oe 2330 on D-day (H # 17 hours) with readings topside, forward, of 230 to 270 mr/hr. ‘The radiation intensity aft at the same time was 7 m/hr, The peak intensity on the bridge was 6.4 mr/hr. The following morning at 0607, the washdown was secured and at 0725, the ship opened, LST-611 Operations The LST-611 encountered fallout at 1330 on Deday, as indicated by a 5 mr/hr reading on a greased board. The ship was then closed, the radiation intensity increased 2 mr/hr. Washdown was activated at 1415. Intensity on the platform peaked at 90 mr/hr at 1530. the washed deck was 70 mr/hr. At 1400, The intensity on At 0315 on D £1 the washdown was secured. At 1100 an air sample indicated an activity in the order of 1 x 1078nc/ce, and the ship was again closed, The deck and kingpost gave no indication of fallout so, after 5 hours, the ship was opened again, <a, YAG-39 and YAG—4.0 received moderate amounts of fallout after asia (FLATHEAD) and were required to operate their washdown systems, Examination of records from gamma-time stations indicated sufficient reliable data was obtained to attempt an evaluation of the washdown systems effectiveness aboard both ships. The YAG~39 operated about 25 miles due north of ground zero during the fallout period. Due to light surface winds, the ship held station in a fouremile square by use of a figure-cight maneuver, normal to the surface wind, The surface wind bore from the northeast during the event at speeds varying between 14 and 16 knots, Peak activity occurred 10 hours after shot time, the washdown at this time was 12 mr/hr. 45 mr, The activity under The maximm accumulated dose was This compared with a rate of 128 mr/hr and dose of 430 mr from the COMEL/DOE LENL RO ho Gua L f \ “~ \ unwashed area gives an effectiveness of 91 and 89 percent.