sound waves. And the sea has its full quota of perversities 

 to trouble the sound man, 



It was in the hope of determining the nature of these 

 limiting characteristics of sea water that, in 1936, the Sub- 

 marine Signal Company aroused the interest of the Woods Hole 

 Oceanographic Institution in the possibilities of an inves- 

 tigation. In January, 1937, a party of oceanographers and 

 sonar engineers went to the Caribbean to investigate the prob- 

 lems of sound propagation in an attempt to correlate the anom- 

 alies with oceanographic data. This research, which disclosed 

 the effect of thermal gradients on underwater sound transmis- 

 sion and which saw the first use of the bathythermograph for 

 measuring these gradients, laid the foundation for the broad 

 program of oceanographic research which Division 6 was to 

 undertake during World War II and which is discussed in a 

 later chapter. 



- 9 - 



