central cab, raised higher, with narrower-topped, streamlined "noses" to the locomotive to enable the crew to see forward. The final 28 locomotives were built to this design, which was not given a separate class designation since it was mechanically and electrically identical; they were called class P5a (modified), and colloquially Modifieds. Documentation published in 2010 disproved the decades long belief that the modified P5's new shell design came first and was then applied to the GG1, R1, and eventually the DD2. Instead, it was revealed that the GG1 project, under the direction of industrial designer Donald R. Dohner, was the first to receive the center cab design, and that soon afterward it was applied to the R1 and P5. The Modified units (along with the R1 and prototype GG1) were built with riveted carbodies. However, unit #4770, rebuilt to a Modified appearance in January 1945 after being wrecked in February 1944, differed from previous Modifieds in having an all-welded carbody, the type of construction famously utilized in the production run of the GG1. P5b experiment In October 1937, P5a #4702 was rebuilt with motors in its trucks to become the only locomotive in subclass P5b. Each truck axle was given a motor, adding to give a total power output of and a wheel arrangement of B-C-B or Bo′CoBo′. The main drivers had used on each axle, but the trucks were a single motor per axle. This modification also meant that locomotive's entire weight was carried on driven wheels. Despite these advantages the experiment was not repeated, however #4702 continued in its modified form. Visually, the class P5b could be distinguished from a boxcab P5a by having a lower row of ventilation grilles on the sides of the superstructure, and by having outside brake cylinders on the trucks. See also PRR locomotive classification References Baldwin locomotives General Electric locomotives P5 11 kV AC locomotives 4-6-4 locomotives Westinghouse locomotives Electric locomotives of the United States Railway locomotives introduced in 1931 Standard gauge locomotives of the United States Mixed traffic locomotives