the tropopause were discounted as a barrier, no reliable indications of the significance of the height of the above-tropopause cloud existed. more, even if these factors had been known, Further- the only available long-range fallout data on land-surface bursts were limited to a single low-yield shot (SUGAR of the 1951 JANGLE series), which meant that the assignment of reasonable values to isodose lines derived from the prediction system was both difficult and possibly inaccurate. Consequently, although the elliptical approximations system of fallout forecasting was used on BRAVO to augment other data, it was limited to discussions of the relative merits of the assumptions and scaling upon which it was based. Since there was no real basis for assuming the system was valid, it did not override the many other factors involved in shot decisions. Nevertheless, as the tests progressed and observed fallout effects answered some of the many questions involved, the system was relied upon to a much greater extent (Reference 16, pp. 57 and 58). The elliptical approximations method, or any other extension of the Surface radex area beyond about 6 to 12 hours, was also limited by being based on the ground-zero winds. A new method was needed to accommodate the changes in wind systems as particles drifted farther from ground zero. Thus, during CASTLE a new technique was developed that utilized airborne Particle trajectory analyses and progressive forecasts of wind patterns in accordance with time and displacement aspects of the cloud. Practical methods were devised to apply such a system to the last three CASTLE shots for a valid forecast period of H-hour to H+24 (Reference 16, Tab D). Weather Because fallout forecasts depend primarily on forecasts of wind fields, the accuracy of the CASTLE fallout predictions was related to the accuracy of weather predictions. CJTF 7 in Operation Plan 3-53 (Reference 9) as-~ signed responsibility to CTG 7.4 to administer and logistically support weather elements to provide meteorological data and to perform radsafe Missions required to conduct CASTLE operations. TG 7.4 was responsible for a four-island ground weather reporting element, an aircraft weather 112