The ALCo Century 636 was the most powerful single-engine diesel-electric locomotive constructed by the American Locomotive Company (ALCo). It used their 251 prime mover. The locomotive had a C-C wheel arrangement and 3,600 horsepower (2,700 kW). The locomotive rode on a pair of trucks of all-new design, known as the Hi-Ad, standing for 'high adhesion'. Visually, it is similar to the Century 630, but can be distinguished by the intercooler box. The C630 has two grilles here, one above the other. The C636 only has the upper grille.