The term SUBMARINE DETECTOR is a job description for the use of SONAR (Sound Navigation and Ranging). Sonar is a technology that uses sound waves to detect objects underwater, such as submarines. It works by sending out sound waves and then listening for the echoes that bounce back from objects in the water. By measuring the time it takes for the sound waves to travel and return, the distance and direction of the object can be determined. Sonar is an important tool for military and commercial operations, allowing them to detect and track submarines and other underwater objects.