EMD (Electro Motive Division) first established numerous prefix and suffix designations during the early years
MP GP40 unit

A "General Purpose", "40 Series" (GP40) owned by the Missouri Pacific (MP) portion or subsidiary of the Union Pacific (UP) during the 1982 merger.

of their establishment as the Electro- Motive Corporation (before the GM merger in 1937; excluding the CAT purchase in 2012, to which the name never changed other than "Division" being altered to "Diesel"). They initially began designating their various types of diesel locomotives as follows:

Early (Pre-EMD) Prefix MeaningsEdit

BL - "Branchline"

E - Originally meant "eighteen hundred horsepower" (1,800hp); designation of all EMD 6-axle, A1A-trucked cab units.

F - Originally meant "fourteen hundred horsepower" (1,400hp); designation of all EMD 4-axle cab units.

FT - Cab unit; fourteen hundred horsepower or "Freight" (though, the "Freight" designation was eventually ommitted once railroads began utilizing their FT units for passenger service as opposed to utilizing E units; such as the ATSF)

FP - Passenger service (equipped with a steam generator; unlike later types long after the GM purchase)

NC - Nine hundred horsepower (900hp); cast frame

NW - Nine hundred horsepower (900hp); welded frame (though, the term as eventually used for classifying the condition of the frame being "New Cast" to better differentiate between the early "SW" models)

SW - Six hundred horsepower (600hp); welded frame (though, eventually designated as "switcher" from 1937-onwards)

T - "Transfer"

Later (1937-onwards) Prefix MeaningsEdit

DD - Eight-axle locomotive with 'D' trucks (or "Double Diesel")

F - Cowl locomotive (protective carbody; like on the F45 or SDP40F)

GP - "General Purpose"; road switcher with B-B axle arrangement

SD - "Super Duty" (or "Special Duty"); road switcher with C-C axle arrangement

P - "Passenger" (as with such models as the GP40P-2, SDP35, and the original SDP40)

RS - "Road Switcher" (as in RS1325; though the designation was originally used with ALCO for their "RS" series)

SW - "Switcher" (as seen above)

Suffix MeaningEdit

A - Cab unit (locomotive with cab and controls).

AC - Alternating current electrical systems (such as with the GP38AC)

MAC - "Modified AC-traction" (such as with the SD70MAC, SD80MAC, and SD90MAC).

R - "Rebuild" or "rebuilt".

A former Conrail NS (Norfolk Southern) SW1 built in 1947 originally for the Pennsylvania Railroad (PRR), is an example of a "Switcher" with 600hp and a welded frame.

W - For "Wide" when referring to early Canadian-built models utilizing or containing an early wide-cab

B - "Booster" unit (cabless locomotive without cab and controls).

C - For C-C (six-axle trucks)

F - Cowl (protective carbody; as mentioned).

I - "Isolated cab" or "improved" (as with the SD70I and subsequent "isolated" variants of the SD70 without the "I" designation)

M - "Safety Cab" (or "modified"; as with the SD60M and SD70M; minus the "AC" suffixes as evident with the SD60MAC and SD70MAC).

PH - Passenger locomotive with head-end power or HEP; as with the F40PH (though earlier units were originally fitted with steam generators).

T - "Tunnel" (for the "Tunnel Motor" series consisting of having locomotives with large air intakes located on the running boards or sides of the carbody as part of an advanced cooling system; such as with the SD40T-2).

35 - Number of series (such as the SD45, GP35, F7, etc.)

Other PrefixesEdit

MP - "Multi-purpose" (as in the MP15 series)

Other SuffixesEdit

e - "Enhanced" ("energy-efficient" or "eco-friendly" as implied with the SD70ACe)

T - "Turbo" or "Turbocharged" (like with EMD's MP15T built specially for CSX)