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.
History of the Marshall Islands
From 1946 to 1958, the early years of the Cold War, the United States tested 67 nuclear weapons at its Pacific Proving Grounds located in the Marshall Islands, including the largest atmospheric nuclear test ever conducted by the U.S., code named Castle Bravo. "The bombs had a total yield of 108,496 kilotons, over 7,200 times more powerful than the atomic weapons used during World War II." With the 1952 test of the first U.S. hydrogen bomb, code named "Ivy Mike," the island of Elugelab in the Enewetak atoll was destroyed. In 1956, the United States Atomic Energy Commission regarded the Marshall Islands as "by far the most contaminated place in the world."