INTRODUCTION TO SONAR 



they are not considered effective as antisub- 

 marine weapons. These torpedoes are used chief- 

 ly against surface targets at fairly short ranges. 

 They are noisy and thus are detected easily 

 but are difficult to counter because of their 

 high speed. 



Acoustic homing torpedoes available to sub- 

 marines have features for homing passively, 

 actively, or a combination of the two. 



Wire-guided torpedoes are a variation of 

 the acoustic homing torpedo. They are guided 

 to the target submarine's vicinity by signals 

 sent over the wire by the launching submarine. 

 After the target is acquired by the torpedo, 

 it homes on the target without further guidance 

 from the launching submarine. 



The submarine also has a rocket-propelled 

 weapon, containing a nuclear warhead, called 

 SUBROC, which was described in chapter 2. 



DETECTION-TO-DESTRUCTION PHASES 



Theoretically, the fire control problem begins 

 when a target is detected and ends with its 

 destruction. In practice, though, the fire control 

 problem starts well after initial detection. It 

 commences after the initial classification and 

 when target tracking is ordered. 



Like all other fire control systems (anti- 

 aircraft, surface-to-surface, and the like), the 

 antisubmarine fire control system solves the 

 problem in the following stages: (1) tracking 

 the target; (2) analyzing target motion; and (3) 

 computing ballistic solution. 



Detecting a submarine is no easy matter. 

 Neither is it a simple task, once a submarine 

 contact is established, to carry out the succes- 

 sive phases mentioned here. Although fire control 

 systems are capable of performing complicated 

 tasks, such as predicting future positions, sub- 

 marine hunting is subject to errors caused by 

 human judgment. Training in proper operation 

 of the equipment for maximum ASW effectiveness 

 is a must for Sonar Technicians. 



Because the same equipment often is used in 

 detecting a submarine as in tracking it, detection 

 is considered as a phase, even though in the 

 strictest sense it may not be a part of the problem. 



Detection Phase 



A submarine may be detected in several ways, 

 the most positive being visual sighting. If the 

 submarine is seen to dive, classification is 

 evident; there is no question about the positive 

 nature of the contact. Once such a classification 



is established, the next phase (tracking) can be 

 initiated. 



Detection also can be made by radar. If a 

 radar contact suddenly disappears, there is a 

 good chance that the echo was the return from 

 a surfaced submarine and that the disappearance 

 was caused by diving. If sonar contact also is 

 held, it can be assumed the contact is a sub- 

 marine. Most surface-search radars can receive 

 a radar indication from a periscope. Hence, it 

 is possible to track a submarine that is operating 

 completely submerged except for its periscope. 

 The radar method goes hand-in-hand with visual 

 detection, because radar frequently provides the 

 first indication, directing eyes to the location 

 of the periscope, snorkel, sail, or hull of the 

 submarine. 



The sonar equipment aboard your ship or 

 submarine is designed to detect and track the 

 submarine, and feed computing devices with 

 tactical data to achieve the destruction phase 

 of the problem. 



Tracking Phase 



After detection, the contact must be tracked. 

 Aboard a submarine, a graphic display of target 

 bearings is made during this phase. From infor- 

 mation furnished by this display, target motion 

 is established. Normally, the submarine uses 

 only passive sonar for tracking, because active 

 sonar may disclose the presence and even the 

 location of the tracker. 



Shipboard Sonar Technicians track the target 

 with active sonar, depending largely upon the 

 strength and quality of the echo of the trans- 

 mitted pulse for target information. Antisub- 

 marine ships have fire control systems that 

 incorporate automatic tracking features. Once 

 the contact is established firmly, the automatic 

 devices keep the sonar on the target, and com- 

 pute the course to be steered so that the ship 

 will arrive at the best firing position for the 

 weapons selected for use. 



Basically, establishment of relative rates of 

 target motion is all that is desired from the 

 tracldng phase of the problem. The tracking 

 phase sets up the pattern for the next phase — 

 target motion analysis. It is from the relative 

 rates that actual target motion is determined. 



Target Motion Analysis Phase 



The target motion analysis phase is a dynamic 

 problem because both the attacking unit and the 

 target usually are in motion continuously, and all 



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