(a) SONAR stands for sound navigation and ranging. It is a technology that uses ultrasonic sound waves to detect and locate objects under water.
(b) Principle of SONAR is when ultrasonic waves are sent in sea water in all directions from the ship then these waves are received after reflection from an obstacle such as an enemy submarine, iceberg, sunken ship, etc. so to find the distance of the obstacle from the ship, the time interval between the instant when waves are sent and the instant when the waves are received, after reflection from the obstacle is measured.