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Figure 24. CROSSROADS, Test ABLE cloud.

to 125° from surface zero. At 1000 it was changed to 350° clockwise to 180°. The Red Arc was set to 16 nmi (30 km) downwind from surface zero, and the Blue Arc 22 nmi (41 km) downwind from surface zero. Radsafe monitors were placed aboard all aircraft airborne in the vicinity of Bikini at shot time except in the single-seat F6Fs. The F6F pilots had Geiger counters whose clicking signals were fed into their earphones to warn of increasing radioactivity (Reference C.9.206, Part VII, p. C10).

Two radiological reconnaissance PBMs began making passes over the target area at 0952, starting at an altitude of 2,000 feet (610 meters) and working down to 500 feet (152 meters). They continued until 1427 and then returned to Ebeye Island, Kwajalein. The two radiological reconnaissance B-29s began tracking and photographing the cloud at 1000 and were relieved during the day by two other B-29s. Four TBM aircraft were launched from USS Saidor (CVE-117) between 0910 and 0918. Two developed engine trouble and returned: the remaining two took stations upwind from the drone boats and transmitted boat locations to Begor, which was controlling the drone boats. They completed their mission and departed the area for Saidor at 1238.

Army and Navy aircraft involved with photography and cloud sampling accomplished their missions before 1000. B-17 sampler drones penetrated the cloud at altitudes of 13,000, 18,000, 24,000, and 30,000 feet (3.96, 5.49, 7.32, and 9.14 km) about 20 minutes after the detonation, obtained their samples, and were guided back to Enewetak Island. Three remaining Navy F6F drones sampled the radioactive cloud between 0906 and 0920 at altitudes of 10,000, 15,000, and 20,000 feet (3.05, 4.57 and 6.10 km). All three drones were guided back to Roi and were landed without incident. C-54 aircraft waiting at Enewetak and Roi transported the cloud samples in airbags and filters to Kwajalein. The samples were analyzed as soon as they were removed from the drones by Los Alamos

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