Vv LD The cloud (iireached gigantic proportions, The initial climb of the cloud was about 1,000 feet a second and, before the first minute, it was past 0,000 feet altitude, Within a few minutes the cloud had pushed through the tropopause and had reached altitudes of 120,000 to 150,000 feet. As the cloud passed through the tropopause it began to flatten out until its width was from 150 to 200 miles, The base of the mshroom extended down from 5,000 to 18,000 feet altitude, The stem of the cloud usually was 10 to 20 miles in diameter and, just after the detonation, extended down to the sea, Later, as the wind began to move the cloudaway, the stem base was from 18,000 to 20,000 feet altitude and poured outmaddyrain from one to two hours, There was - severe turbulence in the stem and lower portions of the mshroom, caused by convective forces set up by the extreme changes in temperatures and the many tons of water and material picked up and carried into the cloud, This turbulence lasted for about two hours, and was combined with extremely high levels of radiation, Therefore, the samplers did not attempt to penetrate such a cloud for at least two hours, ~ When the first sampler pilot made a pass at ‘the cloud, he was directed by a quick route of escape in case radiation proved ‘too hot. Normal sampling missions followed between three and one-half to five hours, The clouds, at the Pacific Proving Grounds, usually drifted to the northeast at a speed of about 30 knots, therefore, all sampling usually had to . be accomplished within six hours after detonatio, before the distance to the cloud got too great for the sampling aircraft to safely conduct 105 AFWUHC SWEH-2-003), eh