SUBMARINE SIGNALS
Then there are submarine signals to tell of near-by vessels or shores. This signal arrangement includes a small tank on either side of the vessel, just below the water line. Within each is a microphone with wires leading to the bridge. If the vessel is near any other or approaching shore, the sounds; conveyed through the water from the distant object are heard through the receiver of the microphone. These arrangements are called the ship's ears, and whether the sounds come from one side of the vessel or the other, the officers can tell the location of the shore or ship near by. If both ears record, the object is ahead.