Lord West tells the story of the Royal Navy during the Second World War, from early fights in Norway to the Battle of the Atlantic. And he shows how the Royal Navy saved Britain from invasion during the Second World War. In a chilly fjord in northern Norway he explains how a battle in April 1940 helped saved Britain from invasion later that summer, while in northern France he looks out from the top of a Nazi-era submarine pen and imagines how the prospects envisaged by the German U-boat aces must have changed during the course of the war. Producer: Giles Edwards.