344 



INTRODUCTION 



tacking vessel off the beam of the submarine is im- 

 portant in reducing the maximum range at which the 

 enemy vessel can detect an echo from it. It should 

 also be useful for submariners to know under what 

 conditions a submarine is most vulnerable to contact 

 by echo ranging, that is, in what position, at what 

 aspect, or depth, or speed. In addition, any counter- 

 measures designed to reduce the probability of con- 

 tact, such as by making the submarine a less effective 

 acoustic reflector, require a quantitative knowledge 

 of the reflecting characteristics of the submarine. 



Similarly, such knowledge would be useful to anti- 

 submarine vessels in suggesting searching or attack- 

 ing operations. It is also required for the efficient 

 design and operation of many underwater echo-rang- 

 ing devices, such as certain decoys or mines. Informa- 

 tion on how much sound mines will reflect is impor- 

 tant both in the design of mine detection gear and 

 in the evaluation of echo-ranging equipment tests 

 carried out with a particular type of mine. 



This report emphasizes how submarines and sur- 

 face vessels reflect sound under field conditions. 

 Chapter 19 introduces the concept of target strength, 

 defines it in terms of quantities directly measurable, 

 and derives an expression for the target strength of 

 a perfectly reflecting sphere on the basis of ray 

 acoustics. Chapter 20 presents the theoretical back- 

 ground of reflection and scattering of sound from 

 bodies of various shapes on the basis of wave 

 acoustics, and reviews the theoretical calculations of 

 the target strength of a submarine. The technique of 

 the direct, field measurements of submarine target 

 strengths are described in Chapter 21, the indirect 

 measurements in Chapter 22, and all the results of 

 submarine target strength measurements are sum- 

 marized and discussed in Chapter 23. Finally, Chap- 

 ter 24 comprises all available information on surface 

 vessel target strengths and Chapter 25 summarizes 

 briefly the reflection of sound from both submarines 

 and surface vessels. 



