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.
Alvin C. Graves
Graves became dismissive of the radiation risks from nuclear testing while serving as test director for the Nevada Test Site shots during the 1950s. He announced that the risks from fallout were "concocted in the minds of weak malingerers." As a spokesman for the Nevada Test Site, he spoke in local areas around Nevada assuring the population of no danger from the activities there. As the head of the Los Alamos Laboratory's J (Test) Division, he was the scientific director or deputy director of most of the nuclear tests from 1948 through the 1950s, including the Desert Rock exercises which exposed military personnel to radiation, and the Castle Bravo test that irradiated many native islanders and test personnel. Asked to testify before the Joint Committee on Atomic Energy on the danger of radiation causing cancer, Graves replied: