a. 7 BUTTERNUT EVENT OPERATION HARDTACK 1. BUTTERNUT was ea barge shot situated 4,000 feet west of Yvonne Island in the ligoon at Eniwetok, The device was detonated at 0615M, 12 Mey ee The cloud rose to 35,000 feet, then stabilized at 30,000 feet. Main cloud movement was to the northvest, with most of the fallout deposited in the sea. The only islends receiving substantial contamination were Alice, with 650 mr, and Mack (directly in the cloud’s path), with 30 r. Yvonne, less than a mile from ground zero, read 100 mr. All of the above rerditgs were surface intensities corrected to H+3 hours. 2. Fallout prediction was generally accurate, except that only the northwest quadrant of the atoll received substantial contamination instead of the whcle northern helf, as forecast. Nearly all of the fallout fell between the radials of 260 degrees to 300 degrees from ground zero. Ilsngth of the radials is approximsted at 110 miles; however, no direct observations are available to bear out this estimate. No fallout was detected outsides BEST COPY tTSLABLE the hazard area announced on D-1. ™ ea TAB A fm #7 . hood we eek ’ 43