PREFACE 



IN THE COURSE of prosubmarine and antisubmarine 

 research carried out during World War II, a large 

 amount of information was obtained on the propaga- 

 tion of underwater sound. Much of this was gathered 

 in fairly random ways, such as while testing under- 

 water sound equipment. Most of the useful informa- 

 tion, however, was obtained by groups devoted pri- 

 marily to the problem of underwater sound propaga- 

 tion. While valuable results had been found before 

 World War II by the Naval Research Laboratory, 

 the British, and other groups, most of the informa- 

 tion on underwater sound transmission obtained 

 during the war resulted from a program of studies 

 organized by Division 6 of the National Defense Re- 

 search Committee and carried out in collaboration 

 with Navy laboratories at San Diego and elsewhere. 



It should be kept in mind that these so-called 

 fundamental programs were not fundamental in the 

 usual scientific sense. They were not aimed at isolat- 

 ing and understanding the different factors at work, 

 but were designed rather for the accumulation of in- 

 formation which would be useful in antisubmarine 

 and prosubmarine operations. Thus effort was con- 

 centrated on the study of the transmission loss of 

 sound generated with standard sonar gear under 

 varying oceanographic conditions, rather than on a 

 detailed study of each of the individual factors af- 

 fecting underwater sound transmission. Similarly, 

 the reflection of sound from actual submarines was 

 studied rather than the individual mechanisms re- 

 sponsible for the origin of echoes from underwater 

 targets. 



During the war this approach was abundantly 

 justified by its results. The information obtained on 

 underwater sound propagation under different ocea- 

 nographic and tactical situations was immediately ap- 

 plied to the more effective use of existing underwater 

 sound equipment in different situations. The results 

 of transmission, reverberation and other studies were 

 usually used operationally much more rapidly than 

 the results of equipment development. 



Over a longer period, however, information on 

 underwater sound can be most useful if the phenom- 

 ena are not merely observed but also explained. An 

 understanding of each of the basic factors affecting 



underwater sound propagation would make it possi- 

 ble to predict the transmission and reflection to be 

 expected under conditions widely different from 

 those prevailing when the original measurements 

 were taken. While the primarily experimental re- 

 search carried out during the war could be immedi- 

 ately applied to the gear then in existence, the de- 

 velopment of new equipment for new and unforeseen 

 tactical situations requires an understanding of the 

 factors which influence underwater sound. The ulti- 

 mate aim of basic underwater sound research, espe- 

 cially during peacetime, should be to develop such 

 an understanding. 



The present volume presents the essential results 

 obtained in the studies of underwater sound up to 

 the middle of 1945. This volume was written pri- 

 marily from the fundamental viewpoint of scientific 

 research; in other words, the data are presented 

 against a framework of an attempted understanding 

 of the factors involved rather than as an unadorned 

 summary of the experimental results. Since the meas- 

 urements were not carried out primarily to increase 

 this understanding, this presentation of the subject 

 leads to many obvious gaps. However, it is hoped 

 that the overall scientific picture presented will be 

 stimulating to any future research workers in this 

 field. To aid those interested in application, practical 

 summaries of the results are given at the end of each 

 of the four parts comprising this volume. 



Since our understanding of the details of under- 

 water sound has not been sufficient in most cases to 

 allow an elaborate comparison between theory and 

 experiment, it has been possible in most of this volume 

 to write the text on the level of a senior engineering 

 student. A deliberate effort has been made to keep 

 to this level wherever possible in order to make the 

 results available to the widest possible group of 

 readers. However, more elaborate theoretical devel- 

 opments have been included where it was believed 

 that they were essential to an understanding of the 

 full significance of current information. 



The first two parts of this volume deal with the 

 propagation of sound in the absence of targets. Part I 

 discusses the transmission loss of sound sent out from 

 a projector, while Part II deals with sound which has 



