Sea lanes could be mined and attacked, even if they could not be blown up like roads or railway lines. Britain's roads lacked modern carrying capacity, and the railway network was already working near its peacetime limit before new wartime demands arrived. Coastal shipping served a distributed port system, with supplies landing around the country and moving into nearby regions. Losing that traffic would overload inland transport and disrupt the national economy. Protecting local convoys was central to Britain's war effort.
Notable Point · 3:46-5:08
Why coastal convoys mattered to Britain
Britain's coastal shipping network connected many ports and supply destinations, making it a wartime logistics system that could not simply be replaced by road or rail.