The gamma records resulting from the passage of airborne radioactive material are sufficiently characteristic so that records from Shots Wahoo and Umbrella can usually be distinguished by inspection, this statement being especially true for downwind locations. The records for Shot Wahoo are unexpectedly complex, showing in one instance at least nine significant peaks in dose rate (Station D 8.0, Figure 3.70). Because of this complexity, the exact time historyof dose rate for a given point near surface zero can probably never be predicted for an underwater shot of this nature. The gamma-time-intensity records for Shot Umbrellaare relatively simple by comovarison. In most instances, the Umbrella records contain a Single high peak in dose rate followed at a later time by a prolonged and relatively low increase in dose rate. The highest recorded dose rate for Wahoo is 42,500 r/hr at 1.63 minutes and at a distance of 4,500 feet downwind of surface zero; that for Umbrella is 200,000 r/hr at 0.32 minute and at 1,760 feet upwind of surface zero, although a maximum dose rate’ has been estimated by Project 2.1 (Reference 86). In spite of generally higher peak dose rates during Umbrella, the cumulative dose for the entire event is usually larger for a given Wahoo station than for a similar Umbrella station. This difference is probably due to the prolonged nature of the total Wahoo event. The cloud of airborne radioactive debris contributing the significant fraction of the total radiation is apparently rather low, since an analysis of the gamma records at a number of fixed locations indicates that the surface winds are the principa] mechanism of transport at distances greater than 7,500 + 1,500 feet downwind of surface zero. High-altitude winds and hodographic plotting are, therefore, not required for the prediction of radiological fields re- sulting from this type of underwater shot. At distances closer than about 7,000 feet, the radio- active material appears to move outward with velocities on the order of 100 ft/sec.—These rates of expansion do not compare well with published fluid-model studies of base surge. 344 4