( used by Armour was | ( rreviously successful Wigwam metn The lack of a stable platform was tne principal cause of failure. Shallow Lagoon Shot, Umbrella. Underwater Pressures - NOL successfully measured underwater pressures at 16 stations. Records obtained at distances of 500 to 8000 ft from surface zero, at depths from 10 ft down to 130 ft, covered the pressure range between 50 and 9000 psi. Peak pressures were in agreement with theoretical predictions and HE results. Peak pres- sures decayed with distance at a significantly higher rate than would occur in free water. The main shock was preceded by a smali gradual increase in pressure which was induced by ground shock. At close-in stations, near- ideal wave forms were observed; at 3000-ft range and beyond, wave forms were complex. A cavitation pulse was observed at all stations at 750-ft range and beyond; maximum cavitation pressure measured was 314 psi at 1884-ft range. Air Overpressures - NOL used a combination of 32 rockets, five balloon stations, and seven surface stations to document the air overpressure-time field at ranges up to 8000 ft from surface zero and altitudes up to 15,000 ft. Nine of 20 rockets recovered yielded usable data; eight additional rocket records may yield usable data after further evaluation. Five of the seven surface stations and one balloon station produced good records. Surface data showed good agreement with predictions based on HE results and indicate the use of 100% efficiency in scaling HE data to the nuclear case is reasonable. Peak pressures from rocket records were low compared with HE predictions. Maximum pressure recorded, 1.88 psi, was at 2500 ft altitude at a range of 2000 ft from surface zero. Surface Phenomena - NOL investigated surface phenomena in general while SIO concentrated on water waves. EG&G provided excellent photograph- ic coverage of surface phenomena from four aircraft and several surface stations. NOL obtained good records of temperature and humidity changes at five stations within the base surge. These records show well-defined tem- perature changes which correlate well with arrival of base surge as visually observed. SIO successfully measured the waterwaves from a number of stations and by a variety of means. The most interesting of these measurements came from three stations about 1700 ft from surface zero. They indicated that the highest wave was the first of the wave train. fronted and had a 22-ft span from crest to trough. It was steep Hydrodynamic Yields - ARF attached two strings of blast switches and one doppler system to a taut cable running outward from the Umbrella de- vice with the aim of measuring the time interval between closures of the blast switches and the rate of phase change of an rf signal fed into the doppler cable. Data were received in the zero LCU and telemetered to a remote location. Records were obtained for the blast switches only as the doppler cable was crimped during installation. ed an effective hydrodynamic yield of about Preliminary data analysis yieldgi@ssure-distance curves from which hydrodynamic yields are dete , however, showed an as-yet unexplained deviation from the slope expected on the basis of Wigwam results. Crater Dimensions - ONR and HO measured the Umbrella crater by means of preshot fathometer survey and a postshot lead~line and fathometer survey. A crater of about 20 ft depth and 1500 ft diameter was found. 26 AFWLHO 25