SEARCH FOR THE THRESHER — SPIESS AND MAXWELL 383 



of the sound source. By the time the Trieste made her second series 

 of dives, a more elaborate tracking system, assembled by the Applied 

 Physical Laboratory of the University of Washington, had been in- 

 stalled on the research ship Gillis. In this system a short pulse signal 

 is transmitted from the ship and answered automatically by the sound 

 source (transponder) on the tow. Three receivers are mounted on 

 the ship, and their outputs are fed to a computer which produces all 

 three coordinates of the transponder relative to the ship for each pulse. 



This system was used to track Tneste in her second series of dives 

 and to navigate GiUis relative to a transponder fixed to the sea floor. 

 Throughout the entire operation consideration had been given to the 

 use of acoustic transponders or beacons to mark various reference 

 points, but erratic performance and fear of overloading the area 

 with confusing noisemakers made the Advisory Group reluctant to 

 use them extensively. 



While acoustic methods seemed appropriate for use with most in- 

 strument packages, there was also a realization on the part of some 

 participants that even simple, after-the-fact, knowledge of the posi- 

 tion of photographic equipment relative to the sea floor would be 

 useful. This led to the use of "fortune cookies" — plastic sheets (40 

 by 55 cm.) numbered sequentially, rolled, tied with a soluble band, 

 weighted, and dropped into the sea by one of the ships. This provided 

 strings of spots on the sea floor which were then used for correlating 

 different photographic sequences traversing the same area. This sys- 

 tem also proved useful in orienting observers during bathyscaphe 

 dives. 



Following the second series of Trieste dives the weather began to 

 worsen, and the decision was made to terminate the entire operation, 

 at least for 1963. By that time the debris area had been well de- 

 termined and convincing photographs and pieces of material from 

 within the submarine had been obtained; there no longer remained 

 any doubt that the site of the accident had been found and that any 

 properly equipped ship could return to the debris area at will. The 

 evidence clearly indicated that some catastrophic event had occurred 

 as the eventual result of loss of buoyancy and control by Thresher. 

 It did not appear that any direct information on the chain of events 

 leading to the violent hull failure could be reconstructed from the de- 

 bris thus far found. Some questions still remain, however, which 

 make the area an interesting one for testing new and improved systems 

 for sea-floor search. Specifically, the location and condition of the 

 remains of the pressure hull and the reactor are of considerable in- 

 terest, particularly in view of the variety of credible hypotheses as 

 to their behavior that have been proposed. These range from a 

 hypothesis of complete burial in the sediment, due to high sinking 

 speed, to one of possible temporary surfacing of a portion, resulting 



