The Pennsy - The Standard Railroad Of The World - had its own system of classifying diesel locomotives, rather than relying on the designations appointed by the builders of the units.

With very few exceptions, the Pennsy's diesels were classed using the following multiple character formula:

First Letter: Designates Manufacturer

E -- Electro-Motive Division (EMD) of General Motors
F -- Fairbanks, Morse & Company (FM)
L -- Lima-Hamilton Corporation
B -- Baldwin Locomotive Works (BLW)
G -- General Electric
A -- American Locomotive Company (ALCo)

Second Letter (and sometimes a third): Designates Service

F -- Freight
P -- Passenger
FP -- Freight-Passenger
PS -- Passenger-Shifter
FS -- Freight-Shifter
S -- Shifter
H -- Helper

Numerals: Horsepower (in hundreds)

Lower Case Letters: Denote Modifications

a -- New Engine of Body Style
m -- multiple unit control
s -- steam generator
z -- converted from passenger to freight service

Sources

From the "PRR-Talk" mailing list: Rich Orr, Derrick J. Brashear.

Last modified: December 31 2009.

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