Mark 21 nuclear bomb
The Mark 21 nuclear bomb was a United States nuclear gravity bomb first produced in 1955. It was based on the TX-21 "Shrimp" prototype that had been detonated during the Castle Bravo test in March 1954. While most of the Operation Castle tests were intended to evaluate weapons intended for immediate stockpile, or which were already available for use as part of the Emergency Capability Program, Castle Bravo was intended to test a design which would drastically reduce the size and costs of the first generation of air-droppable atomic weapons (the Mk 14, Mk 17 & Mk 24). At long, in diameter, and weighing , the Mk-21 was half the length and one-third the weight of the Mk-17/24 weapons it replaced. Its minimum yield was specified at four megatons.
Nuclear testing at Bikini Atoll
On the Marshall Islands, the detonation of Castle Bravo was the cause of most of the radiation exposure to the surrounding populations. The fallout levels attributed to the Castle Bravo test are the highest in history. The exposure to fallout has been linked to increase the likelihood of several types of cancer such as leukemia and thyroid cancer. The relationship between I-131 levels and thyroid cancer is continuing to be researched. There are also correlations between fallout exposure levels and diseases such as thyroid disease like hypothyroidism. Populations of the Marshall Islands that received significant exposure to radionuclides have a much greater risk of developing cancer. The Castle Bravo test detonation produced an explosion of approximately 15 megatons, which is about three times its predicted value. Populations neighboring the test site were exposed to high levels of radiation resulting in mild radiation sickness of many (nausea, vomiting, diarrhea). Several weeks later, many people began suffering from alopecia (hair loss) and skin lesions as well. The female population of the Marshall Islands have a sixty times greater cervical cancer mortality than a comparable mainland United States population. The Islands populations also have a five time greater likelihood of breast or gastrointestinal mortality, and lung cancer mortality is three times higher than the mainland population. The male population on the Marshall Islands lung cancer mortality is four times greater than the overall United States rates, and the oral cancer rates are ten times greater.