FOREWORD 



T'us VOLUME, together with Volumes 6, 7, and 9, 

 summarizes four years of research on underwater 

 sound phenomena. The purpose of this research was 

 to provide a firmer foundation for the most effective 

 design and use of sonar gear. It is generally true that 

 wide basic knowledge is an important element in en- 

 gineering practice. In the development of sonar gear, 

 knowledge of how sound is generated, transmitted, 

 reflected, received, and detected is clearly useful 

 both in the design of new equipment and in the most 

 eflScient utilization of existing gear. As a result of the 

 time delay between the design of new equipment and 

 its use in service, the most important application of 

 this basic information during World War II has been 

 in suggesting how existing equipment could best be 

 operated and tactically used. 



The importance of basic information on under- 

 water sound had been evident to both our own Navy 

 and the British for some time. Practical experience 

 had shown that the maximum distance at which a 

 target could be detected with underwater sound was 

 highly variable, even when the equipment was in 

 good operating condition. Since it was realized that 

 such variability might well be related to a variability 

 in oceanographic conditions, the Navy brought this 

 problem to the attention of the Woods Hole Oceano- 

 graphic Institution and the Scripps Institute of 

 Oceanography. To support an investigation, NDRC 

 contracted in 1940 with the former institution to 

 carry out studies and experimental investigations of 

 the structure of the superficial layer of the ocean and 

 its effect on the transmission of sonic and supersonic 

 vibrations. 



The work carried out under this contract, together 

 with supporting information obtained elsewhere, em- 

 phasized the relation of such basic factors to the 

 variable performance of sonar gear. Thus when some 

 months later it was proposed to establish a section in 

 NDRC to undertake research and development re- 

 lating to the detection of submerged submarines, 

 plans were made to increase substantially this re- 

 search effort. To this end, the plans which were for- 

 mulated by NDRC and approved by the Navy in- 

 cluded research on underwater sound phenomena at 

 the proposed laboratory at San Diego, to be operated 

 under a contract with the University of California 

 Division of War Research. This step not only in- 



creased the number of personnel engaged in this re- 

 search and facilitated study of oceanic conditions 

 peculiar to the Pacific area, but also most fortunately 

 made it possible for the San Diego Laboratory to 

 recruit certain of its staff from the Scripps Institution 

 of Oceanography and to draw upon the director and 

 staff of the Scripps Institution for very pertinent 

 background information in oceanography. While the 

 major source of the experimental data continued to 

 be the Woods Hole and San Diego Laboratories, very 

 pertinent data were from time to time obtained from 

 other laboratories, notably New London, Harvard, 

 the Massachusetts Institute of Technology, and the 

 Underwater Sound Reference Laboratories. 



Quite promptly, an analytical section, later known 

 as the Sonar Analysis Group, was organized under a 

 contract with Columbia University Division of War 

 Research. The function of this group was to assist in 

 the analyses of data being accumulated by Woods 

 Hole, San Diego, and other laboratories, and, as it 

 became possible to draw conclusions, to present these 

 to other groups interested in operations or design. In 

 this connection it should be emphasized that the 

 seeming importance of this research to the Navy led 

 to the assignment of naval personnel to follow the 

 work actively. In particular, officers of the Sonar De- 

 sign Section of the Bureau of Ships followed very 

 closely the research of this analytical group, partici- 

 pating directly in much of the work. 



The results obtained in this research and sum- 

 marized in this and companion volumes found many 

 important applications during World War II. The 

 rules used for operating sonar gear were based in part 

 on these results. Many tactical rules embodied in 

 submarine and antisubmarine doctrine were directly 

 based on information obtained in these basic studies 

 of transmission, reflection, detection, and the like. 

 As an example, the spacing between antisubmarine 

 vessels in different tactical and oceanographic condi- 

 tions was varied according to the measured tempera- 

 ture gradients in the upper layers of the ocean. In 

 addition, the choice of operating frequency, pulse 

 length, size, and power for new equipment, especially 

 for submarines, was considerably influenced by such 

 basic knowledge. It can be stated with considerable 

 confidence that a detailed basic knowledge of under- 

 water sound phenomena will be of increasing help in 



