I think the reason it's called a Zug is that when troops are marching in column, it's a bit like a train. Also in English, we have the word "baggage train".I am conversational in German but in this game, I picked up that Zug is also a platoon. But in my mind, I still read train, in that case, it must be written with a capital because it is a noun.
In Australia, we have a road train. It is a long combination vehicle consisting of two or more trailers. Zug is related to the English tug, Dutch tuig like voertuig,vliegtuig respectively, vehicle and airplane. I am after all Dutch-born and Germanic languages are all related. Don't use the Dutch 'tuig' by itself it means a rabble.Also in English, we have the word "baggage train".