blast and thermal effects. For the Eniwetok area, the wind patterns were carefully studied both pre-shot and post-shot for possible adverse fallout effects in that direction. Cloud tracking was the primary post-shot method of assuring safety to the personnel at Eniwetok and while evacuation was not effected at that atoll, the capability existed to execute such an operation should the need arise, B. Off-site Operational Considerations. In addition to concern for the on-site area, the radsafe planners had to take into consideration many factors which are well outside this area. The possibility of contamination of the many na- tive-inhabited atolls surrounding the PPG, for example, necessitates careful planning prior to a test series. In general, the radsafe off-site operations, based primarily on cloud tracking, aerial survey, and ground monitor stations, were carried out as planned and were adequate for the CASTLE tests. As the Operation. progressed certain modifications were made to satisfy unusual circumstances, 1. Native Populations and Evacuation. Previous to the Operation all atolls except Ujelang (and Eniwetok for Bikini shots) were considered to be in a favorable location with respect to fallout. However, there was a general movement of air particle trajectories to the east on all shots re- gardless of the initiai direction of the winds near ground zero, The net consequence of this action was the eventual transport of the most significant portion of the cloud (i.e., approximately 20,000 feet to 60,000 feet) to the east where subsequent subsidence of the 192