EMD DDA40X

The Electro Motive Division DDA40X (nicknamed "Centennial") is a 6,600 hp, twin-engine (consisting of two modified 3,300 hp 16-645E3A engines), eight-axle diesel locomotive built specially for the Union Pacific Railroad (UP) from 1969 to 1971. As of today, Centennial 6936 is the only operational member of the class and is used in both excursion service and occasional revenue freight service. On April 28, 2022, Union Pacific has donated 6936 to the Railroading Heritage of Midwest America (RRHMA), based in Silvis, IL.
==History==
The DDA40X was mainly built to haul long and heavy trains over the Sherman Hill on UP's Transcontinental route. They were built as part of the railroad's quest for ever more power per locomotive, replacing the much less fuel-efficient GE gas turbine electric locomotives. They were, essentially, an evolution of the earlier DD35 and DD35A, but with more modern feature sets like AC/DC conversion for the traction motors. Forty-seven were built in total, numbering from 6900 to 6946.
The "X" in the name stands for "experimental", and many systems were tested in the Centennials, including modular electronics used in the -2 models and later EMD products, an air raid style siren to indicate movement (this was not kept), and integrated load testing for the electronics. The wide cab was the same as the FP45/F45 cowl units, and lacked the increased structural bracing in modern "safety" cabs.
By 1980, they began to be withdrawn for storage for economic and repair reasons. An uptick in traffic in the early 1980s had twenty-five return to usage, but all were retired by 1985 in favor of smaller, cheaper to run locomotives (such as the SD60 and C40-8). Thirteen are preserved and the rest were scrapped. Only one, UP 6936, was mostly used in excursion service with the UP's heritage fleet, as well as occasional freight service.
On April 28, 2022, the UP announced that 6936, along with Challenger 3985, 2-10-2 type 5511, and other pieces of equipment from their heritage fleet, will be donated to the Railroading Heritage of Midwest America (RRHMA) in Silvis, IL. 6936 was towed by diesels out of Cheyenne, WY on November 11, 2022 alongside 3985 and 5511 and later arrived at the RRHMA's former Rock Island Railroad shops and yard in Silvis, IL on November 19, 2022. The RRHMA plans to use 6936 alongside 3985 and 5511 in excursion service.
==Stock list==
Image	No. 	Build date	Manufacturer 	Notes
 	6900	1969 	Electro-Motive Diesel	On static display at Kenefick Park in South Omaha, Nebraska along with Union Pacific Big Boy No. 4023.
 	6901	1969 	Electro-Motive Diesel	
 	6902	1969 	Electro-Motive Diesel	
 	6903	1969 	Electro-Motive Diesel	
 	6904	1969 	Electro-Motive Diesel	
 	6905	1969 	Electro-Motive Diesel	
 	6906	1969 	Electro-Motive Diesel	
 	6907	1969 	Electro-Motive Diesel	
 	6908	1969 	Electro-Motive Diesel	
 	6909	1969 	Electro-Motive Diesel	
 	6910	1969 	Electro-Motive Diesel	
 	6911	1969 	Electro-Motive Diesel	
 	6912	1969 	Electro-Motive Diesel	
 	6913	1969 	Electro-Motive Diesel	On static display at the Museum of the American Railroad in Frisco, Texas
 	6914	1969 	Electro-Motive Diesel	
 	6915	1969 	Electro-Motive Diesel	On static display at the RailGiants Train Museum in Pomona, California.
 	6916	1969 	Electro-Motive Diesel	On static display at the Utah State Railroad Museum in Ogden, Utah.
 	6917	1969 	Electro-Motive Diesel	
 	6918	1969 	Electro-Motive Diesel	
 	6919	1969 	Electro-Motive Diesel	
 	6920	1969 	Electro-Motive Diesel	
 	6921	1969 	Electro-Motive Diesel	
 	6922	1969 	Electro-Motive Diesel	On static display at the Cody Park Railroad Museum in North Platte, Nebraska along with Union Pacific Challenger No. 3977.
 	6923	1969 	Electro-Motive Diesel	
 	6924	1969 	Electro-Motive Diesel	
 	6925	1969 	Electro-Motive Diesel	
 	6926	1969 	Electro-Motive Diesel	
 	6927	1969 	Electro-Motive Diesel	
 	6928	1969 	Electro-Motive Diesel	
 	6929	1969 	Electro-Motive Diesel	
 	6930	1970 	Electro-Motive Diesel	On static display at the Illinois Railway Museum in Union, Illinois.
 	6931	1970 	Electro-Motive Diesel	
 	6932	1970 	Electro-Motive Diesel	
 	6933	1970 	Electro-Motive Diesel	
 	6934	1970 	Electro-Motive Diesel	
 	6935	1971 	Electro-Motive Diesel	
 	6936	1971 	Electro-Motive Diesel	Operated mainly in excursion service with the UP's steam excursion program from the 1980s to 2017. Donated to the Railroading Heritage of Midwest America (RRHMA) in Silvis, Illinois on April 28, 2022.
 	6937	1971 	Electro-Motive Diesel	
 	6938	1971 	Electro-Motive Diesel	Sits outside of the Jenks Jenks Locomotive Facility in North Little Rock, Arkansas.
 	6939	1971 	Electro-Motive Diesel	
 	6940	1971 	Electro-Motive Diesel	
 	6941	1971 	Electro-Motive Diesel	
 	6942	1971 	Electro-Motive Diesel	
 	6943	1971 	Electro-Motive Diesel	
 	6944	1971 	Electro-Motive Diesel	On static display at the National Museum of Transportation in St. Louis, Missouri.
 	6945	1971 	Electro-Motive Diesel	
 	6946	1971 	Electro-Motive Diesel	On static display at the Western Pacific Railroad Museum in Portola, California.
==Trivia== 
*The DDA40X is often referred to as the "Centennial" to celebrate the 100th anniversary of the completion of the Transcontinental Railroad.
*The DDA40X was one of the first types of EMD locomotives to have a "wide nose" before the official "safety-cab" era began in the 1990s.
* Several DDA40X locomotives are preserved, but 6936 is the only to still remain in service only to pull special passenger excursions and occasional freight trains.
*"DD" indicates the unit has two trucks, each with four powered axles, yet the EMD "DD" units are sometimes referred to by railfans as "Double Diesel".
*Large sandboxes were added to the sides of the DD35 and DDA40X above the rear trucks due to a flaw in the DD35's rear sand box, which developed cracks that fouled the electrical cabinets with microscopic sand particles.
*The four-axle trucks also required more sand than traditional three-axle trucks. Hence, the need for having large sandboxes mounted on the sides of the units.
*The first of the engines; 6900, currently resides at Kenefick Park in Omaha, NE, the current location of Union Pacific Big Boy locomotive 4023 as well as Union Pacific's corporate headquarters.
*The UP's renumbered fleet of GE AC6000CW units retain the same numbers that their giant DDA40X predecessors originally retained.
*A few 6900s, most notably 6918, had air raid sirens as grade crossing warnings.
*On November 30, 2000, 6936 collided with a dump truck at a railroad crossing in Livonia, LA, twenty miles north of New Orleans, LA. The collision killed both the dump truck driver and a UP employee inside the cab of the locomotive and the damage it sustained left it in danger of being retired from service due to the severity of the damage. Thankfully, it was eventually repaired and returned to service on May 2, 2001, complete with a few modifications.
*During its excursion service career with the UP's heritage fleet, 6936 reunited with three of its surviving sisters, those being 6900 in 2005, 6946 in 2007, and 6930 in 2013.
==Media==
*Image Gallery
*PicSearch
*VidSearch
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