Chapter 7 — BASIC FIRE CONTROL 



r'c A 



Sx^rs^-3 SS.<£14^ 





2x. 



71.124 

 Figure 7-3. — Sonar position quantities. 



As shown in figure 7-3, quantity B is the target's 

 relative bearing at the time the echo is received. 

 Target depth (Rv) and horizontal range (Rh) 

 combine to produce actual target range (R). 



NAVIGATIONAL PARALLAX 



Two ships sometimes operate as a unit to 

 solve the underwater fire control problem. One 

 ship measures and computes position data and 

 transmits the information to its assist ship, 

 which makes the attacl^. When two ships operate 

 in this manner, correction for parallax must be 

 made. Correction for parallax must also be 



made when conducting a DASH attack. Parallax 

 is the apparent displacement of an object when 

 seen from two different points. 



The class of quantities used to express 

 linear displacement between the computing ship 

 and the assisting ship reference points is called 

 navigational parallax (symbolized Pn), and is 

 measured along the navigational parallax base- 

 line. 



Parallax corrections to a basic quantity, 

 to account for displacement, are symbolized 

 by lowercase letters pn, and precede or follow 

 the basic quantity, which is enclosed in paren- 

 theses. To illustrate: Relative target bearing 



117 



