Great thread. I like those "cow and calf" units. What's the benefit in a "calf"? The traction power can get with a second unit, too. Wolfgang
A slug adds only tractive effort. A calf is just a switcher B-unit. Thus, it adds the horsepower as well. This allows the same train to move faster. Most cow-calf units were ordered for transfer service, unlike slugs which are often for hump service. The partly visible IHB unit is a slug.
