aboard ships 3,000 feet or closer to Umbrella saturated during the first major dose rate pean should be noted. Maximum dose rates . 0.35 minute have been esti- mated by Project 2.1 from the records of instruments shieldedbelow decks (Reference 86). The cumulative dose at various times after zero time has been calculated by numerical integration and is presented in Table 3.9. Despite the higher peak dose rates observed during Umbrella, the average total dose for downwind stations closer than 12,000 feet is approximately two to three times higher for Wahoo than for Umbrella because of the longer surge transit times. The fact that many of the close-in Stations on Umbrella overturned has little effect on the rela- tive magnitude of the cumulative dose, since all these coracles received most of their total dose prior to the estimated time of overturn. A rough check of all GITR records demonstrates the observed dose rates to be consistent with a base surge containing fission product activity available. As indicated later, the assumption that the radioactive base surge from an underwater detonation disappears Solely by a process of decay appears justified for estimates of tactical hazards during the first 15 minutes after detonation. To limit weather deck exposures a combatant ship must remain downwind of Wahoo and downwind of Umbrella. Closer upwind and crosswind approaches without exceeding these total weather deck exposures are of course possible, but, due to the unpredictability of close-in phenomena, these closer approaches must be determined by careful operations analysis. Another important tactical consideration in problems involving ship maneuvers immediately upwind of a receding surge is the possible existence of relatively invisible radioactive remnants streaming behind the visible surge. Al] radiological observations, however, indicate that base surge is the controlling tactical problem and that waterborne radioactivity is definitely of secondary importance. The passage of radioactive foam is, however, presumed to cause the spikes (Appendix F) in dose rate of 3,000 to 6,200 r/hr between 5 and 15 minutes observed at some crosswind coracles and would represent a serious hazard to small boats. Any more detailed comparison of the gamma dose rate records with various features of the base surge requires the application of some correction for radioactive decay and the adoption of some formal means of estimating the combined effects of surge irregularities, radial expansion, and local surface winds. Because of the limited data available, no proper Solution to any of these problems exists. The observed gamma dose rates are corrected to 1 minute after zero time by applying the standard decay correction (Ficure 8,5) to dose rates read off the std- GITR record (unless otherwise noted) at intervals of a tenth of a minute. The resuiting curve cailed the normalized dose rate has been superimposed as a dashed line on each gammarecord and is also used in Section 3.3.1. The approximate effect of surge movement and irregularity ata given coracie is estimated from base surge photography as previously described. Two representations of the approximate base surge position—-the boundary plot and the transit plot (Appendix F) to be described later——are presented with each gamma record together witha number of tables summarizing important information and assumptions relevant to that particular record. The application of a single decay curve (Figure B.5) to obtain the normalized rate curve is considered justified, since the principal clouds of airborne radioactive material appear to have been small enough to be seen as a whole by the std~GITR. The resulting normalized rate curve is useful for studying surge dynamics where radioactive decay is simply an additional and irrel- evant complication. It cannot, however, be considered as accurate as the observed gamma dose rate because of possible deviations from the standard decay curve and because of unavoidable mathematical approximations used in its determination. Although the normalized rate curve is sometimes continued after passage of the base surge, its use for other radiating Sources is not justified. The cumulative dose under the normalized rate curves has also been calculated for various times after zero time by numerical integration and ts presented in Table 3.10. Because of complications due te waterborne sources, the calculation of the camulative normalized dose is stopped as soon as the gamma record indicates completion of surge transit. Although the cumulative normalized dose contains a number of inherent inaccuracies, tt may be 124 Pages 125 & 126 Ww deleted.