Why coastal shipping rivaled the railways in importance

Was Britain's coastal shipping as important as its domestic railways during the Second World War?

It was at least as important, and perhaps more so, because ships distributed imports among ports that neither the railways nor the limited road-haulage system could handle alone.

Ocean convoys could deliver a ship to Britain without placing its cargo near the final consumer. Unloading every arrival at Liverpool or another major port would overwhelm dock capacity and then transfer an impossible volume onto railways and a road network with relatively few heavy lorries. Coastal convoys kept the cargo aboard ship and moved it to a port nearer its destination, functioning as the local stage after the transatlantic journey.