In North American railroading, a cow-calf set is a pair of switcher-type diesel locomotives: one (the cow) equipped with a driving cab, and the other (the calf) without. The two are coupled together (either with regular couplers or a semi-permanent drawbar) and are connected with MU cables and brake lines so that both locomotive units can be operated by a single cab. Cow-calf sets were used in heavy switching, hump yard switching, and transfer runs between yards. Cows are analogous to A units an… (More on Cow-calf)