The east-coast war channels were rebuilt from First World War practice, protected by mine barriers and coordinated with naval escorts, local defense flotillas, shore batteries, observers, and the RAF. Convoys began almost immediately in September 1939, yet some masters continued sailing independently and accepted greater risk. The routing problem illustrates how mines could protect shipping corridors while also imposing strict navigational constraints.
Notable Point · 1:04:15-1:07:16
War channels balanced mines, submarines, and navigation
Britain's marked and swept coastal routes had to be deep and wide enough for shipping while remaining shallow enough to restrict submarine attacks.