21. The active sonar used in such operations is often of " mid-frequency ", approximately 3.5 kHz. 22. These large " active sonars " are used to search for submarines and are very powerful. 23. Passive detection is almost impossible and surface units are forced to use active sonar to search. 24. Modern military submarines rely almost entirely on a suite of passive and active sonars to locate targets. 25. Once at close range the Spearfish uses active sonar to classify and home in on its target. 26. The primary tactical active sonar of a submarine is usually in the bow, covered with a protective dome. 27. Unlike active sonar , passive sonar does not emit its own signal, which is an advantage for military vessels. 28. Active sonar relies on an audible " ping " to generate echoes to reveal objects around the submarine.29. The coauthor of the interim report stated that animals killed by active sonar of some Navy ships were injured. 30. It is a Low Frequency Active Sonar ( LFAS ) and consists of both active and passive sonar arrays.
