The term UNDERWATER DETECTOR can be summarized as a device used to detect objects UNDERWATER, such as submarines or other vessels. The most common type of UNDERWATER DETECTOR is SONAR, which stands for Sound Navigation and Ranging. Sonar works by sending out sound waves and measuring the time it takes for them to bounce off an object and return to the source. This allows the user to determine the distance and direction of the object. Sonar is used in a variety of applications, including navigation, military operations, and scientific research.