weapons, (2) predicting the fallout patterns resulting from other yields and conditions of detonation, (3) evaluating scaling parameters, (4) evaluating immediate external and internal hazards from fallout from high yield devices, and (5) evaluating the logistics involved in decontamination procedurese In addition to these basic investigations, Operation CASTLE results were expected to provide the basis of a theory for the mechanism of particle formtion in the cloud and to sup- ply data relative to the differences between fallout resulting from land and water surfface detonationse 1.3 BACKGROUND Residual contamination resulting from fallout was initially observed at Operation TRINITY4/; subsequent atomic tests nave resulted in residual contamination which was militarily significant for all types of nuclear detonations except air bursts. Experiments were de- signed to document the fallout from both the Operation JANGLE </ and Operation IVY 3/ surface shotse However, the results from these shots are of limited applicability to the CASTLE tests because the yield of the JANGLE shot was very small and in desert sand rather than coral rock, while the min downwind pattern of fallout from IVY Mike shot went out to sea and was not instrumented. The JANGLE surface shot demonstrated that a low yield weapon could cause a significant degree of contamination and definitely established the need for further work on the contamination problem and associated hazards, especially from higher yield surface detonations. Operation IVY provided the first opportunity to investigate the general fallout problem resulting from the surface land burst of a high yield nuclear device, An unanticipated base surge was observed shortly after the CROSS= ROADS underwater detonation1/. It appears that the base surge distributed some contamination from this shot, although the evidence is not entirely conclusive, Attempts to study base surge effects have since been made at JANGLE and at some high explosive tests. These ex=- periments have not determired whether the base surge is a carrier of radioactivity. Operation CASTLE provided the first opportunity to study base surge characteristics from surface water shot. 16