When is an EMD "F7A" an "EF15a"? When it's owned by the Pennsylvania Rail Road!
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.
When the Pennsy first started purchasing diesel locomotives, they extended the classification system used for steam and electric locomotives, which was based on wheel arrangements. This sort of worked, until the arrival of the EMD E7's. The E7's were paired so "one unit" would have 4,000 hp. This produced a "powered" wheel arrangement of 0-6-6-6-6-0!
They decided to count the total number of trucks...
Example: A pair of EMD E7's would be class 4B
On April 26, 1946, desiring to account for three axle trucks with the middle axle being unpowered, the system was quickly modified, with numerals indicating the unpowered axles.
Example: A pair of EMD E7's would be class A1A-A1A
Second Classification System
On July 1, 1946 a new system was adopted to address these shortcomings.
First Letters (in parenthesis): Designates Truck Arrangement
(B-B) -- Two, two axle trucks
(C-C) -- Two, three axle trucks
(A1A-A1A) - Two, three axle trucks with the middle axle unpowered
Etc.
Numerals: Horsepower (in hundreds)
Suffix 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)
Example: A pair of EMD E7's would be class (A1A-A1A)20E
On April 1, 1947, anticipating the arrival of the first B units, the railroad modified the system once more. Now it would place a numeral in front of the prior class, indicating the number of locomotives in the lashup, and the class would indicate the truck arrangement within one locomotive.
Example: An ABA lashup of EMD E7's would be class 3(A1A-A1A)20E
This system went "out the window" with the arrival of the permanently coupled "Centipedes" which would have been class (2D+D2+2D+D2)60B.
Third Classification System
In May, 1947, a third new classification system was introduced. Each unit in a lashup carried its own individual classification.
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
For Switchers, Numerals (after a dash): Horsepower (in hundreds)
Example: An Baldwin VO 660 would be class BS-6
For Road Units, Numerals (after a dash): Number of Units in Lashup
Example: An ABA lashup of EMD E7's would be class EP-3
This system had its shortcomings with the arrival of E8's and other road units where the horsepower could not be discerned from the class and they often ran in AA lashups.
Fourth Classification System
In September 1951, the fourth classification system was adopted. It would remain in effect until 1966 when a classification system, based on this system, was created for the merger with the New York Central.
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 (after a dash): Horsepower (in hundreds)
There is debate of the use of the dash. The dash is not present on the painting and lettering diagrams.
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
Example: An EMD E7 would be class EP-20
