18 



Oceanography 1951 



surf and current conditions within the 

 breaker zone. Casualties to landing craft 

 increase rapidly as the breaker height in- 

 creases beyond a relatively ^ow value. Also, 

 with swift longshore currents, landing boats 

 tend to broach on the beach and are un- 

 able to retract after landing. 



The unloading of cargo into lighters of 

 various types is also impeded by high 

 waves. This was graphically shown in the 

 Normandy operation, where the rate of 

 cargo transfer from the ships offshore to 

 the beach was decreased by more than 

 50 percent during periods of high waves. 

 Thus accurate prediction of breaker height, 

 direction of approach, and other surf char- 

 acteristics is valuable in guiding landing 

 operations and may be useful in other ways. 

 For example, it is sometimes possible to 

 gain the advantage of surprise by utilizing 

 marginal conditions in which landings can 

 actually be made, but where the defending 

 forces have a sense of false security because 

 they believe conditions impossible for land- 

 ings. A method for predicting surf condi- 

 tions was developed during the war and 

 taught to meteorologists who were later 

 assigned to various operating staffs. These 

 meteorologists were able not only to pre- 

 dict surf conditions from weather data, but 

 also to select areas along the beaches in 

 which surf heights would be minimal from 

 knowledge of bottom topography and the 

 principles of wave refraction. In the inva- 

 sion of Sicily the defending commander 

 believed that a landing was impossible 

 because of a storm during the night. The 

 aerologist on the American naval com- 

 mander's staff, however, predicted that 

 the waves would drop at dawn and that a 

 landing could be made. 



By far the largest number of oceanogra- 

 phers were engaged during the war in re- 

 search and development for undersea war- 

 fare. The principal problem was, and re- 

 mains, that of detection of submerged sub- 

 marines without being themselves detected. 

 The raison d'etre for submarines is, of 

 course, the relatively poor penetration of 



light and electromagnetic radiation through 

 the ocean. On the other hand, sound is 

 transmitted better through the ocean than 

 through the air. Undersea warfare is thus 

 a deadly game of blind man's buff in which 

 the winning side is most likely to be that 

 with the most acute hearing. Although 

 underwater sound is the chief means of 

 communication with submerged subma- 

 rines, its effectiveness varies widely with 

 varying conditions in the ocean. Vertical 

 temperature gradients in the upper layers 

 refract the sound so that it is transmitted 

 for only a few hundred yards in some 

 cases, or for many thousands of yards in 

 others. Inhomogeneities in the water scat- 

 ter and distort sound. In deep water, 

 these "scatterers" are probably very largely 

 plankton organisms and their predators, 

 concentrated at intermediate depths of 

 about 200 meters. In shallow water the 

 bottom acts as a reflecting surface which 

 at times aids in sound transmission but at 

 other times causes reverberations that pre- 

 vent transmission of a recognizable signal. 

 The ultimate range to which sound can be 

 transmitted depends on the background 

 noise in the sea. In addition to noises 

 made by the ships themselves, there are 

 noises due to breaking waves at the sur- 

 face, to the collapse of bubbles, and, in 

 shallow water areas, to noisy organisms. 

 Underwater sound is absorbed in sea water 

 much more rapidly than in pure water. 

 This has been shown to be due to the 

 presence of magnesium sulfate in the v/ater. 

 Thus every aspect of oceanography— physi- 

 cal, chemical, biological and geological— 

 has direct application to military problems 

 of underwater sound. 



Such are the problems that have brought 

 about generous support of the oceano- 

 graphic laboratories by several government 

 agencies. No doubt many other practical 

 applications will develop. Although some 

 of these are of considerable scientific inter- 

 est, under the present system of govern- 

 ment subsidy in oceanography some import- 

 ant scientific problems tend to be neglected. 



