Operation Castle was a series of nuclear tests conducted by the United States in 1954. The tests were part of the larger Operation Upshot-Knothole and aimed to evaluate the effects of thermonuclear weapons. The most notable test, Castle Bravo, resulted in a significant yield, far exceeding expectations, and caused widespread radioactive contamination. The operation took place at the Bikini Atoll in the Marshall Islands. It involved multiple detonations, including tests of new bomb designs. The fallout from Castle Bravo affected nearby islands and led to health concerns for local populations, highlighting the dangers of nuclear testing and its environmental impact.