376 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 64 



tial effort, when there was a true need for emergency action. Later 

 on, the feeling of pressure continued because all the major participants 

 had previous plans for research expeditions, to which they were 

 anxious to return. As time passed and the difficulties became more 

 apparent, there was pressure to bring the operation to a successful 

 conclusion before bad weather set in, in the fall. 



The individual tecliniques which were immediately recognized as 

 potentially useful and which were already being employed in some 

 fashion in exploration of the sea floor were use of acoustic echo 

 sounders or near-bottom sonar; magnetic, electric, radiation detection; 

 photographic detection ; real-time optical detection, either direct view- 

 ing or viewing by closed-circuit television from deep-operating craft ; 

 and dragging or dredging. The group rejected the last alternative, 

 primarily on grounds that it would disturb the site in ways which 

 might confuse interpretation of the situation when the wreck was 

 found. Direct observation could not be implemented initially, but 

 the bathyscaphe Trieste was immediately transported by ship from 

 San Diego to Boston and readied for use. 



Of the tecliniques available, the one which was most immediately 

 and widely applicable was use of the precision echo sounder. This 

 device consists of a downward-looking broad-beam sound transmitter 

 and receiver; the received signal is displayed on a facsimile-type 

 recorder having a very stable time base. This display produces, on 

 an expanded scale if desired, an analog record of the echo return times 

 for successive sound pulses transmitted into the water as the ship 

 travels along. In normal use, this system provides an approximate 

 representation of the topography for the construction of charts or the 

 study of shapes of naturally occurring features. For search purposes 

 this teclmique would be useful only if the sea floor were relatively 

 smooth. If this were the case, attention would be directed to search 

 for a small crescent-shaped pattern superposed on the echo returns 

 from the sea floor. Simple geometry shows that the return from a 

 submarine will be the first echo, even if the hulk is 150 meters to the 

 side of the search ship's track, for target height of 10 meters in water 

 depth of 2500 meters (about that in the search area) . Comprehensive 

 application of this teclmique thus dictated a stringent requirement 

 for a navigational capability not normally possessed by research 

 ships in this area. 



SEARCH AREAS AND ACCURACY 



The navigational problem was first met by the use of the Loran C 

 electromagnetic system. After difficult-to-obtain Loran C receivers 

 were obtained, it became rapidly apparent that the shore station 

 locations were such that only one coordinate was useful. Therefore, 

 arrangements were made to utilize, in addition, a Decca system in the 



