free air pressure .e. Neither shot showed any ecvide. of a precursor; in the case of Koa, this was contrary to predictions. Cactus overpressures show an unusually slow and as yet unexplained decay for the first 25 to 40 msec. Free-field Ground Accelerations and Relative Displacements. Instru- mentation to measure accelerations at various depths to 100 ft and relative displacement between the ground surface and the 50 and 100-ft depths was installed on both shots at ranges corresponding to predicted pressures of 600, 200, and 100 psi. Ground accelerations up to 1120 g on Koa and 616 g on Cactus were recorded. Acceleration wave forms were more complex than those obtained at NTS; wave forms were influenced considerably by energy transmitted through the earth from ranges closer to the burst. Horizontal accelerations were higher than expected. Peak vertical accelerations showed a more rapid decay with depth than at NTS at similar pressure levels. Relative displacements were smaller than those observed at NTS, largest being less than 5 in. Craters. Cactus crater dimensions of 180 ft radius and 36 ft depth agreed well with predictions. Koa crater dimensions of 1825 ft radius and 160 ft depth were significantly larger than predictions; it is believed the large water tank surrounding the Koa device may have increased the energy coupling with the ground. Simulated Structures. Twenty steel drums with aluminum drumheads were buried at depths down to 20 ft at the 200-psi level on both Koa and Cactus. Results from the few drums recovered at this writing and from lim- ited electronic data available indicate soil pressure decreased with depth to 10 ft and then rose to surface level values at 20-ft depths. As at NTS, the more flexible drums sensed the least pressure. Shock Spectra. Gages consisting of cantilever springs (called "reed gages") were buried at expected ground surface pressure levels of 75 to 200 psi. Each gage recorded the response (displacement) of reeds having resonant frequencies of 3 to 300 cps. Results indicate that soil characteristics have a significant effect on shock spectra. Cactus results appeared to be similar to those obtained during Operation Plumbbob, but response of gages on Koa was generally lower than expected. Air Shock at High Altitudes Theory indicates that the effect of increasing the burst altitude reduces the energy appearing as air blast. On shot Yucca, the objective was to deter~ mine the characteristics of a blast wave at altitudes of about 90,000 ft in order to provide an accurate basis for scaling to higher and lower altitudes. Five canisters containing gages were to be suspended by a nylon line at ranges of 750 to 3000 ft from the device. Blackout of telemetering due to ionization was expected at zero time, but data were to be recorded and transmitted continuously for several minutes after the burst. Canister functions, including turning on the recorders, were to be controlled by a command transmitter aboard the USS Boxer. This project did not attain its objective because of failure of the transmitter about 2 min before shot time. One pressure record from the 3000-ft canister was obtained from the direct transmission but appeared to be spurious. 24 AFWL/HO KS