During the 2nd World War the British Fleet was housed at Scapa Flow in the Orkneys. However, they were prone to attack from German Submarines. Boats were scuttled in the narrow straits between islands and torpedo nets were deployed but submarines still got through at high tide and sank a battle ship. Churchill ordered that causeways should be constructed to block the straits. These were controversially built using Italian POWs but solved the submarine problem. They became known as the Churchill Barriers and are now used as roads to connect the islands. The scuttled ships are still there and visible.