 Of French trade, 35 percent was with the British Empire and the majority of the tin, rubber, jute, wool and manganese used by France came from the British Empire.About 55 percent of overseas imports arrived in France via the Channel ports of Calais, Le Havre, Cherbourg, Boulogne, Dieppe, Saint-Malo and Dunkirk.Germany had to import most of its iron, rubber, oil, bauxite, copper and nickel, making naval blockade a devastating weapon against the German economy.