyard and industrial trackage the railroad had in its possession.
As early as 1948, the A5s steam locomotives started to be replaced by higher horse powered and heavy duty diesel switchers. Over the next year, these switchers were gradually replaced by diesel locomotives. Finally in 1957, the Pennsylvania Railroad converted from steam to diesel power and the last of the class was withdrawn.
Staufer, Alvin F.; Pennypacker, Bert (1962). Pennsy Power: Steam and Electric Locomotives of the Pennsylvania Railroad, 1900-1957. Research by Martin Flattley. Carollton, Ohio: Alvin F. Staufer. ISBN978-0-9445-1304-0.