Sonar

From Command and Conquer Wiki

SONAR (SOund NAvigation and Ranging) is a technique that uses sound waves to identify or detect objects. It's primary usage is in naval pursuits, as sound vibrations travel faster in water than in the air.

Passive sonar is the use of sensitive microphones to listen without transmiting. This type of detection is silent, and therefore impossible to intercept; but is costly and requires advanced components. Additionally, although it can accurately identify a target, it requires measurements and calculations to be done in order to identify the range, course, and speed, and silent targets themselves can be hard to detect. As it is silent, passive sonar is the preferred choice of submarines, which can pick up the sound of a surface vessel, identify an easy target from a difficult one, and sink it at their leisure.

Active sonar or echolocation functions like an undersea version of radar, substituting sound for radio waves. A "ping" is transmitted, which carries forward until it "bounces" off a solid object, back towards the transmitting one. This pinpoints the exact position of a target object. However, the "ping" is requisitely noisy and will be heard by the target object, and it cannot precisely identify the type of target. Also, the use of such systems is believed to potentially damage echolocating sea life, such as dolphins. However, it is extremely useful in detecting silent objects; making it a necessity for submarine hunting. Gunboats and Destroyers use active sonar to locate submerged subs.