conditions require southerly components in the winds between the top cf the trades and the bottom of the high easterlies, the shear angle at these two major shear levels varies from about 45° to 180°, In an effort to reconcile critical requirements with available equipment to do the work, a plan was devised as indicated in Tab E. ‘This plan was followed on each shot with some modificetions as indicated below: (a) In an effort %o improve the capability of assessing the effect of the depth of the trade winds on the amount tmd horizontal spread of contamination from this portion of tne elowd stem, and to improve the capabi- lity of early fall-out warning for the EVIMETOK atoll inhabitants during shots at EIKINI, an additional aircraft was utilised in the racetrack holding patter downewind (tradewindewise) from ground sero. This aircraft was flown approx. mately mid-way between the ground andi the racetrack aircraft at 10,000 feet. The exact altitude was left to the diseretion of the aircraft pdlot in order to clear all natural clouds. The results of this effort indicate that for high yield barge shots at BIKINI, trade winds up to 20,000 feet have little effect on ENIWETOK, 180 NM distant. Information to this effect was normlly available by about H plus 3 to H plus § hours for each shot. (b) On some shots the racetract aircraft were also used to obtain aerial readings between the task force fleet ani BIXINT atoll and to survey damage and intensitics on the BIXINE airstrip. - (¢) The lowelevel racetrack aircraft was instructed to remaic in ite holding pattern until released by the Redsafe Officer. Normally, however, this aircraft was given another mission as dictated by the circum stances of the particular shot. The additional mission, as a mule, was to search a sector covering the northern Marshalls and to make low level passes 38