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  • [an error occurred while processing this directive]

    Union Pacific "Double Diesel" Locomotives

    Author: John Oxlade, Salfords, Surrey, UK (EMail: )


    Background information on Union Pacific's fleet of "double diesels"

    Although the Union Pacific's gas turbines were considered a technical success, the rising price of the special bunker C fuel they used in the 1960s eventually made them less cost effective compared to diesels.

    In the early 1960s the UP approached the major locomotive builders (GM, GE and ALCO) to ask them if they could offer 3 locomotive sets with a total of approx. 15000hp. At this time, UP's motive power policy was essentially "big is best" and the 3 manufacturers came back with custom designed locos to meet their needs. All 3 of their offerings consisted of a long chassis supporting what was essentially 2 of their "standard" locos.

    GM offered UP a D-trucked cabless booster that was originally intended to be run with a normal loco (with a cab) in control. GM envisioned the new DD35 running between a pair of GP35s and produced a GP35, DD35, DD35, GP35 demonstrator set in a smart red and white livery. Although designed to UP's specific requirements the demonstrators were shown to several other roads, though only the UP and Southern Pacific bought any DD35s. The UP eventually bought all of the demonstrators (the 2 GP35s and 2 DD35s). Although intended to run with GP35s, there was no reason they could not be run with any other loco in control.

    EMD DD35 #73B

    The DD35 was originally intended to be built only as a "B" unit and the hood is virtually identical to that of a GP35 from the cab back, two of these placed on one chassis with the radiators towards the centre. After approx. a year, UP approached GM to ask for a version of the DD35 with a cab. Although mechanically very similar, the hood of a DD35A had flared radiators in much the same way as the prototype SD40s which were built around the same time, and also the later SD45. Documents from GM clearly note that the cabless loco was called a DD35, not a DD35B. It became necessary when the "cabbed" version came out to append an "A" to the name to differentiate those with cabs.

    EMD DD35A #75

    The DD35As had a standard 35-series cab with the narrow "nose" as on contemporary GPs and SDs of the period. The new D truck was only used on the DD35 and DD35As at this point, but was also later used on the DDA40X "Centennials".

    GE's offering to UP at this time was the U50. Similar in general concept to the DD35, it was basically 2 U25Bs on one chassis with a distinctive high-mounted, blunt-nosed cab. The radiators on a U50 were however mounted on the outer ends of the hood. The U50s rode on 4 AAR type-B trucks in pairs with span-bolsters from traded-in gas turbines. The U50s B-B+B-B wheel arrangement, the blunt nose and very prominent blowers at each end of the hood make them very difficult to mistake for anything else.

    Although the loco order allowed the UP to specify that the remaining locos be U25Bs, the UP was obviously satisfied enough with the first U50s as the order was filled in full. Photographic evidence confirms that it was quite common to have a U50 and a DD35 running in multiple

    GE U50C #5006

    UP returned to GE some time later to order a revised version of the U50 to ride on traded-in C trucks from the 8500hp gas turbines. The U50Cs had flared radiators such as those found on U36Bs and the hoods were turned round compared to a U50 such that the radiators were in the middle of the hood. The distinctive blowers from the U50 were also missing. These U50Cs were supposed to include several refinements but their downfall was in using aluminium (rather than the normal copper) wiring which tended to easily catch fire. The U50Cs were well known for suffering from electrical fires, and the entire fleet of locos enjoyed only a short service life. Some sources have used the name U50B or even U50D to differentiate between the original B-B+B-B and C-C trucked U50s, though "officially" GE only referred to them as the U50 and the later U50C.

    ALCO Century 855 #61

    ALCO's offering was the most powerful diesel delivered up to that time in the US, and the largest loco that ALCO ever built. The Century 855 was a 5500hp loco (GM's DD35 and the GE U50s were both 5000hp) and ALCO built an A-B-A unit demonstrator set. Like the U50s, the C885s rode on 4 AAR type-B trucks with span bolsters. The Century 855s were not very reliable and these 3 locos were the only examples built.

    Compared to the DD35 and U50, the C855 is a very "busy" looking loco with a design that looks as if it was cobbled together, and they had a distinctive fish-belly tank between the trucks. In comparison, the DD35 and U50 both show fairly clean, purposeful lines. The ALCO 251 prime movers in the C855's smoked in a typical ALCO fashion, and photos frequently show them under a large plume of black exhaust. In a letter from Rory O'Connor (an ex-UP employee who worked at North Platte), he stated that the C855s were superb locos on drag freights, but that it was their mechanical reliability and the pollution they caused (when America was getting very conscious of emissions) that was their eventual downfall.

    EMD DDA40X "Centennial" #6900

    In 1968 the UP returned to GM for an improved version of the DD35A. The first example of the resulting loco was completed in record time to enable it to participate in the centenary celebrations for the driving of the Golden Spike at Promontory Point, Utah in May 1969. They were numbered in the 6900s and from that point on were frequently referred to as "Centennials".

    The DDA40X had two 3300hp prime movers on a single chassis with flared radiators (as in the DD35A), but incorporates a "wide nose" cab. The name "wide cab" is misleading as the actual "cab" is always the full width of the loco, it is the short-hood that is either narrow or wide. Note: In the book "Centennials in Action", there is a copy of an EMD/GM delivery note that clearly identifies the loco as a DDA40X not DD40AX as sometimes quoted.

    DDA40Xs frequently ran in pairs and often had a "fast-forty" SD40-2 between. The 8000 number series SD40-2s (fast forties) were geared to run at the same speed as the Centennials, 79mph as opposed to 69mph on other locos. In reality this seems to have made little difference as many photographs exist of Centennials running with "other" locos, and the "fast- forties" were eventually re-geared and returned to their assigned (and reserved) number slots in the 3000 range.

    DDA40Xs are the only class of UP's double-diesels that have been preserved. In fact, one example is preserved by the UP and used for director's and other special trains.

    References:

    Cockle, George R., Giants of the West, Overland Publications, Muncie Indiana, ISBN 0-916160-12-2 Keekley, Rev. Harold, Roaring U50's, George R Cockle and Assoc., Omaha, Nebraska, ISBN 0-916160-06-8 Cockle, George R., Centennials in Action, Overland Models, Muncie Indiana, ISBN 0-916160-05-X


    [ last updated 31st Dec 2003 ]