yield used for the effects studies on aircraft in flight. An overpressure of 0.81 psi was recorded on the B-36; damage to the B-36 necessitated replacement of the bomb-bay doors, aft lower Plexiglas blisters, and the radar-antenna radome. The specific techniques used during Castle to predict thermal inputs and responses were inadequate for accurate, close positioning of the aircraft. The procedures utilized to predict blast effects at overpressures leas than 1.0 psi were satisfactory. In general, good correlation was obtained between measured and predicted values. Results of contamination-decontamination studies with the two remote-controlled ships (YAG-39 and YAG-40) indicated that washdown effectiveness based upon the reduction of accumulated gamma dose averaged approximately 90 percent. Measured shielding factors on the YAG-40 were between 0.1 and 0.2 between the second and upper deck and varied from 0.03 and 0.05 between the upper deck and the hold. Results of the Strategic Air Command’s evaluation of interim indirect~bomb-damage assessment (IBDA) procedures indicated that current equipment and operating techniques were adequate. Scope photographs showed the typical horesehoe-shaped configuration during the early moments following time zero. The location of ground zero was established within an accuracy of 600 to 1,100 feet by determining the center of curvature for the horseshoe configuration. Computation of yields proved inaccurate. In the studies of the effects on the ionosphere, it was observed at the Parry Island ionosphere recorder that severe absorption occurred for several hours following all megaton shots. It appears that the duration of the disturbances was related in some manner to the yield of the device and was about inversely proportional to the distance. li: the investigation of the problem of long-range detection of nuclear explosions, azimuthal errors within +3 degrees were experienced in locating the source by utilizing the electromagnetic effects. Reception and identification of detonation pulses when the time of detonation was known to a millisecond were relatively easy; however, to do the same thing on a 24-hour basis with the detonation time unknown would have been much more difficult. It was found that more information is needed on techniques of discrimination. There appeared to be an approximate relationship between yield and the frequency at which peak energy occurs. The photography program obtained data that was more complete and accurate than any obtained on previous operations. Good measurements of cloud height and diameter over a 10-minute interval were compiled for the five shots photographed.