Pennsylvania Railroad class P5

Two prototype locomotives were outshopped from the PRR's Altoona Works in 1931. They were essentially the PRR's 2-B-2 O1 design lengthened by adding another pair of driving wheels; while the O1 was an "electric Atlantic" equivalent to the E6s steam locomotive, the P5 was an "electric Pacific" designed to match or better the performance of the PRR's ubiquitous K4s Pacifics.

These prototypes had electrical equipment from both Westinghouse and General Electric; the design was by both companies and the PRR's electrical department, and the equipment from each manufacturer was identical.

Orders were placed for 90 production locomotives classified P5a due to minor changes from the prototypes (notably, larger traction motor blowers). Production was split between General Electric and Westinghouse; the GE examples were assembled at GE's Erie, Pennsylvania facility, still a locomotive assembly plant today, while final assembly for the Westinghouse order was subcontracted to the Baldwin Locomotive Works.

A fatal grade crossing accident on the New York Division confirmed traincrews' concerns about safety when the crew were killed after colliding with a truck loaded with apples. A redesign was undertaken, giving the locomotives a 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), P5am, and colloquially Modifieds.

File:PRR P5a mod.jpg

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.Wayt, Hampton C. (Fall 2010). "Update on the GG1's genesis". Classic Trains (Kalmbach) 11 (3): 86–87.

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,{{Cite news

|title=2 Killed as 90 Car Freight Speeds Past Flagman and Plows Into Standing train

|newspaper=Philadelphia Inquirer

|date=February 14, 1944

|page= 1

}}{{Cite book|title=Investigation no. 2774 The Pennsylvania Railroad Company report in re accident near Roxton, Pa., on February 13, 1944|author=Interstate Commerce Commission|oclc=947002343}} differed from previous Modifieds in having an all-welded carbody, the type of construction famously utilized in the production run of the GG1.{{cite book

|last=Volkmer |first=William D.

|title=Pennsy Electric Years

|year=1991

|publisher=Morning Sun Books |location=Edison, New Jersey

|isbn=1-878887-01-7

|pages=26–27

}}

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 {{convert|375|hp|adj=on}} motor, adding {{convert|1500|hp|abbr=on}} to give a total power output of {{convert|5250|hp||abbr=on}} and a wheel arrangement of B-C-B or Bo′CoBo′. The main drivers had used {{illm|double traction motor{{!}}double traction motors|de|Zwillingsmotor}} 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.

• PRR locomotive classification

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Category:Baldwin locomotives

Category:General Electric locomotives

P5

Category:11 kV AC locomotives

Category:4-6-4 locomotives

Category:Westinghouse locomotives

Category:Electric locomotives of the United States

Category:Railway locomotives introduced in 1931

Category:Standard-gauge locomotives of the United States