Submarines use sonar in order to steer around obstacles and avoid hitting fish and other submarines.
A sonar device sends a narrow beam of sound into the water. Auxiliary coastguard and Drumnadrochit businessman George Edwards detected a cavern 812 feet deep in Loch Ness. He believes this cavern may lead to a network of caves where Nessie and her family could live out of sight of most detecting devices. The picture above shows the sonar image of this cavern, now known as Edwards' Deep.