Tuesday, April 3, 2012

Underwater Atomic Test: Operation Wigwam

"Operation Wigwam involved a single test of the Mark 90 Betty nuclear bomb. It was conducted between Operation Teapot and Operation Redwing on May 14, 1955, about 500 miles southwest of San Diego, California. 6,800 personnel aboard 30 ships were involved in Wigwam. The purpose of Wigwam was to determine the vulnerability of submarines to deeply-detonated nuclear weapons, and to evaluate the feasibility of using such weapons in a combat situation. The task force commander, Admiral John Sylvester, was embarked on the task force flagship USS Mount McKinley (AGC-7).

The test device was suspended by a 2,000 feet (660 meters) cable under a barge. A six-mile tow line connected a fleet tug, the Tawasa, and the shot barge itself. Suspended from the tow lines of other tugs were three miniature unmanned submarines named "Squaws", each packed with cameras and telemetry instruments.

The time of detonation was 1300 hrs Pacific Time. The test was carried out without incident, and radiation effects were negligible. The device yielded 30 kilotons. Only three personnel received doses of over 0.5 rems...


Operation WIGWAM was a deep underwater nuclear test conducted as part of the 1945-1962 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 6,800 personnel and 30 ships took part in this operation under the Commander, Joint Task Force Seven.

A single, 30-kiloton nuclear device was suspended by cable from a towed unmanned barge to a depth of 2,000 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 submarine-like 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 for, the device was detonated at 1 p.m. Pacific Daylight Time on May 14, 1955.

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."

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