Operation Upshot-Knothole; 1953 - Nevada Proving Ground

By 1953 a pattern of test activity at the Nevada Proving Ground had emerged. Through the fifties, every year or (every other year if a pacific test series intervened) a series of several shots was fired at the NPG over a period of three or four months to address a wide variety of objectives. Upshot-Knothole was just such a scatter-shot effort. Technical information to assist in weapon design was obtained in several tests. Efforts to prepare the U.S. military for atomic combat continued with proof-tests of a number of new tactical weapons, including the first nuclear artillery shell. The tests provided additional experience and information for planning atomic combat operations. Important information was also obtained for civil defense efforts.

And critically important - Upshot-Knothole also tested the radiation implosion systems for the world's first deployable thermonuclear weapons which would be proof-tested in Operation Castle the following year.

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An estimated 18,000 DOD personnel participated in observer programs, tactical maneuvers, scientific studies, and support activities. Members of all four armed services participated in Exercise Desert Rock V.

This operation exposed exercise personnel to nuclear tests, and thus radiation, more aggressively than previous ones. Observation by troop formations were conducted at what was calculated to be the minimum safe separation distance, with many personnel being exposed to multiple tests. Under current occupational radiation exposure limits (0.3 rem/week and 5 rem/year) this would would limit maximum exposures to 3.3 rems over the 11 week operation. Approximately three thousand soldiers reached or exceeded this limit, with 84 exceeding the annual limit (the highest recorded exposure was 26.6 rem). These exposures do not produce observable symptoms, they simply increase the lifetime risk of cancer a small amount.

The effect on the downwind civilian population, taken together, was much worse. Uphot-Knothole released some 35,000 kilocuries of radioiodine (I-131) into the atmosphere (for comparison, Trinity released about 3200 kilocuries of radioiodine). This produced total civilian radiation exposures amounting to 89 million person-rads of thyroid tissue exposure (about 24% of all exposure due to continental nuclear tests). This can be expected to eventually cause about 28,000 cases of thyroid cancer, leading to some 1400 deaths. Chart of fallout exposures from "underground tests" (61 K, 539x577). From National Cancer Institute Study Estimating Thyroid Doses of I-131 Received by Americans From Nevada Atmospheric Nuclear Bomb Test, 1997.

Source: http://nuclearweaponarchive.org/Usa/Tests/Upshotk.html