382 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1964 



successful. The remaining three dives per series, while useful, pro- 

 vided essentially negative evidence, such as evidence on where Thresher 

 was not. During these dives, personnel of the Trieste were able to 

 plot the limits of debris on the bottom, obtain photographs (pi. 2, 

 fig. 2) of many parts of the hulk (including draft markings from the 

 bow), and recover pieces of the debris. The debris area has been 

 described by the Trieste''s pilot, Lt. Comd. Donald Keach, as "re- 

 sembling an automobile junk yard." Unfortunately, a magnetometer 

 aboard the Trieste did not operate properly and the magnetic anomaly 

 observed by the surface ships could not be positively associated with 

 the debris. Radiation detectors, both total-count and pulse-height 

 analyzers, showed the radioactivity in the area to be normal and to be 

 attributable primarily to the potassium-40 in the sediments. 



Results from the Trieste operations showed the microstructure of 

 the bottom to be sufficiently complicated to make further use of surface 

 echo sounders impractical. As a consequence, considerable effort was 

 expended to improve deep-towed instrument packages. The Navy 

 Research Laboratory combined their television camera miit with a 

 proton precession magnetometer and a side-looking sonar (pis. 3 

 and 4). Although there was interference between the various com- 

 ponents, nonetheless, the advantage and practicability of multiple 

 sensors was amply demonstrated. Even with this increase in capa- 

 bility there remained the problem of accurate navigation with respect 

 to the bottom, which hampered all phases of the search operation. 



NEW TRACKING SYSTEM 



As the difficulties in finding Thresher became more apparent it also 

 became clear that a major requirement would be the ability to keep a 

 record of the tracks of various instrument packages and of Trieste in 

 their traverses across the area. Initial estimates of the positions of 

 deep-towed instruments relative to the towing ships were made from 

 knowledge of the ship's speed, the amount of towing wire used, and 

 the angle of the towing wire at the ship. However, the currents in 

 the area are not constant, either as a function of time or as a function 

 of depth; thus, particularly at the low towing speeds which were 

 necessary, the 3000 meters of wire allowed a considerable position un- 

 certainty. It was known from other work that acoustic methods 

 could be used to determine the position of the tow relative to the 

 tending ship. Thus, the Woods Hole group on Atlantis II put into 

 operation a tracking system in which a sound source on the towed 

 package transmitted a signal picked up by three elements, two mounted 

 (fore and aft) on the ship and the third mounted on an outrigger to 

 provide a 15-meter athwartship separation between the receivers. 

 With this arrangement and with knowledge of the water depth from 

 echo sounding, it was possible to compute the approximate position 



