river supply question

[Bacillus98]

Hello. It's my understanding that supply can be only traced over a bridge(either one in game or made by a engineer). So how does one get supply over a river in a sector of a front that does not have a bridge engineers? I have some engineers that can remove mines and have noticed if they are near a bridge, an unit can cross the river, but only in travel mode. However, you cannot trace supply across river. The scenario I am talking about in particular is the "6th Panzer Breakthrough" in M41. The german southern division can cross the Vop river eventually, but seemingly with no supply.