water, radioactive materials began to accumulate on the hulls below the water line and in the saltwater systems within the ships. As a result, radiation intensities below deck began to increase, adding to the crew's exposure. When compared to the topside radiation environments resulting from Shot BRAVO and Shot ROMEOfallout, this radiation was "considered more of an operational nuisance than a hazard" (Reference 12). The same phenomenon was observed on the ships at Operation CROSSROADS conducted at Bikini Atoll in 1946. A model was developed in Reference 6 to determine personnel exposure aboard the ships at CROSSROADS due to ship contamination. Because only limited lagoon water contamination data have been found for Operation CASTLE, this model cannot be applied directly to the ships participating at this operation; however, several simplifying assumptions concerning the degree of contamination can be made, which allows portions of the model to be used. Two basic assumptions are made in developing the ship contamination model. The first is that the mixture of fission products present in the accumulated radioactive material on the hull and in the piping of a ship decayed radiologically as phe, This decay rate was verified experimentally for fission products deposited in seawater and on the decks of target ships at CROSSROADS. The second assumption involves the rate of contamination buildup on the hull and interior piping. The radioactive buildup on a previously uncontaminated ship is assumed to be initially proportional to the radiation intensity of the water surrounding the ship, but, as buiidup progresses, a limiting or saturation value of contamination is approached asymptotically. The occurrence of such a saturation effect is indicated by hull intensity readings taken on various ships after their departure from the lagoon following CROSSROADS operations. Based on these assumptions, the exterior gamma intensity of the hull I, (t) of a contaminated ship at time t is given by: I(t) = sth? [exp {- Ep, (o4] , 28 (1)