Blast and Shock Phenomena from Underwater Shots Seven projects investigated free-field blast and shock phenomena on underwater shots Wahoo and Umbrella. Their primary objective was to obtain the free-field input data needed for determination of safe delivery and critical damage ranges for submarines, aircraft, and surface vessels oper- ating in the vicinity of underwater nuclear detonations. In general, there was a rather thorough amount of information available on free-field blast and shock phenomena from HE tests. The only two nuclear underwater tests, Crossroads Baker and Wigwam, however, had left many basic questions unanswered. The biast and shock projects therefore were generally aimed at confirming and expanding Crossroads Baker and Wigwam results, providing a tie-in between data from nuclear and HE tests, providing input data for ships’ damage projects, and generally increasing knowledge of underwater explosion effects. Deep Water Shot, Wahoo. Underwater Pressures - The Naval Ordnance Laboratory and Naval Electronics Laboratory collaborated in measuring underwater pressures. Their main objectives were to confirm Wigwam results on scaling for isovelocity conditions and to study the effects of refraction. Pressure data were obtained at five to nine instrumented stations; peak pressures ranged from 100 to 1800 psi. There were four target ship stations; an adequate number of pressure-time histories (at various depths to 1850 ft) were obtained at the EC-2 (2346 ft) and the DD-593 (8887 ft). Only a few peak pressures were recorded at the DD-474, while at the DD-592 no data were obtained. The data generally confirmed Wigwam results. Thermal gradients showed considerable effect on the pressure field at the 8887-ft range and also influenced peak pressures at depths less than 300 ft at the range of the EC-2,. The pressure-time data will be thoroughly analyzed, primarily by NEL. for refraction effects, using the shot time underwater temperature field provided by ONR-Hydrographic Office personnel. ONR-HO obtained its estimate of shot time underwater temperatures on the basis of bathythermograph (bt) readings from the DD-393 at H-15, H-—5, and H-1 min and pre-shot bt data taken from three points in the array starting on D-7 day. Air Overpressure - The NOL installed three near-surface gages on vessels in the array and seif-recording gages on two balloons at heights of 500 and 1000 ft. Records were obtained from two gages from the balloon station at 3413-ft range and two surface gages at 2346-ft range. Records showed two distinct pulses; it is believed the first pulse resulted from underwater shock transmitted across the water-air interface and the second from bubble effects. Maximum pressure recorded was 0.21 psi at 30-ft elevation, 2346-ft range. Peak pressures showed general agreement with predictions based on HE results. Surface Phenomena - The Scripps Institute of Oceanography measured water waves and NOL studied all other surface phenomena, i.e., spray domes, piumes, base surge, etc. Photography from four aircraft and several surface Stations was the principal means of data collection. With the clear weather. photographic coverage was excellent. Film analysis in progress at this writing is expected to provide thorough documentation of the phenomena of interest. Surface phenomena bore a marked resemblance to Wigwam. Water waves containing approximately 4% of the weapon energy were observed. Hydrodynamic Yield - The Armour Research Foundation failed in its attempt to measure the close-in propagation of the shock front. 25 The technique