32 



OCEAN SCIENCES AND NATIONAL SECURITY 



Percentage of ocean 

 less than indicated 

 Depth in feet — Con. deplh 



15,000 60. 



18,000 90.0 



21,000 99.0 



24,000_. 99.5 



35,800 100.0 



These so-called deep sound channels have clear implications for 

 long-range, passive, acoustical detection of underwater objects. 



This phenomenon may serve to introduce the contention by those 

 interested in the sea that the most urgent reason for penetrating the 

 full depths is military. The sea conceals its contents. A stone 

 thrown into the water almost instantly disappears. In clear, un- 

 ruffled water, its trajectorj^ may be followed visibl}^ to depths of 

 perhaps ten or so feet, but then is lost from view. It is this opaque- 

 ness of water that gives the submarine its enormous advantage of 

 concealment, and the concomitant property of surprise. 



T.\BLK 1. — Depth of ocean versus expanse 



Percentage of ocean 

 less than indicated 

 Depth in feet: <*«?"» 



1,000 8.5 



2,000 10.5 



3,000 11.9 



6,000 15.9 



9,000 20.5 



12,000 34.5 



Source: Kossinna, Erwin. 1921. Die Tiefpn des Weltmeeres. Berlin Univ., Institut f. Meereskunde, 

 Veroff., N.F., A. Qeogr.-naturwiss. Reihe, Heft 9, 70 pp., 1921. 



Even with exceedingly sensitive devices to measure the sub's dis- 

 turbance of the Earth's magnetic field, detection from the surface 

 becomes more and more difficult as the craft dives deeper. It may 

 take a deep-diving sub to catch a deep-diving sub. 



Beginning in World War I, efforts to render the sea more trans- 

 parent were focused on the use of underwater acoustic devices, either 

 hydrophones to listen passively, or active devices which emit sharp 

 pings of sound and depend on echoes to reveal otherwise silent and oc- 

 culted targets. Such devices, attached to the underside of searching 

 surface ships, on killer subs, or dunked from blimps and helicopters, 

 all suffer from the same limitations — the relatively short range at 

 which sounds may be detected. Obviously, those situated near the 

 sea surface also suffer from the distracting effect of background noise 

 from the waves themselves. Nevertheless, the major effort today is 

 still concentrated on the use of underwater acoustics to detect, classify, 

 and track, and if necessary, control the weapons which will destroy a 

 hostile underwater boat. 



Nature itself, however, has conspired to defeat the success of some 

 of these systems. Sound propagating in the depths is reflected or 

 refracted when the sound waves strike the interface between two 

 layers of sea water at different temperatures and densities. Sub- 

 mariners have learned how to exploit this phenomenon so as to hide 

 their boats completely. Another aspect of this game, which takes on 

 the aspect of two men groping for each other in the dark, is the delib- 

 erate quieting of the boat so that it will not reveal itself, thus forcing 

 an opponent to utilize active sonar which gives away his location. 



All of these actions suggest a relatively close proximity of submarine 

 to search vehicle. Military strategists may thus consider how much 

 m.ore difficult the problem of detection would be if the entire sea were 

 a military arena and searching were necessary throughout the entire 

 volume of ocean, not simply at the limited depth near the surface in 

 which submarines now operate. They may also choose to consider 



