ABSTRACT The principal objectives were: (1) the determination of total gamma-radiation dose and dosera.e histories aboard three moored ships (destroyers) exposed to radiological environments at locations of possible operational interest about the surface zeros of two underwater nuclear detonations, Shots Wahoo and Umbrella; (2) estimation of remote-source gamma-radiation dose and dose-rate histories at exposed weather-deck locations aboard ship; (3) estimation of total gamma-radiation dose and dose-rate histories in the water adjacent to the ships; and (4) measurement of gamma-ionization decay of a fallout sample collected on one ship a few minutes after each shot. The ships, which were equipped with operating washdown systems, were inStrumented with film badges and gamma-intensity-time recorders (GITR’s). The film badges and unshielded GITR’s supplied radiation data at locations representing major battle stations; GITR’s sub- merged inthe water supplied some data on underwater radiation; and a fallout collector cannected to a fully Shielded GITR supplied gamma-ionization decay data. Radiation histories were obtained on only one Ship for Shot Wahoo. Although histories were obtained on all three Ships for Shot Umbrella, some data was lost because of shock damage. At least 95 percent of the total dose observed on the washed weather decks was attributed to radiation from airborne radioactivity. After Shot Umbrella, weather-deck dose accumula- tion (to 75 percent of final values) ranged between 600 r received within H+26 seconds at 1,900 feet from surface zero and 50 r received within H+150 seconds at 7,900 feet from surface zero. After Shot Wahoo, the doSe accumulation was slower, but the final deck doses were about 300 r higher, despite the fact that the ships were from 1,000 to 2,000 feet farther away from surface zero than was the case for Shot Umbrella. For nuclear-weapon-delivery situations simulated by the two closer-in ships, temporary immobilization could result in lethal or near-lethal doses. After Shot Wahoo, the majority of compartments received doses in excess of 500 r aboard the closest ship and in excess of 200 r aboard the next-to-closest ship. the two ships received doSes in excess of 200 r in many compartments. After Shot Umbrella, Ratios of dose or dose rate in compartments to dose or dose rate on washed weather decks were dependent upon changes in radiation-source geometries and upon the presence of contaminants within the ships. The long-term dose ratios ranged between 0.1 and 0.7 for nonmachinery spaces, and between 0.02 and 0.2 for machinery spaces. Although radiation from the water may have influenced the compartment/deck dose-rate ratios to a considerable degree at later times, the contribution of contaminated water to the total dose observed aboard the ships was probably of little significance. After Shot Umbrelia, gamma-~ionization decay was measured for the periods between H+0.1 and 11.5 hours and between H+23.0 and 34.9 hours. Shot Wahoo. No decay measurements were obtained for