44 MARINE SCIENCE 



During World War II, largely through funds supplied by the 

 Office of Scientific Kesearch and Development, rapid progress was 

 made in explaining the behavior of sound gear to the operating forces 

 in the Navy and also in designing equipments that could hope to over- 

 come some of the environmental factors. We had particularly good 

 luck in the prosubmarine applications. 



During the war period. Dr. W. M. Ewing realized that the ocean 

 was relatively transparent to low frequency sound and that there 

 existed within the ocean favorable paths by which low frequency ener- 

 gy could be transmitted over very long distances. Various means 

 of exploitmg these favorable characteristics of the medium have been 

 vigorously exploited by the Navy ever since. 



A very recent event which is unclassified will serve to emphasize 

 this point. Within the past few months hydrophones on the bottom 

 of Bermuda have picked up signals from the research vessel Vema 

 that were made near Australia and also in the Indian Ocean. Thus, 

 the permanent sound channel at mid- depths has been shown to pro- 

 vide for reliable acoustical concununication over distances of many 

 thousands of miles. 



In other words, we have transmitted acoustical signals past the 

 end of Africa. This is a rather better form of communication than 

 radio signals. 



Senator Engle. Let's understand that. Do you mean to say they 

 broadcast a signal near Australia ? 



Mr. IsEUN. They were near Australia and the people at Bermuda 

 heard it. 



Senator Engle. In order to do that, it had to go around the conti- 

 nent because of separation by land masses ? 



Mr. IsELiJsr. There is a permanent sound channel that exists nearly 

 everywhere in the ocean. It acts like a speaking tube and when you 

 use it right, you can transmit low frequency signals over great dis- 

 tances. 



We have known for 15 years that we could do this back and forth 

 across one ocean but what we haven't known is that we could signal 

 from one ocean to another. 



Senator Engle. And that is a level in the ocean ? 



Mr. IsELiN. Yes. 



The Chairman. But subject to change at times. That is what we 

 want to find out. Is it a permanent window or is it moving around ? 



Mr. IsELiN. This business of the coherence of the signal and so on 

 are perhaps things I shouldn't be talking about, but a lot is known 

 about this now and the whole subject has been going ahead at a very 

 satisfactory rate. The significant thing I want to emphasize here is 

 that this was not developed by statisticians but by people doing basic 

 oceanographic research. 



It is hardly an exaggeration to state that most of the modem sub- 

 marine-detection systems stem from concepts put forward by Dr. 

 Ewing and his collaborators now nearly 20 years ago, and the fact 

 that Dr. Ewing had the opportunity to take his particular kind of 

 science to sea has gained us a great many years' advantage over other 

 people. 



Amphibious warfare is another area in which oceanography made 

 important contributions during World War 11. Under the leader- 



