Operation Wigwam involved a single test of the Mark 90 "Betty" nuclear bomb. It was conducted between Operation Teapot and Project 56 on May 14, 1955, about 500 miles (800 km) 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. Wigwam was the first atomic test in the deep ocean, and it remains the only test that has been conducted in water deeper than 1,000 ft (300 m).
Detonation layout and test
The test device was suspended to a depth of 2,000 feet (610 m) by cable attached to a barge. A six-mile (ten-kilometer) tow line connected the 205-foot (62 m) Cherokee-class fleet tug, USS Tawasa, to the shot barge. Suspended from the tow lines of other tugs were three miniature unmanned target submarines designated "SQUAWS", each packed with cameras and telemetry instruments. Those targets were 132 ft 2.625 in (40.3 m) long, 4/5 scale of the SS-563 prototype hull (USS Tang (SS-563)) to assess effects of the explosion on a submarine hull.
The time of detonation was 13:00 local Pacific Time (noon Pacific Standard Time).
The equipment intended for direct measurement of the explosion-generated underwater bubble was not operational at the time of the shot, but based on other measurements, the bubble's maximum radius was calculated as 376 feet (115 m), and its pulsation period approximately 2.83 seconds.
Underwater sound
The underwater sound from the Wigwam explosion was recorded on bottom-mounted hydrophones at Point Sur and Point Arena off California, and at Kāneʻohe Bay off Oahu, Hawaii. The sound emanating from the explosive test began as an intense water shock wave. As the sound traveled away from the test point, it reflected from topographic features, such as islands and seamounts, located throughout both the North and South Pacific Basins. The reflected sound was then recorded as hours-long sound sequences with varying intensity at Kaneohe and Point Sur. Some of the acoustic energy travelled round trip distances of over 12,000 miles (20,000 km). The sound signals provided one of the early measurements of underwater sound attenuation at low frequencies.
Detonations
The detonations in the United States' Wigwam series are listed below: