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.
Radiophobia
This incident, due to the era of secrecy around nuclear weapons, created widespread fear of uncontrolled and unpredictable nuclear weapons, and also of radioactively contaminated fish affecting the Japanese food supply. With the publication of Joseph Rotblat's findings that the contamination caused by the fallout from the Castle Bravo test was nearly a thousand times greater than that stated officially, outcry in Japan reached such a level that the incident was dubbed by some as "a second Hiroshima". To prevent the subsequent strong anti-nuclear movement from turning into an anti-American movement, the Japanese and U.S. governments agreed on compensation of 2 million dollars for the contaminated fishery, with the surviving 22 crew men receiving about ¥ 2 million each, ($5,556 in 1954, $ in 2022)