One of Union Pacific's Centennial locomotives is display at the Museum of Transportation St. Louis Missouri.
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Overview
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 Big Blow 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, with 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.