11. The vessels are fitted with a C-Tech CMAS 36 / 39 hull-mounted high-frequency active sonar . 12. When they go to active sonar , it attracts the attention of the wandering Moby Dick. 13. Active sonar emits a sound wave and detects echoes from the hulls of other vessels.14. Active sonar creates a echo ) of the pulse.15. Active sonar is mainly used for under ice operations.16. The ships also have active sonar , radiological detectors, laser detectors and detector for radar irradiate. 17. A submarine usually relies on passive detection, not risking active sonar or a periscope observation. 18. Active sonar uses the reflection of sound emitted from the search equipment to detect submarines.19. For analogous reasons active sonar needs to transmit in a narrow beam to minimise scattering. 20. For ASW the inner screen needs good active sonar .
