DDA40

The DDA40 is a model designation, most prominently associated with a series of early diesel-electric locomotives. Specifically, it refers to the DDA40X, also known as the Centennial, a type of articulated locomotive built by the Electro-Motive Division (EMD) of General Motors for the Union Pacific Railroad. Thirty-two of these locomotives were constructed in 1969 and 1970 to commemorate the Union Pacific's 100th anniversary of the completion of the First Transcontinental Railroad.

The DDA40X was the most powerful single-unit diesel locomotive ever built at the time of its introduction. It featured two 16-cylinder EMD 645 diesel engines, each producing 3,300 horsepower, for a combined total of 6,600 horsepower. This immense power was delivered through 16 traction motors, allowing for exceptional hauling capabilities, particularly on heavy freight trains traversing mountainous terrain. Its distinctive features included a long car body housing the two engines and associated equipment, and a unique walkway configuration.

These locomotives were primarily used in high-density freight service, often pulling solid trains of coal or manifest freight. Their significant fuel consumption and maintenance requirements, however, contributed to their relatively short operational lifespan. While some were later rebuilt or modified, most DDA40X units were retired by the late 1980s. A few have been preserved for historical purposes, serving as a testament to a significant chapter in American railroad engineering and power.