issued at H minus 2h and H rinus 8 hours. Theseecnsistoé of trajottepice fromthe shet site for the period H to M plus 72 hears, and were fop such ten thousand feet, from ten te sinty theusané feet, Revised trajectories for the same period were issued af E plue 6 and H plus 15 hours, fince the trajectories represented movement ef air at specie senstant eltitudes, they were act directly useable fer surface fall-eet forecasting. Instead, the forecasts were used by Radsafe perecenel primarily te sesist in analysis of the long-range fall-out aspects and te alert other units ef the Amed Forcea relative te the probable locations and altitudes of areas of airborne radioactive particles. The trajectories were prepared by censtructing proqnostie charts for the period ef tine inwived and using these charte te arrive at the trajectorice, The aumber cf prognostic charte varied ith the simplicity of the eystene, fower being wed vith systems moving o developing alody, and moe for eyutene developing rapidly. The trajectories were derived mechanically by the superposition af ene prognostiechart over encther ant making « sacoth transition from the flew and speedfield of one chart to the Other, oom 4. ConstantAltitude Bellow Flights, During the planing phase of CASTLE, it was proposed that « project be instituted hereby constant altitude balloons wuldbeused to determine thefeasibility of tracing radicsstive debrisat selected levels. This use of these ballconsas predicated ca the assumption thet the movement of that part of the ratio active cloud debris remaining in the air at a particular level eould be deseribed ty a balloon flow at the same level, the balloon and radicactive debris being similtanecusly carried along. Since these balloons could be