Specifically, the total gamma dose rate as a function of time was to be determined at 21 floating stations in a manner that would permit resolution into an initial dose occurring during the first minute after detonation, a free-field (Appendix F) dose rate resulting from the composite cloud only, and a residual dose rate due to radioactive material deposited from the cloud in transit. Since heavy deposits of radioactive material on the gammadetector itself—or up- welling of highly contaminated water around the floating platform carrying the detector — could have masked the free-field dose, additional instrumentation was installed at specific locations indicated by a theoretical analysis of the situation. The basic time-based gamma measurements were to be augmented by cloud-movement data obtained from photographs and bytotal dose data obtained from film packs mounted in fixed and free-flcating Stations. The gammafields due to airborne radioactive material only were to be correlated with the gamma fields measured aboard three destroyers (DD’s) and one Liberty ship (EC-2) in the pro- posed target array. The data could then be used in conjunction with current theories of aerial transport in the determination of optimum conditions for antisubmarine warfare (ASW) delivery by a destroyer. Such an operations analysis was, however, specifically not an objective of the project. Samples of airborne debris were to be collected aboard the three destroyers to provide addi- tional information on the nature of both base surge and fallout. This information was needed for interpretation of contamination ingress studies and for developmentof better fallout simulants for underwater detonations. Also, test panels were to be exposed for use in later comparative decontamination studies of actual and simulated contaminants. Measurements obtained from the fallout collections and test panels are reported here only to the extent that they influence the basic gamma field determinations made by the project. 1.2 BACKGROUND Shot Baker of Operation Crossroads and the single shot of Operation Wigwam represent the . only underwater detonations of nuclear devices prior to Operation Hardtack. Although the gamma dose and dose rates had been predicted for shallow underwater detonations by means of current scaling theories (References 11 and 12), high-explosive (HE) data (Reference 13), and photographic evidence (Reference 14), these predictions had to rely heavily on data from underground detonations (References 15, 16, and 17) and could therefore be in error by aS much as two orders of magnitude. Although the paucity of underwater information justified this use of underground data, correspondence between the two types of detonations was not established, and speculations on the mechanism of formation and dispersion of radioactive material suggested substantial differences. Specifically, the formation of fallout particles in underwater bursts by solution of fission products in liquid spheres condensed from the vaporized device casing (Reference 18) was thought to be analogous to airbursts rather than underground bursts. The greater ambient pressure might cause condensation to commence at earlier times; thus, an underwater burst could produce particle sizes slightly larger than those for an airburst (Reference 19), their 24