California's Railroad to the U.S. 1861 - 1996

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SP Diesel Classes in 1964

Prior to the big locomotive renumbering in October 1965, SP diesel locomotives were classified according to a scheme that was derived from their steam locomotive classification scheme. There were three overall categories:

Diesel Passenger (originally DEP for Diesel-Electric Passenger). This category included only cab-type passenger units, not hood units or any F7 or FP7 units purchased for dual service.

Diesel Freight (originally DEF for Diesel-Electric Freight). This included all the dual-service locomotives; it also included switchers purchased as light road units (e.g. the SW8's, and some of the S-6's).

Diesel Switcher (originally DES for Diesel-Electric Switcher. This included all the switcher-carbody units purchased specifically for switching.

Within each category, each separate order was assigned a sequence number. Originally these sequence numbers were simply assigned starting at 1 (so, the first diesel road freight units ordered by the SP, the F3 units purchased in 1947, were assigned class DEF-1). Eventually, however, SP found it necessary to allocate sub-categories for diesel freight units, with each hundreds group allocated to a different sub-category. Orders were sequentially assigned sequence numbers within their subcategory. For example, the first diesel road-switchers acquired by the SP, the Baldwin DRS6-4-1500 units of 1948, were assigned class DEF-100 (I think). A somewhat similar scheme was applied to the switchers.

Diesel Freight Sub-categories

I've never seen a complete breakdown of all the sub-categories of diesel freight units the SP used. This is my best guess based on the information in Strapac's Southern Pacific Historic Diesels series and information from the web and other sources.

Sub-categoryDescriptionFirst Delivered Units
1-99Cab-type units, both A-units and B-units (F3, F7, FP7) EMD F3's, 1947
100-199Six-axle low-horsepower (<2400) road-switchers, including boostersBaldwin DRS6-4-1500, 1948
300-399Low-horsepower (<1000) light road-switchers (w/MU and train indicators, ptd. in Tiger-Stripe w/aluminum ends) EMD TR6 cow-and-calf, 1950
400-499High-horsepower (1000+) light road-switchers (w/MU and train indicators, ptd. in Tiger-Stripe w/aluminum ends)T&NO EMD SW9's, 1951
500-599Six-axle high-horsepower (2400+) road-switchersFM H24-66 units, 1953
600-699Four-axle road-switchersT&NO EMD GP9's, 1954
700-799Diesel-hydraulic unitsKM ML-4000 units, 1961
800-899Eight-axle road-switchersEMD DD-35, 1964

As it happens, these sub-categories are in increasing order of the first delivery of units within the category.

courtesy Larry Allen

SP Diesel Classes in 1965

Naturally SP had their own system of class designation, other than the manufacturers designation, and different again to the model designation. Railfans and authors of SP texts, have also 'coined' their own terms, which can really confuse the issue.

Extra 2200 South is the main perpetrator of this, with their 'Phase' designations, these are totally unofficial, but extremely helpful to railfans and modelers, at which these sort of detail differences are really aimed. Historians no doubt disagree with this entirely.

SP changed their system a couple of times, starting with the first deliveries of diesel switchers, these were designated DES, which I assume stands for Diesel Electric Switcher, this was later shortened to DS. The road freight units were initially classified DEF, passenger units were DEP, in December of 1950 these were shortened to DF and DP.

The alpha was followed by a numeric, which appears to have been assigned sequentially, eg. the EMD SW1 was class DES-1 later (DS-1), the ALCo HH-660 was class DES-2 (DS-2) as so on. This lasted until DES-7, when there appears a jump to DES-100.

The first SP road units were EMD F-3 units class DEF-1 (DF-1), prior to these were the Cotton Belt EMD FT units, Cotton Belt for quite some time, went their own way with paint schemes and units rostered, their class designation was no different the FT's were classed Z 13.5 B-B, their first switchers were Baldwin VO-1000's class Z 10 B-B. from this one can assume that 'Z' means diesel, the number is horsepower in 100's, and B-B is the truck arrangement.

With the system-wide renumbering in September 1965, came a reclassification which grouped similar units in the same class and number series. A change was made to a builder based system, with the builders initial as the start, followed by a letter denoting service, then a number consisting of the axle count and (approx) horsepower, another letter designated a cab (A) or booster unit (B), a 'C' if Cotton Belt owned, 'D' if DRGW owned (after 1988), and then the actual class, by purchase order. When fully owned? units later came up for the Rebuilding program, they were sold to the SP Equipment Co. a letter 'E' denoting that ownership and gained an 'R' if rebuilt under the GRIP program. Only GP35's rebuilt under contract by Canadian National received the 'N' designation.

Corrections to any of the above welcome...

A = ALCo F = Freight 4 = BB hp in ~100's
eg. 06=600
A = Cab Unit actual class number, in order of purchase, SSW units had their own sequence
B = BaldwinB = Booster unit
E = EMD P = Passenger 6 = CC C = Cotton Belt
F = Fairbanks-MorseE = Later if rebuilt and sold to SP Equip. Co.
G = GE S = Switcher 8 = B+B-B+B or DD S = Later if rebuilt and sold to SP Equip. Co. and leased to SSW
K = Krauss-MaffeiR = If rebuilt under the GRIP program
K= Rebuilt by Morrison Knudsen
N = Rebuilt by Canadian National

Examples using the above Table:

SP EMD SW1 was a DES-1 later DS-1
in 1965 it would have been ES406-1

SP EMD SW900 #4629 was initially DS-306 then DS-606
in 1965 renumbered 1175 and classed ES409-2
sold to the SP Equipment Co. and rebuilt to SW900E renumbered 1190 and classed ES409E-1

Cotton Belt VO-1000 #1022 initially classed Z 10 B-B by Cotton Belt
became BS410C-1

A few more quick examples:

  • FM H12-44 #1486 - 1491 = FS412-1
  • ALCo PA-1 #6011 - 6016 = AP620A-1
  • ALCo PB-2 #5920, 5921 = AP620B-1
  • GE U30C #7900 - 7929 = GF630-1
  • DRGW SW1000 = ES410-D01

Further reading for Rebuild Programs see: Sacramento Locomotive Rebuild Programs

As I only ever intended my website to cater for modelers, I did not feel the need to include this information, so generally you will not find it on my pages. However, with the development of this FAQ, and the information being offered on the SP Mailing List, there does seem to be a requirement, if not for the inclusion, at least for this explanation.

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Sunday, October 06, 2002