Active sonar is a technology used to detect objects underwater by emitting sound waves. A sonar system sends out a pulse of sound, which travels through the water and bounces off objects, such as submarines or schools of fish. The system then listens for the returning echoes to determine the distance and size of the objects. This method is commonly used by naval forces for submarine detection and by fishermen to locate schools of fish. Active sonar can provide real-time information about the underwater environment, making it a valuable tool for navigation and exploration in marine settings.