TAB A FLATHEAD EVENT OPERATION REDWING 1. The FLATHEAD Shot was fired at O626M, 12 June 1956 on a barge © Jocated approximately one-half mile South of YUROCHI Island (DOG) in the BIKINI Atoll. The cloud reached an estirated 60,000 feet. The lower ’ portion of the cloud and stem moved to the West at approximately 15 knots, 2, The fallout forecast for FLATHEAD was calculated on the basis of 2a water surface burst and a fission yield of / | Orogram “THO fallout murchery on H+l Day indicated the fallout sector as 21,00 through 0504 eftending 100 miles with probable hot line on bearing 010° with an average intensity on the surface of the water of 1 mr/hr. The plus 8-hour summary gave same sector with hot line definitely fixed on bearing of 3109. Frogram TWO surveys confirmed the fallout forecast to be within the acceptable error of forecasting. 3. Cloud penetration aircraft reported the middle and upper portion of the cloud moving to the northeast at H+l Hour. The cloud contimed tc move in a general north-northeasterly directicn throughout H+3 Hours. 4, The aerial monitoring (F2V aircraft) reported the ENYU (NAN) air- strip te be free of debris and radiological hazards. Based on survey information Reentry Hour was established at 9830M, 12 June. The initial helicopter survey at H+3 hours reported fallout still occurring over the reef and lagoon in the vicinity cf YUROCHI (0G). In general, the initial