to fall on two separate curves, the possible emstence of which may again indicate differences in radial transport velocities or may be due to the discrepancy between the official Task Force surface wind (15 knots from 090° T) and that indicated by surge photography (14 knots from 070° T). For Umbrella, the hypothetical surge radii tend to fall on a definite curve, although again two separate branches at later times could be drawn because of the postulated effects of the atoll reef and because of slight differences between the reported and photographically observed surface winds (Task Force weather report: 050° T, 20 knots; surge photography: 053°T, 16 knets). The radii determined at photo-TOC are fairly constant. Furthermore, they are Similar both to the radii determined at TOP for the later transits and to thoSe determined from base surge phevocrapty (Section 3.3.2}. Although omiy a few points of comparison exist, there are certain general similarities between Wahoo and Wigwam and between Umbrella end Shct Baker Operation Crossroads) despite the large differences in yield in both instances. The Wigwam base surge, like Wahoo, first appears at about 13 seconds and expands at similar velocities; the visible surge velocities for Wigwam have been caiculated from photographs (Reference 14) and are presented for comparison in Appendix E. Each shot generated secondary and perhaps tertiary plumes, which possibly resulted in secondary or tertiary base surges. Fallout or deposited material from the base Surge Seems to have been light at the greater distances. GITR’s installed aboard the YAG-39, which was steaming at approximately 10 knots about 28,000 feet downwind of Wigwam, recorded peak dose rate of 550 r/hr at 16 minutes and a second peak of 640 r/hr at 19.7 minutes (Reference 9). The GITR at Station DR 24.0 on Wahoo recorded a peak dose rate of 589 r//hr at 12.7 minutes followed by a gradual decrease in dose rate, which continued to approximately 25 minutes. Although the shape of the dose rate peaks differ, possibly because one detector was moving while the other was stationary, both the peak dose rates and the time of arrival are comparable (surface wind for Wigwam was 18 knots from 031° T). Furthermore, film packs on the weather decks of the YAG-39 registered cumulative doses ranging from 26 to 35 r, values which compare favorably with the tripod film pack dose of 33 r registered at DR 24.0. Thus, despite the fact that the yields of the two detonations differ by a factor of 3, essentially the same doses and dose rates were observed at similar locations. Umbrella and Baker were quite dissimilar events; however, in the few instances where comparison can be made, nearly the same dose rates during base surge transit were observed on both shots. The column for both shots was probably hollow. During Baker, the fireball was briefly visible at the top of the column. Later a cumuliform cloud similar to those from surface shots was formed, and the column was seen to be open to the atmosphere. During Umbrella, no cumuliform cloud was formed, and the column was probably never open to the atmosphere. The Baker column could have collapsed in a manner approximated by the fluid models just discussed; however, as the Umbrella column collapsed, two high energy jets of water, one vertically up- ward and the second downward, have been postulated at the collapsing apex. During Baker, a heavy rain was observed to fall from the cumuliform cloud at about 3 minutes (References 35, 90, and 99) whereas for Umbrella a similar heavy rainfall from the base surge may have occurred continuously during the first minute after zerotime. If the hypothesis (Reference 90) concerning the formation of this rain is accepted (Section 3.3.1), the early occur- rence of rain would indicate that the individual droplets comprising the Umbrella base surge at formation were much larger than those postulated for Baker. The initial base surge velocities of the two shots are comparable; however, at later times the velocity for Umbrella falls con- siderably below that for Baker (Appendix E). Comparison of dose rate tnformation for the two shots is difficult, since so little rate information is available for Baker. Instruments similar to the std-GITR installed aboard LCT-874 and LCT-332 appear to have recorded an initial dose when the explosion bubble first reached the water surface. The instruments saturated; therefore, the peak dose rate cannot be deter- mined (Reference 5). The record of the LCT-874 (7,500 feet, bearing 045° T from surface zero) is probably most similar to that obtained at DRR 6.7 on Umbrella; the peak dose rates were 4,000 r;/hr at 1.7? minutes for the LCT-874 record and 6,000 r/hr at 2.0 minutes for DRR 6.7. 243