ey techies dei. hee Control Group personnel were provided the Scripps Institute vecsel, Horizon, in a technical advisory capacity. Over-all radiclogical-safety supervision was a command responsibility of CTG 132.3. The Horizon was to take station approximately 72 miles north of ground zero at H hour. This position was of concern since wind predictions indicated possibilities of fall-out at this pos‘tion. As a consequence the following equipment was placed aboard: one MX-5, one AN/ PDR-T1B, one AN/PDR-18, one portable air sampler, cight seta of protective clothing, eight sets of self-reading dosimeters, and enough film hadges to supply the crew. §.4.1 Horizon Results At 1240M Nov. 1, 1952, during medium precipitation, radioactive fall-out was detected. The level was low, about 1 mr/hrat the time of detection. The ship was iminediately closed up, and the ventilating syatem was stopped. The spray system was placed in operation, and the ship started circling its position. Within approximately 20 min the level of contamination had increased te an average gamma reading of 5 mr/hr and a maximum beta-gamma reading of 15 mr/hr A message was dispatched at 011327M to CTG 132.3 as follows: “Air Dry 5x, Bullseye 18x, circling on Station.” At 011400M the ship changed course to 180° true, speed 11.5 knots, as directed by CTG 132.3. The contamination levei gradually increased to an average gamma reading of 8 mr/hr and a maximum gamma reading of 35 mr/hr. The spray system was left on at full force as the ship continued on its course of 180° at full speed. At 011520M a message was dispatched to CTG 182.3 as ioliows: “Air Dry 8x, Bullseye 35x, condition stabilizing. Course 180° T, speed 11.5 knots. Will report when clear of fall-out area.” At 011630M the ship stopped; its position was latitude 12°41’ north, longitude 163°05’ east. Two air samples which indicated no detectable activity in the air were taken. Inasmuch as precipitation had ceased, this was a reliable indication tnat the ship was clear of the fall-out area. A survey was made of the ship’s deck which indicated a slight drop in the level of contamination. The following message was dispatched to CTG 132.3 at 011720M: “Air Dry 6x, Bullseye 30x. Air samples indicate we are clear of fall-out area, Lying to. Position Lat 12°41’ N, Long 163°05’ e at >. E.” The ventilation system was placed in operation, and the ship was unbuttoned at approximately 011700M. With the exception of work parties, all personnel were ordered to stay inside the ship. The ship was washed down with a high-pressure hose which lowered the contamination level considerably. The washdown was coropieted by 011930, and the following message was dispatched to CTG 132.3 at O12015M: “Air Dry 3x, Bullseye 20x, washdown completed. Proceeding to Seamount 72.” A message summarizing the above contamination levels was also dispatched to CTG 132.1 at 012045M. A constant vigilance was maintained throughout the night following M day and during M+ 1 day. No further fall-out was encountered. A survey of the ship was made at 020700M which showed the average gamma reading to be 1 mr/hr and the maximum gamma reading to be about 10 to 12 mr/hr. Decontamination was attempted by highpressure s8a!t water washdowns and by tossing overboard those items that were highly contaminated, auch as small pleces of rope and canvas that were of small value. All personnel involved in decontamination operations were carefully checked and decontaminated when necessary. Very little contamination was brought inside the ship. The estimated maximum integrated gamma dosage receivad by any individual aboard (he Horizon was 50 mr. 28 reteseat Bs 5.4 HORIZON ACTIVITIES