Sound waves travel very well through water, so they are used to detect submarines or even shoals of fish. A sonar device under a ship sends out sound waves that travel down through the water. The sound waves are reflected back from any solid object they reach, such as a submarine, shoals of fish or the seabed. The echoes are received by the ship and can be used to ‘draw’ an image of the object, and its location, on a screen.
Picture credit: google
