apparatus for locating sources of sound in water , including a hydrophone system which is suspended from a buoy after being dropped into the water and whose one given reference axis is automatically aligned with the magnetic field of the earth by mechanically coupling the hydrophone system with a compass magnet . the hydrophones of the hydrophone system are electrically connected with a switching or control box by means of transmission wires which are insulated with an elastic plastic and pass freely through the water and the hydrophone system is mechanically fastened to the switching box to be rotatable in a recoilless manner about an axis which is perpendicular to the surface of the earth . the control box is in turn connected to the buoy by means of an elastic suspending cable and an electrical connecting cable .