I passed the model shop in Dorking last night. In the window there's a huge model of a German rail-mounted gun. This beast runs on two parallel standard-gauge railway tracks and, even more remarkably (at least to me) it carries its own narrow gauge railway to bring the shells up to the position where they are loaded into the firing mechanism. Are there any other examples of rail vehicles that carried their own railway tracks? I'm aware of things like the Padarn Railway where 4ft gauge wagons carried twin pairs of 2ft-gauge lines to transport narrow-gauge wagons. Any others?