on the surface, it might be more than 200 feet deep and any- 

 where within a circle of more than 1.000-feet radius 



i> 



Also j with the searchlight-type of sonar which was 

 standard during most of World War II, the attacking vessel 

 was forced to make the last part of its run blindo The 

 sound beam of the attacking vessel travelled outward in a 

 generally horizontal direction Its vertical angle was 

 wide enough to detect a submarine submerged at considerable 

 depth s provided the range was great enough. But as the at- 

 tacking vessel bore down on the submarine s the angle of the 

 beam tended to pass over the submarine and contact was losto 

 Moreover, as the range was closed, the bearing changes re- 

 quired to keep the beam fixed on the submarine became so 

 rapid that the sonar operator was unable to keep his gear 

 properly trainedo 



Finally 9 there was the difficulty of personnel and 

 training. Since no single piece of equipment so far de- 

 veloped is adequate both to locate and destroy a submarine, 

 the coordination of equipment and crew is often more impor- 

 tant to success than the detailed perfection of the indivi- 

 dual elements. This is why the program of Division 6 laid 

 so much stress on the selection and training of personnel „ 



Need for Basic Information , 



These were some of the factors which made the underwater 

 sound program a difficult and challenging one and whichj, when 

 Division 5 (then Section C-4) of NDRC was organized^ high- 

 lighted the fact that lack of basic scientific information 

 was a serious obstacle to the design of more effective under- 

 water sound gear. For the intelligent development of such 

 gear, basic information was needed concerning such behavior- 

 isms of sound In water as the drop in intensity of underwater 

 sound that has travelled between two points in the oceanj the 

 influence on this intensity drop of refraction due to temper- 

 ature gradients and other qualities^ the amount, character 

 and masking properties of extraneous background noise ° and the 

 reflecting properties of targets. 



When NDRC first undertook basic research on the trans- 

 mission of underwater sound it turned naturally to the Woods 

 Hole Oceanographic Institution, Through continued contacts 

 with the Navy in the years before World War II the members of 

 the Woods Hole staff had acquired a realistic knowledge of 



23 



