Britain utterly depends on "British bottoms" to deliver food and materials from overseas. It's a huge import market. In World War I and World War II, German subs sought to cut off Britain from her lifeline to America and her dominions and colonies. World War II was especially close run in the early part of the war. The National Submarine Memorial commemorates the other side of the coin - the British submariner, who was an effective force in both stopping German U-boats and imperiling the North Sea to German trade, but also attacked Japan, who was unable to defend against submarine attack. Right-click and choose "view image" to enlarge.
Welcome to the Imperial War Museum The Imperial War Museum, the multi-branch national museum of war and wartime life from the First World War, through the Second World War, to the present day.