A small stream may let troops cross on foot, while a large navigable river presents a much greater obstacle. Its width requires craft to carry the force across. Gunboats provide firepower to support those exposed movements. The same river that carries goods and military supplies along its course therefore creates a separate requirement for protected movement between its banks.
Notable Point · 1:27:11-1:29:47
Why navigable rivers demand crossing craft and gunfire
Large navigable rivers support transport along their length but require boats and supporting gunfire to move troops across.