Castle Bravo was the code name for the first test of a thermonuclear weapon by the United States, conducted on March 1, 1954. It took place at Bikini Atoll in the Marshall Islands and was part of a series of nuclear tests known as Operation Castle. The explosion yielded about 15 megatons of TNT, making it the most powerful nuclear device detonated by the U.S. at that time. The test resulted in significant radioactive fallout, affecting nearby islands and the local population. The unexpected size of the explosion led to increased scrutiny of nuclear testing and raised concerns about the environmental and health impacts of nuclear weapons.