Union Pacific's DDA40X Centennial Locomotives

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by Don Strack

This page was last updated on June 17, 2024.

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(This article is an updated and expanded version of an article published in Diesel Era, Volume 13, Number 6 (November/December 2002)


Union Pacific's Centennial locomotives were the largest railroad locomotive in the world. These distinctive giants dominated the railroad's western mainlines from 1970 through early 1980, and were seen on all of the railroad's most important trains. Built as a unique-to-UP design, they were constructed by the Electro-Motive Division of General Motors Corporation.

Numbered as UP 6900-6946, they were known as "Centennial" locomotives because the initial deliveries started on the 100th anniversary of the May 10th 1869 driving of the golden spike at Promontory Summit, Utah. UP 6900 was rushed to completion to allow it to be part of the various ceremonies that took place in Utah on May 10th 1969. Delivery of the rest of the units began a month later and continued until September 1971. The 6900s were delivered in two groups: UP 6900-6924 (delivered in June to December 1969), and UP 6925-6946 (delivered in June 1970 to September 1971). The two groups were identical except for some very minor differences.

These 47 locomotives were the longest diesel locomotives ever built, at 98 feet, 5 inches. Their frames were too long for EMD to manufacture and were fabricated by the John Mohr Company of Chicago. Their fuel tanks were also the largest of any diesel locomotive, with a capacity of 8,000 gallons of diesel fuel, making the fuel tank weigh 30 tons fully loaded.

Quest for Larger Power

The Centennials were the final example of Union Pacific's search for the ideal locomotive. This search stems from the steam days in the mid 1930s when the first high-speed 4-6-6-4 Challengers arrived. It continued through the years of the Big Boy 4-8-8-4 steam locomotives, and the years of the Standard, Veranda, and three-unit gas turbines. The search continued during the diesel era with the DD35s, DDA35s, U50s, and Century 855s of the mid 1960s.

Beginning in late 1967 the road pursued a study of its motive power design needs. In the mean time, in March 1968, and as a stopgap measure, UP tried EMD's SD45 as a high-horsepower, high-speed locomotive, but with limited success. By that time in early 1968, the road had a better picture in mind of what it needed for high-speed, over-the-road motive power and was looking for more big power. Coincidently, EMD was itself looking to integrate some new reliability features into a new locomotive design. The DDA40X Centennials were the result of a collaboration between the railroad and the builder.

Within 13 months of the initial March 1968 communication, the railroad and the builder had worked out a definitive design and the first unit was delivered in late April 1969. The new locomotive was much different in its design. Although in concept it was an improved version of the earlier DDA35, which itself was a version of the initial DD35 booster unit with a cab. From the very start, the DDA40X design was conceived and executed to be as maintenance-free as possible, but still deliver maximum horsepower output. EMD applied the DDA40X model to these units because they were experimental (denoted by the X in the model designation) and were essentially a design built to test many of the features that the builder would later use in its Dash 2 line, beginning in 1972. The most important features included self-loading and electrical control modules.

In a September 1969 speech before the annual meeting of the Locomotive Maintenance Officers Association, David S. Neuhart, UP's top mechanical officer (Title: Superintendent of Motive Power and Machinery) counted off 14 points of design improvements. First on the list was self-loading, a new feature first applied to the Centennials that allowed maintenance forces anywhere, with the flip of a single switch, to load check a unit without the need of a trackside load box. This feature was later used in January 1972 with EMD's new Dash 2 line, and is a feature that remains part of every design from EMD since then.

Another feature that found its way into the Dash 2 line following a test on the Centennials, was the modularized control circuits, which made troubleshooting considerably easier. Other list items included improved electrical control, improved mechanical features, an integral frame and 8230-gallon fuel tank, stronger pilot design, heated windshields, unitized air brake components, and a hand brake located in the cab interior.

Locomotive historians Jerry Moyers and Jim Boyd further describe UP's Centennial locomotive: "The unit was to pack two 16-cylinder 645E3A engines driving alternators for 6600 h.p. (marking the first horsepower increase for the basic 645) within a 98'-5" carbody in hood unit configuration, but sporting a wide cowl nose similar to the FP45. Weighing in at 270 tons, the DDA40X was labeled as 'The World's Largest and Most powerful Diesel Electric Locomotive'."

All of the Centennial units were equipped to operate at 90 miles per hour, using EMD's standard high speed 59:18 gear ratio. They were also classified as having pilot snow plows, although the definition was a bit loosely applied; the units only had angled, vertical pilot plates, and were not equipped with formal snowplows, such as many of UP's other road units.

The 6900 class averaged 22,000 in-service miles per month. Such high mileage also required high maintenance. Within five years, most of the units in the class had racked up over 1,000,000 miles. In March 1976, UP initiated what it called a "Fail-Free" program because of the high miles these units had seen after five to six years of high mileage service. The program was meant to improve the units' reliability and was completed in April 1977 by the shop forces at Omaha, Nebraska, and included reconditioned electrical components, main generators, engines, and traction motors. Another "Fail-Free" program was begun in late 1978.

Paint Scheme Changes

In September 1969, the wording on the UP medallion (shield) was changed from "Union Pacific Railroad" to just "Union Pacific." This change reflected the new Union Pacific Corporation, organized in January 1969 as a holding company for the railroad and all of its non-rail subsidiaries.

The most visible evidence of the change came on the 6900-series Centennial units. UP 6900-6924 were delivered in April to December 1969, and 60-inch medallions were applied along with lettering and numbers by UP at their Omaha Shops. The first 25 units received 60-inch medallions with "Union Pacific Railroad" spelled out. After the wording on the shield was changed, plain blue paint was used to cover the word "Railroad". As updated 60-inch shields became separately available in mid 1970, they were applied to units with the painted-out shields. Some units retained their "crossed-out" medallions as late as 1973 (UP 6904, 6923) and 1974 (UP 6903). Photos taken in the late 1970s show that most of the Centennials had the newer two-word version. Other units with smaller shields had them replaced by other paint shops as the updated shields became available.

UP 6925-6946 were delivered in June 1970 through September 1971 with the updated version of the large shield, with only "Union Pacific" spelled out, although photos of at least three units (UP 6928, 6929, 6932) show that some did receive "Railroad" medallions, with the word painted out. (Listing of 6900-series units with and without 'Railroad' on the medallion.)

In Service

The Centennials were usually used on UP's high-speed, mainline, fast freights. At times, they were likely also used on the secondary freights, and even on some of the heavier "locals", which usually had all types of UP's heavier motive power. One report from Pocatello shows that on at least three occasions in 1979 and 1980, Centennials were used on locals between Idaho Falls and Pocatello. On one occasion, the "Roberts Local" between Pocatello and Idaho Falls made use of what railfans call a "Fast Forty Sandwich", meaning two Centennials back to back, with an 8000-class SD40-2H between them. This Roberts Local was usually quite heavy, since it gathered potatoes from the various warehouses every night, and moved them to Pocatello for classification.

The units all accumulated about 2 million miles over their service lives. The units generally worked out of North Platte, Nebraska. North Platte to Los Angeles is 1200 miles. North Platte to Portland is 1300 miles. During 1975, the 6900s averaged 15000 miles per month. During 1976 it was about 17000 miles. And during 1977 it was about 19000 miles. They were generally in service from 1970 to 1980. That's at least a total of 1.8 million miles for each unit. Some were used less. Some were used more. While other documents may show different mileage figures, including mileage since the most recent overhaul instead of total mileage, the most reliable source seems to be monthly mileage reports for UP's entire diesel fleet, broken out by specific model type.

Rob Leachman wrote on August 26, 2004:

The Centennials were all equipped with experimental "advance excitation" of the traction motor fields. They could get a forwarder train up to speed faster than anything on the rails. I remember Jack Bowen, UP General Superintendent of Transportation, stating in a staff meeting that substituting any other power for Centennials on the North Platte - Ogden segment of the Overland Mail train would require adding 45 minutes to the schedule (just because of the time difference accelerating out of terminals, restrictive curves and slow orders). I also recall that in the early 70s, UP would regularly add a unit in Pocatello to the 2 Centennials that brought WB forwarder trains out of North Platte. (Another unit was needed for tractive effort to get over the steep grades on the Northwestern District. A similar policy was adopted for South Central District hot trains west of SLC.) The extra unit was often added on the point. When these trains started up, one could see and hear the Centennials bump the leading unit. The walk-over plates on the extra units (typically GP30s, GP35s, GP40s, or SD40-2s) were always dented in because the Centennials would be pushing them along whenever the power was accelerating. By 1975, UP was powering the forwarder trains with 3 Centennials (one LA RT started getting four) instead of with mixed units, just because any other power could not keep up with the Centennials. In the late 70s, when "Big Mac" lash-ups (2 Centennials bracketing a high-geared "fast forty" SD40-2) became the norm, I bet they still could not quite match the same running times as the previous all-Centennial lash-ups, even at the same HPT.

After a decade of non-stop operation in the most demanding high-speed freight service imaginable, it's little wonder they started to fall apart.

UP easily got its money out of these units and then some. Despite longer-mileage routes to the Pacific Northwest than BN and to LA than ATSF, UP walked away with the lion's share of the merchandise and other time-sensitive businesses.

Rob Leachman wrote on May 18, 2005:

The DD40AXs had the highest Return On Investment (ROI) of any power UP ever owned (up to their time). Day in and day out through the 70s, they raced the high-revenue hotshots NoP - LA and NoP - Portland and back. Back when "Dependable Transportation" really was. They could take a train NoP - Ogden 45 minutes faster than any other power on the roster (at the same horsepower per ton), even other 59:18 units, simply because the advance excitation of their generator fields could accelerate them out of the curves that much faster. Assigning SD40-2s to a hotshot was the kiss of death, it meant that train would not be making up any time lost by the Iowa Lines today. All the Centennials accumulated more than 2 million miles in only a decade, show me any other contemporary freight power to do that. The fact that their service lives could not be extended to 10 million miles is hardly an indictment of them.

Rob Leachman wrote on January 24, 2009:

Before the Centennials were stored (early 80s), they were very popular with the engine crews. They were a tremendous source of pride throughout the company. After they came out of storage they weren't the same. Problems with the units, rare in the 70s, became more common as their age was showing and the harmful effects of long-term outside storage were apparent. From a railfan point of view, the show after they came out of storage was much less impressive, with only one or two Centennials on a train, usually mixed with SD40-2s, in lieu of the impressive 3-unit and 4-unit lash-ups of Centennials common back in the 1973-75 era.

Very smooth riding and pretty quiet in the cab comapred to its contemporaries. The acceleration beat the pants off of anything else. In Omaha we found that a set of Centennials on average could make the run North Platte to Ogden 45 minutes faster than any other motive power at the same horsepower per ton. On the Hinkle - Kenton run down the Columbia Gorge, a good engineer on a set of Centennials with green signals the whole way could do the run in three hours. Impossible with any other power back then.

The Centennials were normally assigned to hot trains with high horsepower per ton, so when you were called to take a train wih a 6900 on the point, it almost always meant you were going to get a good run.

The Centennials were high-speed merchandise engines. They were not mountain luggers. The engineers in the Blue Mountains preferred to have a set of SD40s. But just about everywhere else on the system, they were the favorite of the crews.

In the 70s the UP did a tremendous job of winning and keeping the lion's share of the time-sensitive merchandise traffic Chicago - PNW, Chicago - Bay Area, and Chicago - LA. The Centennials were a key part of their very successful strategy.

Post MoP-UP, it became hard to imagine that the UP was once like that. Nowadays, the BNSF is in that role (inheriting it from the 1990s ATSF).

The Centennials had 59:18 high-speed gearing as opposed to the 62:15 gearing on everybody else's freight EMDs. Also, they were the first EMD units delivered with advance excitation to the traction motor fields. When lashed-up behind 62:15 units, the 6900s would bump the 62:15 units a bit when starting.

There was more hot merchandise traffic to/from So Cal than to the Pacific Northwest, so more Centennials went that way. But UP tried to put Centennials on all the hot trains to/from both the Pacific Northwest and So Cal, there wasn't any favoritism. In the 1971-1973 era, there were three pairs of trains each way NoP - LA and two pairs of trains each way NoP - Portland and one train each way Portland - LA that usually were assigned pairs of Centennials, with a district-option third unit added on the Pacific Northwest and LA&SL grades. Beginning in the summer of 1973, the hottest of the round trips to LA began running with three Centennials. Then in summer of 1974, that round trip (VAN and LAX) was increased to FOUR Centennials, and the hottest round trip to Portland (NCV and SPX) was increased to three Centennials. The growth of intermodal traffic and fuel conservation concerns led to the re-gearing of a batch of SD40-2s into the 8000 class units, and so beginning in 1976 the "Big Mac" lash-ups of two Centennials bracketing a Fast Forty became the rule. Trios and quartets of Centennials became memories.

After coming back from storage in the early 80s, there were many less Centennials to go around plus the need to power the Bay Area trains, and the big units were not so reliable anymore, so multi-Centennial lash-ups became rare. Usually it was just one or sometimes two plus SD40-2s.

From my point of view, the most interesting assignment of Centennials was on the PLA (hot paper loads from Oregon-Washington to Sou Cal), returning on the SSS (handling the hot GE Clearfield merchandise to the PNW). The SSS was one of the last great high-speed boxcar merchandise operations.


Only two units were retired during regular service, both due to wreck damage. UP 6903 was wrecked on Cajon Pass in southern California on April 6, 1974. After the wreck, the unit was moved to UP's Salt Lake City shops and stripped of any usable parts. The remaining frame, along with the unusable components shipped in gondolas, was sold for scrap in June 1974 to the Purdy Company at Lakepoint, Utah. UP 6921 was wrecked on August 27, 1978 at Point of Rocks, Wyoming. It too was moved to Salt Lake City, where during September 1978, the usable parts were removed. The frame was finally sold in February 1979 for scrap to the Durbano Company at Ogden, Utah.

Removed From Service

The high maintenance costs due to these unique units' high mileage was their downfall with the severe business downturn in 1980. Many of the units had accumulated as much as 2.2 million miles. The newest units were only nine years old, and the oldest were 11 years old. UP had hundreds of much newer and more reliable SD40-2s to use on its trains, so the 6900s were soon removed from service. (Rumors among the rail enthusiast community, and among the railroad's employees was that because each Centennial had two diesel engines, when one diesel was out of service, the power of the other engine was idle and therefore wasted - but this was never a consideration for whether or not the units were sidelined.)

The combination of newer, more reliable units, along with the improved technology on those same new units (SD40-2s from General Motors, and C30-7s from general Electric), were what caused these "double-diesel" units to be retired. Also, there was a growing concern about frame cracks. Another concern was that UP's run-through partners flatly refused accepting the Centennials on their railroads.

The fuel tank on the DDA40X locomotives was integral with the frame and the frames began showing signs of cracking at full fuel load of over 8,000 gallons. A review of photos will reveal a vertical brace between the side sill and the fuel tank from the early 1970s on, an attempt to control the flexing on the long frames/fuel tanks. Due to the severe flexing, the inadequate brackets very soon started popping their mounting bolts. There were also a multitued of cracks along the bottom where the fuel tank wrappers were welded to the frame members. The frame/fuel tank welds were a point of underside inspections whenever possible. Due to the concerns about cracked frames, there was a directive about a maximum of 6,000 gallons from the mid 1970s on.

Don Strack wrote about the fuel tank support brackets on January 18, 2016.

I was working afternoon shift at the time. It was guys on day shift that were doing the work, and complaining loudly about how silly it was. After a review of online photos, you are right, it is only on second order units. Maybe it was just one or two units, or maybe they were having to drill out broken bolts and replace them. I was never a big fan of these monsters, so I guess I tended to ignore them when I saw them. I know at least two had their fuel emptied and were put on house steam for two days so that the cracks could be welded. Those were big fuel tanks, and the shop guys had to scrounge some big steam hoses, one for each side. We usually removed any fuel tank we repaired, and set it on the shop floor. But not for the Centennials. Since the cracks were along the bottom, where the sheet metal was attached to the frame rails, the welders had to repair the cracks overhead, while the locomotive sat over an inspection pit. This meant one of the shop tracks was tied up, and other units could not be moved in or out. I was a pretty good welder, but not good enough to do overhead fuel tank welds, so I missed out on the overtime. Overtime for wreck repairs was good bonus income, and I did a lot of wreck repairs.

The Centennials were almost solely on run-through trains all through the late 1970s, and Salt Lake didn't work on them all that often, which to me was a good thing. Like the DD35s and DDA35s before them, there was two of everything, and it was all crammed together to save space, making everything hard to work on. An inch of clearance here, or two inches there, makes a lot of difference. I quit in 1979, before they were stored in 1980. I took a few photos in 1984 when they returned to service, but not all that many. I was a modeler at that time, and only took photos of locomotives to help in my modeling, and I knew for sure I had no intentions of modeling the Centennials. Too many bad memories. Back in 2012 when Athearn released their HO model, I happen to be at a local train show, and Athearn had a big display, with their new Centennial model front and center. The factory rep approached me when he saw me leaning in to get a closer look. We visited for a couple minutes. I told him I worked on the real thing off and on for almost 10 years, and appreciated all the work that went into the model, but I was more a fan of GP9s than of Centennials.

The Centennials were mostly used on interstate run-through trains. While they were used systemwide on all the mainlines, they were usually assigned to North Platte to California, and North Platte to Portland/Seattle trains. They were fueled at Rawlins, Wyoming, and North Platte, Nebraska, and topped off as needed with service trucks at other locations. UP tried to avoid full refueling in California due to high fuel taxes there.

During May 1980, after barely a decade of service, 25 units were placed into storage at Council Bluffs, Iowa, across the Missouri River from Omaha, with 12 more being stored at North Platte, Nebraska. Within a couple months, the other eight most recently rebuilt units were stored at Salt Lake City. By August 1980, reports in the railfan press indicated that all 45 remaining units (minus wrecked 6903 and 6921) were out of service and in storage.

According to information gleaned from UP's COIN computer system, on June 22, 1980, the following 23 Centennials were stored: 6900, 6904, 6907, 6910-6916, 6918-6922, 6924, 6926, 6928, 6929, 6934, 6939, 6943, 6944. A trace from July 3, 1980 shows that 6905 was stored at North Platte after arriving June 22nd on the SLNP-21, and 6937 was shown at Los Angeles since June 1st. UP 6936 had been at Council Bluffs since June 14. A similar trace dated August 30, 1980 showed the following eight Centennials still in service: 6902, 6909, 6925, 6930, 6932, 6938, 6942, and 6946.

UP 6901, 6908, 6917, 6923, 6927, 6931, 6933, 6935, 6940, 6941, and 6945 were all shown as stored at North Platte after their final runs in the July 8 to July 20 time frame, with UP 6935 being the last of the 11 units to arrive at North Platte, on July 20. Some may have made additional runs later in July or August, but no records remain that show them in service. Another trace dated October 13, 1980 showed just eight units still in service: 6902, 6909, 6925, 6930, 6932, 6938, 6942, and 6946.

In October 1980, reports in the railfan press showed that the 37 units stored across the system were moved to Las Vegas, Nevada. But a trace dated January 15, 1981, showed the same eight units still in service: 6902, 6909, 6925, 6930, 6932, 6938, 6942, and 6946, along with a reactivated 6908. Additional information from late February 1981 showed that the last of these nine remaining units ran on February 20, 1981, although the specific road number was not recorded. The last nine units were sent to Salt Lake City (and later, Ogden) for storage, where they remained for another year. In January and February 1982, the remaining 45 units (36 units at Las Vegas and the nine units at Salt Lake City and Ogden) were gathered together and moved to Yermo, California, where they would remain for another two years.

In 1982, with all 45 remaining units in storage, UP tried to negotiate a deal with EMD to use the 6900s as trade-in on additional SD40-2s, but an agreement couldn't be reached.

In April and May 1983, with all of the units in storage at Yermo, UP began removing the Coded Cab Signal (CCS) equipment from some of the stored 6900s to allow the equipment to be shipped to C&NW for installation in C&NW SD40-2s and GP50s. This would bring to an end the practice of using UP pilot units on C&NW run-through trains from Fremont to North Platte, Nebraska.

In late 1983, the economic recession of the early 1980s was slowly coming to an end, and rail traffic was increasing. UP soon found itself holding trains for want of locomotives to pull them. With the slow increase of business, UP again approached EMD with a potential order for SD40-2s, but by this time EMD was only offering SD50s and GP50s. UP had borrowed GP50s from C&NW and SD50s from other roads and had not been impressed with their performance. Also, EMD couldn't make delivery for at least several months. (The post merger, and still independent Missouri Pacific received SD50s in November and December 1984). Since the Centennial units couldn't be traded to EMD, UP then looked at returning them to regular service, especially those that were either in good condition, or that could rapidly be brought up to good condition.

Return To Service

In early September 1983 UP began moving some of the 6900s to Salt Lake City for removal of the diesel engines, which were then installed into UP's high-mileage SD40-2s. As the engine removal program progressed, at a rate of about two to three locomotives per week, many of the 6900s were found to be in better shape than some of the SD40-2s that were to receive the replacement engines. This new development in the units' condition forced UP to rethink this particular replacement program.

To investigate a return to service for the Centennial fleet, UP 6938 and 6942 were removed from storage in mid-January 1984 to look into a rebuild program for the 6900s to get the locomotives on the road as soon as possible. The rebuild program would be expensive, but still cheaper than new SD50s, and UP would have had to wait several months for new SD50s. In late February 1984 UP began moving 40 of the Centennials out of storage at Yermo to Salt Lake City, and to North Platte, to return them to service.

Five serviceable units remained at Yermo: 6920, 6926, 6928, 6939, and 6944. Within a month there were 25 units back in service, including 6902, 6905, 6908, 6910, 6912, 6913, 6914, 6916, 6917, 6918, 6922, 6923, 6924, 6927, 6929, 6930, 6931, 6934, 6935, 6936, 6938, 6941, 6942, 6943, and 6945. Part of the task to return serviceable units to active service was to insure each was properly equipped with Coded Cab Signals. Some of the CCS equipment was removed from units that were otherwise unservicable.

In April 1984, the remaining 15 units were found to be unserviceable and were returned to storage: eight (6900, 6901, 6906, 6909, 6925, 6932, 6933, 6937) were returned to Yermo; three (6904, 6907, 6919) were at Salt Lake City; and four (6911, 6915, 6940, 6946) were at Omaha/Council Bluffs. On June 25, 1984, these 15 unserviceable units were retired and stripped of all parts that could be used to keep the 25 operational units running.

Each of the 25 units that were returned to service were allowed to operate on any part of the Union Pacific system. This included being equipped to work with end-of-train devices for cabooseless operations between Salt Lake City and Los Angeles after October 1984. (Cabooses were still required between Nampa, Idaho and Portland, Oregon, until September 1985.)

By late 1984 the traffic surge had played itself out and all 25 operating units were removed from service on December 23, 1984. In the following months, as many as 14 units saw limited service but by early April 1985 all of the remaining 6900s were officially out of service, awaiting retirement and disposition. Reliability remained a problem, with 10 of the units in service during 1985 (6914, 6916, 6917, 6927, 6929, 6930, 6941, 6942, 6943, and 6945) being removed from service specifically because of their record of failures.

The big units were no longer needed because UP was owed horsepower-hours by other roads and was able to use pool power from these other roads, putting the 6900s, and other Priority III units like them into storage. The last 6900s to go into storage were 6902 and 6938, with their last day of operation being on April 16, 1985. UP 6936 was the last operating DDA40X on the railroad. It made its last regular freight trip on May 6, 1985. UP 6936 was officially removed from regular service and was transferred to the heritage fleet at Cheyenne. The unit was used on an excursion train on May 24, 1985. During February 1986 five of the retired units were stored at Salt Lake City (6910, 6918, 6932, 6935, 6941), and four other units were stored at North Platte (6908, 6929, 6943, 6945).

The hope that the units would be saved from the scrap line was graphically shown by an urban artist in Salt Lake City when he used spray paint to ask Union Pacific, on several highway viaduct pillars near UP's North Yard, to "Save the Whales, Save the 6900s". Of the 47 Union Pacific 6900 class DDA40Xs built, 14 units are known to still exist. Twelve units have been officially preserved. A 13th unit, or rather the hulk of a 13th unit, sits forlornly in Chamberlain, South Dakota, on the Dakota Southern Railroad, without its engines, alternators, and traction motors. The 14th unit, UP 6936, remains in service.

(Read more about how UP 6936 was saved as part of the Heritage Fleet)

Preserved UP Centennial Units

(13 units)

  1. UP 6900 was donated to City of Omaha, Nebraska in September 1985, delivered in November 1986; moved in April 1988 east of Omaha Shops to Kenefick Park where it is on display with Big Boy 4023; the site was donated by Union Pacific to the City of Omaha for permanent exhibition; UP 4023 and UP 6900 were moved in May 2001 to make way for a new convention center, and were moved to temporary storage near the Durham Western Heritage Museum at Union Station in Omaha pending preparation of a new display site; moved to Mid America Car in Kansas City in January 2005 to be repainted; moved on April 15, 2005 to Lauritsen Gardens on a bluff overlooking Interstate 80; the display was completed and opened to the public on December 1, 2005.
  2. UP 6901 was donated to City of Pocatello, Idaho in October 1985, delivered on November 26, 1985, moved to Ross Park for display in March 1986.
  3. UP 6911 was donated to Technological Museum of the Federal Electricity Commission (Mutec) in Mexico City, in March 1985.
  4. UP 6913 was donated to the State of Texas in September 1985, delivered on March 10, 1986; displayed at Texas State Fairgrounds, Dallas, Texas
  5. UP 6915 was donated on May 12, 1985 to Southern California Chapter of the Railway & Locomotive Historical Society, Pomona, California; delivered during July 1985; moved to Los Angeles County Fairgrounds, Pomona, California, on July 28, 1987
  6. UP 6916 was donated to Ogden Union Station, Ogden, Utah in October 1985, delivered in January 1986.
  7. UP 6922 was reconditioned and used on a Rocky Mountain Railroad Club excursion special between Denver and Speer, Wyoming over the 1984 Memorial Day weekend; displayed at Coffeyville, Kansas, in late June 1984 and used in dedication of the new Jenks Shops in North Little Rock, Arkansas on July 14, 1984; used on a Intermountain Chapter NRHS excursion special between Denver and Speer, Wyoming on October 19, 1984; donated to City of North Platte, Nebraska on June 23, 1985, delivered in August 1985; displayed at Cody Park; officially dedicated on October 10, 1985.
  8. UP 6925 was sold to Dakota Southern Railroad, Wagner, South Dakota on April 20, 1987, stored at Chamberlain, South Dakota; empty shell, with engines, generators, air compressors and traction motors missing; not officially preserved; still there in mid-January 2015.
  9. UP 6930 was donated to Smoky Hill Railway & Historical Society, Shawnee Mission, Kansas, June 21, 1985, delivered August 1985; traded to Illinois Railway Museum in exchange for former Wabash coaches; UP 6930 was shipped from Kansas City to Chicago on October 31, 1991.
  10. UP 6936 is the last operating UP DDA40X, still in service, used for special trains. (Read more about UP 6936 as part of the Herritage Fleet)
  11. UP 6938 was donated during 1985 to Steamtown USA, Scranton, Pennsylvania; ownership of unit returned to UP in December 1988 following takeover of Steamtown by National Park Service (UP 6938 never left UP property); stored at North Little Rock, Arkansas until cosmetically restored and placed on display at Jenks Shops, North Little Rock, Arkansas in November 1989.
  12. UP 6944 was donated to National Museum of Transportation, St. Louis, Missouri on August 14, 1984; moved in October 2014 to Norfolk Southern's Juniata Shops at Altoona, Pennsylvania, for cosmetic restoration, completed in mid May 2015 and returned to St. Louis (includes incorrect 60-inch Union Pacific medallions; should not have the word 'Railroad' on the medallion)
  13. UP 6946 was donated to Feather River Rail Society in July 1984, delivered on August 20, 1984; unit was cosmetically restored, but stripped of usable parts by UP.

UP 6925 at Chamberlain, South Dakota

UP DDA40X 6925 was sold to Dakota Southern Railroad, Wagner, South Dakota on April 20, 1987, stored at Chamberlain, South Dakota; empty shell, with engines, generators, air compressors and traction motors missing; not officially preserved; still there in mid September 2022.

"6925, ex-Union Pacific DDA40X. Currently a hollow shell. When we bought it, the original Diesels had been replaced with drop-in 16-645E3B's out of SD-40-2's. Both had thrown rods. There were no traction motors. Lots of parts for our SD's, which the MILW had equipped with 645 power packs. We helped ourselves to parts as we needed them. One day Morrison-Knudsen called, looking for heavy block 645's as rebuild cores for the commuter units they were building. At the time heavy blocks were very hard to find. They made us an offer we couldn't refuse. Later, we sold the AR-12 alternators to National Railway Equipment. It was never our intent to run the DDA40X on the line west of Mitchell. At the time the 6925 was sold, a scrapper bought the 6906. We did acquire one truck frame from the scrapper, as that is the nearly irreplaceable part on a Centennial. The UP broke a couple of truck frames by dropping the second and third axles and not bolting the pedestal tie bars back on before supporting the weight on the first and fourth axles." (Alex Huff, email dated January 7, 2003)

The AR-12 alternators have a higher capacity than the EMD standard AR-10 alternator, and NRE installed them as part of their stationary engine test cells to test newly rebuilt diesel engines.

"The shell of the 6925 is still here in Chamberlain. When DSRC purchased the unit it had already been prepped by UP for trade-in. There were no traction motors or air compressors and the original prime movers had been removed. To qualify as trade in material, as I understand it, the unit had to have prime movers, so UP had dropped a pair of heavy block 645E3B's out of (I assume) SD40-2's. Both engines had thrown rods. We bought the unit as a parts source at approximately its scrap value based on weight. Our two SD7's and SD-9 had all been upgraded with 567C engines with 645 power packs by the MILW. It was also a bit of a lark, we didn't bid much for it. After we were notified we had won the bid, my brother and I decided to buy a spare truck frame from the 6906, on the slight chance that the 6925 would ever be put back into service and knowing that the trucks were as near as an irreplaceable part on the unit and that further UP had cracked a couple when someone didn't follow maintenance instructions and tried to support a unit on the first and fourth axles. At present, the prime movers are gone, sold to MK for cores for rebuilding for commuter locomotives at a time when heavy block 645's were very hard to find. The AR-12 alternators were sold to NRE for load testing rebuilt prime movers. Should the locomotive be rebuilt, I envision a couple of cheap (again?) SD40-2's donating the necessary guts, leaving two spare traction motors. I doubt that we will do it, but it won't be scrapped. Ed Bowers would probably drive a stake through my heart if I did. I get an occasional inquiry as to whether it is for sale from the locomotive collecting fraternity as it is the only one in private hands." (Alex Huff, email dated December 1, 2005)

"The rumor that DSRC bought the unit as a fuel storage tank was a poor joke I made to our primary mechanic and it was overheard by someone else who didn't know any better." (Alex Huff, message posted to Trainorders.com on December 30, 2018)

"It was actually bought for its 645 parts as the two bad-order prime movers had fifteen reusable power assemblies which we could have swapped into our ex-MILW SD's with 16-567C blocks which had been upgraded with 645 power assemblies. It was a pleasant surprise when we discovered the bad-order engines were not original but drop-in  heavy-block 645's, probably from SD40's." (Alex Huff, message posted to Trainorders.com on May 23, 2016)

The Dakota Southern Railway, and its operating rights over the railroad owned by the State of South Dakota, was sold to Rail Materials Salvage, Inc. (Michael Wayne Williams, co-owner with his wife and other asscoiates) in October 2009. The spare DDA40X truck was mistakenly cut up and sold for its scrap value. The DDA40X 6925 remained in private ownership, stored on Dakota Southern tracks. As of July 2021 UP 6925 was reported as "heading for a rail museum in Nebraska."

Rail Materials Salvage also owned the former C&NW line between Fremont and Hooper, Nebraska. Williams had purchased the line from the Nebraska Railroad Museum (operating the line as the Fremont and Elkhorn Valley Railroad), along with several pieces of railroad equipment. Williams renamed the line as the Fremont Northern, with plans of operating a dinner train, using the equipment purchased from the Nebraska Railroad Museum, retaining operating rights over the former C&NW branch. As the owner of the railroad (leasing it to the museum), Williams was obligated to maining the track in a safe condition. To end that obligation (and the operating lease), Williams traded the railroad equipment back to the museum, which then had to find a new home, allowing Williams to scrap the former C&NW branch that had been known since 1985 as the Fremont and Elkhorn Valley Railroad.

The Dakota Southern Railway (DSRC) owned the operating rights over the railroad owned by the State of South Dakota. Those operating rights, and some equipment (not including UP 6925) was sold by Williams on May 25, 2021 to the Ringneck & Western Railroad (RWRR), a subsidiary of Watco, operating over 108 miles of former Dakota Southern Railway track between Mitchell and Presho, South Dakota. The railroad was formed after Watco purchased the 189.7 miles of track between Mitchell and Kadoka, South Dakota from the state of South Dakota in 2021. The line beyond Presho is out of service with the US Hwy 83 crossing having been removed in the early 2000s during the years that the line was used only for car storage beyond Mitchell.

UP 6925 was reported as being donated to the Nebraska Railroad Museum at Nebraska City, Nebraska. The museum was organized by the Eastern Nebraska Chapter of National Railway Historical Society, with plans to locate their museum on property donated to them in 2020 by BNSF. The museum needed a new home after losing their lease and running rights over Williams' line between Fremont and Hooper, Nebraska. As of October 2022 the City of Nebraska City was contesting the donation by BNSF and the collection was sold to other parties to recover costs. UP 6925 was sold to Mike Roberts of Railroad Service Contractors in Kansas City.

As of mid September 2022, photos posted online show that UP 6925 was still sitting in Chamberlain, South Dakota. At the same time, inspection of the locomotive found that the persistant rumors of a cracked truck frame have always been false.

(Read the news item from October 24, 2022 about UP 6925, from Railfan & Railroad magazine)

Roster Listing

Full roster listing of the 6900 class locomotives.

More Information

"Union Pacific's DDA40X Centennial Locomotives", The Streamliner, Volume 21, Number 1, Winter 2007)

Selected Sources

D. S. Neuhart, Speech to the Annual Meeting of the Locomotive Maintenance Officer's Association, Chicago, Illinois, September 15, 1969.

Jerry T. Moyers and Jim Boyd, "Last of the Giants", Railfan, Volume 1, Number 4, Fall 1975, pp. 38-45

News items in various issues in 1969 to 1985 of CTC Board, Extra 2200 South, Pacific News, Pacific Rail News, The Mixed Train, plus messages posted to numerous internet discussion groups between 1995 and 2002.

Emails from Dave Krumenacker on January 15, 2003 and April 26, 2003.