448 



INTRODUCTION 



with (1) air bubbles of widely varying size; (2) tur- 

 bulent motion in the sea, on a scale small compared 

 with the dimensions of ships; and (3) thermal in- 

 homogeneities or irregularities in the sea, also on a 

 small scale. 



Although the bubble theory of acoustic wakes now 

 enjoys general acceptance, it is difficult to put it to a 

 conclusive test; it has been adopted rather by de- 

 fault of the other two explanations. It would seem 

 logical, therefore, to begin by presenting the evi- 

 dence which shows that the turbulent and thermal 

 microstructure of the sea does not provide an ade- 

 quate explanation of the acoustic properties of wakes. 

 However, in order to simplify the exposition, it is pref- 

 erable to discuss first the physical mechanism of the 

 formation and dissolution of bubbles in Chapter 27 

 and their acoustic properties in Chapter 28, and to 

 defer the necessarily rather cursory treatment of the 

 temperature and velocity structure of the sea until 

 Chapter 29. The theoretical Chapters 27 to 29 com- 

 prise the delineation of the working hypothesis which 

 guides current wake research. Then the bulk of this 

 volume (Chapters 30 to 33) describes the technique 

 and the results of acoustic measurements made on 

 wakes. In Chapter 34, the experimental data are 

 interpreted in terms of the bubble theory; in other 

 words, a test of the working hypothesis is under- 

 taken. In the final Chapter 35, some conclusions 

 which should be relevant in practice are drawn from 

 the previous observations. Incomplete as the experi- 

 mental foundations of some of these conclusions are, 

 it appears useful to formulate some tentative general- 

 izations as to the geometry and acoustic properties of 

 wakes. Pending future research that may fill the con- 

 spicuous gaps in oui knowledge of wakes, such gen- 

 erahzations should answer at least some of the ques- 

 tions about wakes raised by the demands of naval 

 tactics. 



Figure 8. 

 feet. 



Wake of USS Saratoga (CVS) from 4,000 



