378 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 64 



of the Thresher sinking, the Navy Research Laboratory had under test 

 a slow-scan underwater television system. It was being developed by 

 the laboratory for direct observation of the bottom in real time, to 

 correlate with acoustic reflection measurements, as well as for examina- 

 tion of instruments and structures emplaced on and in the bottom. 

 The unit had been tested through 6,700 meters of cable on the dock, but 

 had never been to sea or even in the water. By accelerating the de- 

 velopment program, the system was readied for use aboard the Gillis in 

 May. Although the television had an advantage over photography in 

 providing real-time observations (one picture every 2 seconds), it had 

 a relatively poor 600-line resolution. Fortunately, the cameras could 

 be activated to give pictures of better resolution when interesting ob- 

 jects came into view on the tube. Many thousands of "looks" at the 

 bottom were obtained by this teclinique, complementing tlie results 

 obtained by photography. 



DEBRIS IS PHOTOGRAPHED 



In spite of lack of knowledge of the exact location of the photo- 

 graphic or television camera (on the end of 2,500 meters of wire) 

 relative to a lump on the sea bottom that had been found by the echo 

 sounder at the surface, the ships criss-crossed the area with some 

 success. Using combined photographic, echo ranging, electric poten- 

 tial, and radioactive equipment, part of which was loaned to Woods 

 Hole by Schlumberger, the Atlantis II searched in a predominantly 

 north-south pattern based on Thresher^ last known course of 090 

 degrees, in the hope that some evidence of her passage might be de- 

 tected. This strategy paid off with the receipt of the first pictures of 

 fresh man-made materials on the sea floor, and was used by other ships 

 to build up, gradually, sufficient evidence to indicate a streak of debris 

 about 1,000 meters wide and at least 4,000 meters long. However, none 

 of the pieces of debris photographed at this stage showed any item 

 clearly identifiable as belonging miiquely to Thresher. 



At this time the need to identify the debris streak with Thresher 

 became strong enough to override, temporally, the earlier restriction 

 against dredging. Conrad had on board equipment normally used to 

 gather rock samples from the sea floor. She dragged this across the 

 debris area and, in several passes, recovered some envelopes containing 

 spare gaskets. These were identified, from notes on the envelopes, as 

 being definitely from the interior of the Thresher. Similarly, the 

 Atlantis II dredged up pieces of battery plates that were later identi- 

 fied, by chemical analysis, as being of the type carried on nuclear 

 submarines. 



Dredging, photography, and echo sounding were three techniques 

 which could be used in this search without any modification. Mag- 

 netometers [obviously applicable in a search for a 3,000-ton (2,700- 



