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A study of operations in the THRESHER area indicated that an angular coverage of about 120 degrees is required for an opti-mum photographic search of the ocean floor. While this coverage has been obtained using a three-camera array, the time and water needed to process and view the film make it desirable to develop a single camera capable of covering the required angle. In order to obtain this sort of coverage with a single lens, it is necessary to replace the usual plane glass window with a hemispherical shell. The design criterion for mating a wide angle lens to a hemisphere were determined and a model 204 EG&G camera was modified to provide a 114-degree angular coverage. This camera was used successfully in search operations off Palomares, Spain. In the weeks that followed the loss of the submarine, THRESHER, it became apparent that though man had made considerable progress in his studies of the deep ocean, he still lacked the ability to search even a relatively small area of the ocean floor. Optic, acoustic, magnetic, and other sensors, which could be used at great depths, were in existence but it was still necessary to learn how to use them as search tools. In the early days of the search, there was a feeling that the short ranges inherent in underwater optical devices made them ineffective tools for ocean floor search. Later came the realization, that while other longer-ranged sensors were useful in locating bottom anomalies, only optical techniques had sufficient resolution to identify theseanomalies. With this realization, came the necessity of making the best use of the optical range available. At the time of the loss of the THRESHER, multiple exposure camera systems, useable at great depths, were available from a number of commercial sources. These systems had been developed to aid marine scientists in their study of the deep ocean. They were generally used either singly or as stereo pairs, a practice which continued throughout most of the first year of the THRESHER search. On the final trip to the THRESHER area in 1963, U.S. Naval Research Laboratory personnel used two cameras, one tilted to each side in order to obtain wider coverage.
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