compartment's total dose rate. Radi al Environment. This study was to document the radiological environment resulting from underwater nuclear detonations. The gross gammag fields from shots Wahoo and Umbrella were defined by means of GITR rumentation located on coracle platforms, as well as on the major target a. These measurements were supplemented by those of total gamma dose made with floating film packs located throughout the target array. Incremental collectiensof radioactive material deposited from the resultant base surge and cloud permitted resolution of the gross gamma fields into initial, free-field, and residual doses and dose rates. Underwater probes were used to obtain information on radiation from radioactive materials suspended in the water. For Wahoo and Umbrella, it was found that nearly all the total gamma dose occurred within 15 min after zero time and was due to the passage of air-borne radioactive material. However, the records of gamma dose rate versus time obtained from the two shots show pronounced and characteristic differences in the transiting gamma fields. Gamma doses in excess of 100 r occurred within the first 15 min at downwind distances of lesa than 16,500 ft for Wahoo and 11,000 ft for Umbrella. On both shots the dosage due to deposited radioactive material on the ships and coracles was from light to insignificant. A study of the downwind gamma data showed that a distance of approximately 23,000 to 28,000 ft from surface zero should be maintained in order to assure a total free-field dose of less than 25 r. High Altitude Shot, Yucca Neutron flux and gamma radiation measurements for the Johnston Island part of the Operation are covered in the summary pertaining to Teak and Orange. Measurements of the =eutron flux spectrum and total prompt gamma ray flux resulting from th: detonation of shot Yucca, a titude of approximately 90,000 ft were planned. burst at an al- All data were to have been recorded and subsequently telemetered to a@ recording ground station. The instrumentation was contained in a canister suspended 2,750 ft below the nuclear device by means of a nylon line. Due to failure of the command transmitter, which controlled the canister operational functions, the instrumentation was inactive at zero time, and no data were obtained. Projects Participating during Developmental Shots Neutron Flux Measurements. This was a program to document the neutron flux and spectrum as a function of distance for two shots in the To achieve this objective, the project participated during shots Yellowwood and Walnut. The measurements were extended during the 28