IV test director samples could not be guaranteed because of vapor clouds expected around the atomic cloud. As the atomic cloud drifted in the wind, vapor clouds became thicker and thicker, The B-50 sampler control aircraft, with Dr, Plank aboard, climbed above the overcast with little success in finding the atomic cloud. Back through the overcast there was approximately one-fifth of the atomic cloud below the vapor clouds, Dr. Plank called for the F-8l, aircraft immediately and began directing them into this lower portion, The overcast continued to thicken and lower so that, after two- and-one-half hours following the detonation, sampling stopped. By that time the atomic cloud was some 300 miles from Indian Springs Air Force Base, Two aircraft took small samples jswhile the last aircraft which attempted to enter the cloud received none,“°? Conclusions Operation UPSHOT/KNOTHOLE sampling missions were not greatly different from the missions flown in former tests. however, were more refined. The sampler functions, Colonel Houghton, Lieutenant Colonel Fackler, and Dr. Plank had concentrated on methods of reducing the radiation dosages received by the sampler pilots so that larger, more valuable cloud samples could be obtained while the pilot personnel remained safely within the limits established by the Atomic Energy Commission, 90 HLLHG SWEH -2-003), ttc Fs