Mules (train)

Mules, when referring to trains, are a now largely obsolete method of assisting trains up steep grades. Historically, "mules" were small, powerful steam locomotives, typically used in pairs or multiple units, that were temporarily coupled to the front of heavier trains to provide extra tractive effort.

These locomotives would assist the train over a particularly difficult section of track, often a mountain pass or a sustained incline. Once the grade lessened, the mules would be detached and either return downgrade to assist another train, or continue on to a designated yard.

The term "mules" was likely derived from the animal of the same name, which were (and still are in some regions) known for their strength and sure-footedness in difficult terrain. Just as mules were used to haul heavy loads up steep slopes, these steam locomotives were employed for the same purpose on railroads.

The practice of using mules was common in the late 19th and early 20th centuries, particularly in areas with challenging topography. With the advent of more powerful locomotives and advancements in railway engineering, the need for mules gradually diminished. Electrification of railroads also played a significant role in phasing them out, as electric locomotives often possessed the necessary power to handle steep grades without assistance.

While the dedicated use of "mule" locomotives is rare today, the concept of adding extra motive power to a train for overcoming challenging terrain continues in various forms. Helper locomotives, often diesel or electric, are still employed in some locations, fulfilling a similar function to the historical "mules."