INTRODUCTION TO SONAR 



from the assist ship, as determined by the com- 

 puting ship, is expressed B + pn{B) = {B)pn, where 

 B equals relative target bearing from the com- 

 puting ship, pn{B) is the correction to be made 

 to account for displacement between the two 

 ships, and (B)pn equals relative tairget bearing 

 from the assist ship after correction is made 

 for displacement between the computing ship 

 and the assisting ship. 



Another type of parallax correction is Pdo, 

 which accounts for displacement of the weapon 

 launcher from the reference point (the sonar 

 transducer), measured in the deck plane along 

 own ship's centerline. 



system compatible with future weapons. One 

 modern fire control system may be used with 

 several weapon types. Regardless of the system, 

 it serves only one purpose: the destruction of 

 enemy submarines. 



After target position is determined the basic 

 problem for the system is to predict future 

 target position, calculate the required attack 

 course and firing tims, and transmit the data 

 to weapons and control stations. 



Because most underwater fire control systems 

 are of a classified nature, they cannot be included 

 in this text. Certain concepts are discussed, 

 however, to give you some basic knowledge of 

 how a fire control system operates. 



EQUIPMENT 



An underwater fire control system usually 

 is designed to operate with a particular weapon 

 system, although efforts are made to make the 



BASIC COMPUTING MECHANISMS 



The purpose of the computer in a fire control 

 system is to solve the problem of delivering a 

 weapon on the target. Available information is 



INPUT gear] 



END GEAR I 



SPIDER GEAR 



OUTPUT GEAR 



BALL BEARING 



BALL BEARING 



SPIDER SHAFT 



12.87 

 Figure 7-4. — Bevel gear differential. 



118 



