SECRET Chapter | INTRODUCTION The purpose of this experiment was the determination of the dimensions and altitude of each nuclear cloud as functions of time. Primary interest lies in the early stage during which the cloud rises to maximum altitude. Secondaryinterest lies in the intermediate interval during which the cloud extends to ita maximum diameter at the stabilized alti- _ tude. The late stages during which the cloud begins to disperse ard to drift with the several wind layers are important, receive attention but to a lesser extent than the first two mentioned above. : The results are vital to strategists, who need assurance whether a delivering air- _ Craft can or cannot safely avoid the uprushing maelstrom. They are also important to the groups concerned with cloud-sampling operations, and are of potential utility in devising methods of estimating energy release. They areof more than academic interest to practicing and theoretical meteorologists. The photographic method of recording these phenomena was chosen in view of its. ability to record permanently, and for ready analysis, every visible detail of the cloud at any desired time. The anticipated large dimensions of the Castle clouds dictated the placement of the cameras at considerable distances. The use of aircraft as camera platforms was decided in view of the paucity of suitable atolls, and of-the probability of SECRET. bees © sp fe tong natural cloud cover. Several such aircraft were needed, for the purposes of triangulating on the cloud to determine its position, and to provide insurance against failure of any one station to procure satisfactory data. ktaR FORMERLY RESTRICTED DATA