Chapter 1 INTRODUCTION Development of antisubmarine nuclear weapons by the Armed Forces has generated a need for more precise information on radiation fields resulting from underwater nuclear detonations. Prior to Operation Hardtack, several logical field configurations could be postulated, a fact that resulted in a wide variation of predicted conditions. These fields were defined by a com- bination of direct radiation originating in the device itself and of indirect radiation princtpally determined by local meteorology and the dynamics of the radioactive cloud or clouds formed. (Words frequently used in a special sense are defined in Appendix F.) Although the cloud contribution could be modified at specific locations by upwelling of contaminated water, etc., its manifold effect on the total radiation field was considered controlling and was divided into radiation from (1) the cloud and column, (2) the base surge, and (3) fallout resulting from either. Published speculations on the relative importance of base surge (References 1 and 2) as acontributing element showed extremely wide latitude in interpreting existing data. ‘ The desirable standoff distance for a surface vessei delivering a nuclear weapon to its In- tended underwater target 1s determined, however, not only by the radiation field but also by the magnitude of underwater shock. Current estimates (References 2 and 3), based on the assumption that the radiation field was the controlling factor, specified safe delivery distances so large as to place severe performance requirements on existing sonar equipment. Difficulties in interpretation were further emphasized by an operations analysis (Reference 4) of the pruposed underwater detonations made before Operation Hardtack which, on the basis of the predicteg radiation field, indicated a minimum safe delivery distance, from Shot Wahoo detonated at 500 feet in deep water) but which, onthe basis of maximum permissible underwater shock, indicated a minimum Safe delivery distance for Shot Umbrella detonated at 175 feet on the bottom). This operations analysis suffered from uncertainty in the no-wind and downwind base surge dimensions, from geometric simplification of cloud shapes required for mathematical treatment, and from the assumption that an average photon energy truly represented the composite radiant energy. Better definition of the military implications of radiation fields relative to underwater shock obviously required more empirical data. Therefore, the project’s objectives were designed to supply information needed for a precise description of the radiological environment resulting from the two underwater detonations scheduled for Operation Hardtack. 1.1 OBJECTIVES The general objectives were: (1) to measure the complex gamma field at a number of positions within 10,000 yards of each of the two underwater nuclear detonations (Wahoo and Umbrella), (2) to collect limited samples of airborne debris resulting from these detonations, and (3) to expose a numberof test panels to this same debris. SN 23