14 May 1955 - Wigwam

The eruption dispersed over 9 billion cubic metres of radioactive seawater, rising to a height of up to 3,600 metres.

On 14 May 1955, the United States conducted the ‘Operation Wigwam’ nuclear test, the first of its kind to be carried out in deep water at a depth of around 660 metres. With a yield of about 30 kilotons, it was around twice the size of the Hiroshima bomb. The test was conducted in the Pacific Ocean, some 800 kilometres from the coast of California.

A Mark 90 Betty type nuclear bomb was used for the test.

Operation Wigwam was conducted to determine the characteristics and lethal ranges of the resulting underwater shockwave and the effects of radioactivity on naval vessels. Three sub-scale submarine-like pressure hulls equipped with measuring instruments were suspended underwater at varying distances from the device, in addition to unmanned surface vessels. The test site was chosen by the U.S. government based on a study conducted by the Scripps Institution of Oceanography, which described it as a “biological desert”.

My husband said that after the detonation for as far as the eye could see the ocean was covered with dead marine life.Joan McCarthy, widow of Operation Wigwam veteran Tom McCarthy, who died of cancer aged 44

The eruption occurred immediately after detonation, covering an area of two and a half kilometres and dispersing over 9 billion cubic metres of radioactive seawater. The fireball-bubble rose to a height of up to 3,600 metres. The vessels closest to the explosion were severely damaged, as was the USS Tawasa, an observer vessel with scientists on board.

The planner’s major concerns were focused on the scientific and military results of the test. Any concerns for the possible hazards facing thousands of men involved first hand and stationed at the blast site, seemed at the time to be secondary in nature.R.J. Ritter, crewmember on the USS Tawasa observer ship
The USS Tawasa observer ship: the propeller shaft was twisted, and hydraulic lines and pipes were broken.

The radioactive mist produced by the blast covered some of the 30 participating vessels. All 6,800 personnel had been provided with film badges to measure radioactive exposure, but no protective gear. The amount of radiation to which participating servicemen were exposed remains contentious. While government sources described the doses as very low, veterans and their families have expressed concern about health implications, arguing that the dosimetry film badges could not measure ionizing radiation (radioactive particles) and pointing to cases of early cancer deaths among participants.

It was necessary to direct a few ships into radioactive water. Salt-water systems and hulls were contaminated by this experience but not to a level high enough to become a health hazards when the proper precautions were taken. It was also necessary to bring radioactive material, such as water samples, buoys, and cables, on board some ships. Adequate precautions prevented serious health hazards.Operation WIGWAM, Report of Commander

Increased levels of radioactivity were monitored from four days after the test at the California/ Mexico border, at a distance of 800 kilometres. See chapter effects of nuclear testing for background information on radiation hazards from nuclear testing.