weighing from 1400 to 4400 lb was planned to simulate underwater nuclear attack agafitethe DD-592. The tests were carried up to the threshold of shock damage. but stopped after detonation of the third charge to avoid the Hrobability of serious damage to the DD-592 prior to the Hardtack full scale clear tests. The results indicated that the shock wave pressure satisfactorily simulated the initial shock waves from a nuclear detonation. Four unmanned major target ships, three destroyers, and an EC-2 merchant ship were instrumented and exposed to the Wahoo and Umbrella underwater detonations. In addition, three manned fleet operating ships, submarine SSK-3, and destroyers DD-72& and DD-826 had a small amount of instrumentation aboard and were also exposed to Wahoo. The SSK-~-3, unmanned, and a four-fifths scale submarine model, Squaw 29, were also exposed in Umbrella. The shock response of equipment as well as equipment foundations (which included hulls, bulkheads, decks, and superstructures); was recorded by 325 velocity-time meters and self-recording shock-spectrum gages and 40 high speed motion picture cameras. The following tentative conclusions with respect to damage to machinery and equipment may be made. 1, The minimum safe range for delivery of an antisubmarine weapon by destroyers is 3000 ft for Wahoo conditions and 2400 ft for Umbrella conditions. Damage or malfunction of particularly delicate equipment, e.g., some types of electronic equipment, may occur at even larger ranges. 2. The range for moderate damage for delivery of an antisubmarine weapon by destroyers is between 2300 and 3000 ft for Wahoo conditions, and. less than 2400 ft for Umbrella conditions. 3. The minimum safe range for a submarine is 2500 ft for Umbrella conditions. For Wahoo conditions. 10,000 ft is conservatively safe; later analysis will permit determination of the minimum safe range. 4. The safe range and moderate damage range for submarine and surface targets is determined by shock damage to ship's equipment rather than by hull damage for both Umbrella and Wahoo conditions. Gages and recording centers were installed on the three target destroyers and the EC-2 merchant ship in order to document the basic hull response of these surface ships. A total of approximately 170 gages recorded velocities. displacements, deflections. pressure, strains. rolling. and pitching. The hull damage was significant but less than expected on the attacked side of the EC-2 and negligible on the target destroyers. The following tentative conclusions were reached: 1. From the standpoint of hull deflection the following safe delivery ranges for destroyers have been demonstrated: 2900 ft under Wahoo conditions and 1900 ft under Umbrella conditions. No statement can be made at this time, from the viewpoint of hull deflections, concerning the minimum safe delivery ranges except that they must be considerably smaller than the above values. 2. The estimated horizontal letha! ranges for the EC-2 from the standpoint of hull deflections are 1700 f: for Wahoo conditions and 1300 ft for Umbrella conditions. 3. Check points for small scale CERD model experiments were obtained from both Wahoo and Umbrella. For Umbrelia, the submerged four-fifths scale submarine model, Squaw 29, at a range of 1600 ft was instrumented with strain gages; pressure gages; deflection gages; high-speed cameras; and roll. depth, and flooding indicators. The hull was plastically deformed but did not rupture. Four of the ten ex30