How do submarines use sonar?

Answer 1

Yes, submarines use sonar. At least all the military ones do, and a number of research submarines use it as well. One way to look at sonar is by dividing it into two basic types: active and passive. Let's look at each one and the uses should become plain. Active sonar is the generation of a "ping" or sonic signal and the transmission through the water of that signal. Sonar equipment then listens to any return echo and plots something that is (hopefully) useful in determining what may be there and how far away it is. Military submarines have this equipment, but rarely use it actively. Passive sonar is the use of the reveivers to listen to what sounds may be in the water to determine what may be out there and how far away it is. This is what is "the norm" for the boats. They slide through the dark water "listening their way" along. Active sonar uses a transmitted ping and listens to the echo, and the ping can be heard by others much farther away than the equipment can actually be used to resolve a contact. Other submarines (and other military listening equipment on ships, aircraft or affixed to the ocean floor) can hear the active ping and can then know that another submarine is out there and can locate it. A crude analogy might be a security guard looking for someone in a large, dark, container filled warehouse using a flashlight. The individual avoiding the guard could see the light and know where the guard was and could avoid him fairly easily without the guard really having a good chance of finding him. The use of active sonar by a (military) submarine is akin to this, and the boats don't go active with the sonar except once in a great while to test it. Submarines don't use active sonar to avoid underwater obstacles because they operate in water that is so deep that it is effectively "bottomless" to the boat.