How does sonar work?
Sonar (SOund NAvigation and Ranging) gives our submarines virtual "eyes" underwater. Sonar is used primarily to detect ships and submarines. There are two types of sonar: active and passive. When using active sonar, a submarine transmits a pulse of sound into the water and listens for how long it takes to bounce off another object such as a ship or submarine and return. This gives information about that ship or submarine's direction and distance away. Unfortunately, if a submarine uses active sonar, all the other sonar-capable ships and submarines in the area would know that the submarine is there. Since the primary advantage that submarines enjoy is stealth (other ships don't know where they are), most submarines rarely use active sonar. Passive sonar listens for the sounds coming from other ships and submarines. When a submarine uses passive sonar, it is able to obtain information about other ships and submarines without revealing its own position. Like detectives examining a crime scene, skilled sonar operators can determine such things as ship speed, number of propellers and even the exact kind of ship just by listening to the sounds.
What does sonar sound like?
Active sonar makes sounds much like the "pings" you've probably heard on TV shows and in movies. Submarines usually don't use active sonar because after the first ping, the submarine is no longer covert. Instead, they use passive sonar. Passive sonar listens only and puts no noise in the water.
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