for rapid surveys and depth of penetration measurements, whereas the water sampling technique provides specimens for more complete gamma spectrum studies and for other physical and radiochemical studies. In relation to the depth of penetration measurementg, it should be especially noted that success in either of the procedures used by this project during Castle Shot 5 is highly dependent upon reliability of estimates of fallout below the ocean surface. It is essential that the rate of descent of fallout into the mixed layer be . sufficiently slow that the material is still accessible for measurement at the time of sur~ vey. It has been concludedtentatively that this requirement was met for Shots 5 and 6 since: (1) observations! of the fallout material from the over-water shots at Operation Table 5.1 Comparison of Shot 5 Gemma Field Intensities at 12 Hours (1) as Calculated from Towed Radiation Meter Data, and (2) from Water Sarple Analysis Data Sampling Position Logbook Time 1* Station Latitude Longitude <6 May 1500 1630 1730 1900 1 Surf Surf 2 12-10 12-05 12-00 11-55.3 166-06 166-08.5 166-13 166-16.6 7 May 0130 0500 1400 1820 1900 2300 Surf 3 4 Surf 5 6 8 May 0400 0800 0900 1000 1100 1200 1350 1500 0200 0400 0600 1300 Surf Surf Surf Surf Surf Surf Surf 7 Surf Surf Surf Surf 9 May 1530 8 ae r/br at 3 ft r/br at 3% 23 68 65 33 49 64 a 2h 11-41 167~04.2 12-19.4 166-57.2 13-12 166-40 —-13-00.3--:167--00.5 12-48 167~20 12-30 167-35 9.5 13 1.5 2.9 15 6.4 0.6 13 1.5 3.2 3.7 49 —-12-03.5 :12+32 12-45 12-45 -12-43.5 12-43 12-58 12-59.6 12-19 12-08 -:12-02.5 12-01 -168-00.5 168-08 168-20. 168-16 168-21 168-25 168-27.5 168-26.6 166~39.5 166-10.5 165-44 165-16 2.9 15 8 18 6.2 4.5 15 8.9 38 n 43 8 0.3 17 5.7 18 3.5 1.5 9.6 47 47 uu ib 7.8 11-52 165~34 42 bh * From Table 3.5, colum 8, values at stations are interpolated. These can be identified in Table 3.5 by reference to Logbook Time. ** From Table 4.6, last column. Castle indicated a very small particle size existed which could be expected to settle very slowly in water; (2) from the depth cast data of Shot 5 it appears that the descent of the radioactive material into the water mass comprising the mixed layer was of such a rate and uniformity as to make calculation of depth of penetration entirely feasible. In conclusion, attention is again directed to the evidence that, following Shot 5, an area of about 5,000 square miles was covered with contamination which would be hazardous to human life had it fallen on land. For the smaller-yield Shot 6, the hazardous area was smaller. By hazardous is meant here contributing 250 r total dose during the first 50 hours. Total yield for Shot 5 was estimated at 12.5 megatons and 1.7 megatons for Shot 6. (Reference Summary Report of the Commander, Castle Report ITR—934. ) 1 Reference to Project 6.4, 2.5a reports on Operation Castle. 78