INTRODUCTION TO SONAR 



RELATIVE BEARING 

 (OFSUBMARINE) 



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090° 

 ...1. 



TARGET ANGLE ASPECT OOPPLER 



PORT BEAM 



i 



DESTROYER 



STARBOARD 

 QUARTER 



SUBMARINE 



DOWN 

 FROM 

 SHIP 



SLIGHT 

 DOWN 



FROM S/M 



71.9 

 Figure 3-14. — Target angle. 



or five transmissions, based on doppler and 

 the first indication of bearing drift. Target 

 angle, on the other hand, is derived from more 

 precise data. It is necessary to knov/ the sub- 

 marine's course, which can be determined only 

 by tracking the submarine for several minutes. 

 In many attacks, it is difficult to report an 

 accurate target angle because of radical maneu- 

 vers by the submarine or because of insufficient 

 time to determine tai'get angle. In such in- 

 stances, target aspect information necessarily 

 must suffice for the conning officer to estimate 

 the target angle and adjust the attack lead 

 accordingly. 



In antisubmarine warfare, there is little time 

 between detection and attack. Target aspect thus 

 affords a means of reporting reliable informa- 

 tion quickly. 



Aboard a submarine, target angle is derived 

 by a method known as angle on the bow (Ab). 

 Whereas the ship uses 360° for computing target 



angle, the submarine uses only 180°, specifying 

 port or starboard side. To illustrate, a destroyer 

 has a submarine bearing 070°R. Aboard the 

 submarine the target angle would be reported 

 as "Angle on the bow, starboard 70." A rela- 

 tive bearing of 345° from ship to target is 

 reported on the submarine as "Angle on the 

 bow, port 15." Figure 3-14 illustrates some 

 angles on the bow. 



Target angle is not all guesswork. It can be 

 computed accurately by using the formula: target 

 angle equals true bearing plus 180° minus target 

 course. Expressed in fire control symbols, the 

 formula reads: Bts = By + 180 - C, where— 



Bts = target angle. 

 By = true bearing. 

 C = target course. 



Assume that you are on a ship and tracking 

 a submarine bearing 270°, course 135°. Find 

 the target angle by applying the preceding for- 

 mula. Thus: 



Bts = 270° + 180° 

 Bts = 450° - 135° 

 Bts = 315° 



135° 



An example of computing this target angle is 

 seen in figure 3-15. In effect, the +180° in the 

 formula allows the viewer to change places so 

 ;hat he may see his own relative bearing from 

 the target. Compare the relative bearing of the 

 destroyer from the submarine with the value 

 computed for target angle. 



If the product of By + 180° is less than target 

 course, 360° must be added to the equation before 

 subtracting target course. Example: A target 

 is on course 270°, bearing 010°. 



Bts = 010° + 180° 

 Bts = 190° + 360° 

 Bts = 550° - 270° 

 Bts = 280° 



Angle on the bow (Ab) may be computed in 

 the same manner as target angle, with one 

 exception. Because the answer is in degrees 

 of relative bearing, it must be converted to 

 degrees port or starboard. Referring again to 

 figure 3-15, you see that the destroyer bears 

 090°T and is on course 240°. 



Ab = 090° + 180° - 240° 



Ab = 270° - 240° 



Ab = 030° or starboard 30. 



If the answer is greater than 180°, subtract 

 the answer from 360° to obtain angle on the 

 bow to port. 



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