1 September 1981 Fact dna Defense Nuclear Agency eet e HO ADE Public Affairs Office Washington, D.C. 20305 Operation WIGWAM Operation WIGWAM was a deep underwater nuclear test conducted as part of the 19451962 United States series of atmospheric nuclear tests. It took place in May 1955 in the Pacific Ocean approximately 500 miles southwest of San Diego, California, under the joint administration of the Atomic Energy Commission and the Department of Defense (DoD). The purpose of the operation was to determine the radiation and pressure phenomenology associated with nuclear detonations at great depths and to ascertain the effects such explosions would have on submerged and surface vessels. Approximately 6544 personnel and 30 ships took part in this operation under the Commander, Joint Task Force Seven. Test © Array A single, 30-kiloton nuclear device was Suspended by cable from a towed unmanned barge to a depth of 2000 feet in water that was 16,000 feet deep. Located at varying distances along the approximately six-mile (30,000 feet) long towline between this barge and the fleet tug, USS TAWASA (ATF-92), were a variety of presSure-measuring instruments, unmanned and specially prepared submerged submarinelike hulls (called squaws) as well as instrumented and also unmanned surface boats. The ships and personnel conducting the test were positioned five miles upwind from the surface detonation point with the exception of USS GEORGE EASTMAN (YAG-39) and USS GRANVILLE S. HALL (YAG-40). These two extensively reconfigured ships, equipped with special radiological shielding, were stationed five miles downwind of the surface detonation point. With all the ships at their assigned Stations and all personnel accounted Pacific Daylight Time on May 14, 1955, © for, the device was detonated at 1:00 P.M. Radiation Contamination WIGWAM resulted in three sources of radiological contamination: airborne activity, residual fallout and water contamination. During the first three seconds after the detonation, the radioactive debris was primarily contained within an initial bubble formed by the interaction of thermal energy with the water. Then, beginning at approximately H + 10 seconds (ten seconds after the detonation) these gaseous products began to reach the water surface, forming spikes and plumes reaching maximum heights of 900 to 1,450 feet and emerging from an area roughly 3,100 feet in diameter. As the plumes fell back into the water, a large cloud of mist was formed. This was the base surge which at H + 90 seconds, had a radius of 4,600 feet and a maximum height of 1,900 feet. The visible surge persisted to H + 4 minutes. At H + 13 minutes, a foam ring appeared with a 10,400 foot diameter. The area within this ring probably approximated the extent of the contaminated water. While the surface water initially showed significant contamination levels, the water dispersed and radiation decayed rapidly, so that by May 18 the maximum radiation reading found over an 80 square mile area was on the order of one milliroentgen per hour (mR/hr) at 3 feet above the surface. Contami@ nated water was found at several depths during the weeks following the test and tended to be in layers a few feet thick. 4