On August 31, 1957, Operation Plumbob’s “Smoky” test flamed into the sky over busy Yucca Flat, 65 miles north of Las Vegas. Area 8 of the Nevada Test Site played host that day to the third test of the UCRL TX-41 – a three-stage, thermonuclear weapon design. After two previous tests of 3.5 and 5.0 megatons (Redwing Zuni and Tewa), “Smoky” was probably a partial, two-stage test with a decreased yield of 45-50 kilotons. The MK-41 nuclear device eventually developed from the TX-41 test series became the largest-yield nuclear weapon ever developed or deployed by the United States. Its yield of 25 megatons was also the highest yield-to-weight ratio for a US nuclear weapon, at about 6 kilotons per kilogram.
Smoky became famous – notorious, even – for its tragic consequences. Over three thousand servicemen had been in the vicinity of ground zero shortly after the blast, practicing maneuvers as part of the Desert Rock exercise. Their exposure to radiation from the test eventually became the subject of a Congressional investigation and epidemiological evaluation. A 1980 study found statistically significant increases in leukemia cases among the 3224 participants. Instead of the expected four cases, ten were found.