In August 1945, the United States dropped two atomic bombs on the Japanese cities of Hiroshima and Nagasaki, respectively. Developed under the top-secret Manhattan Project, these were the first and only uses of nuclear weapons in armed conflict. The Hiroshima bomb, 'Little Boy,' was a uranium-based weapon, while the Nagasaki bomb, 'Fat Man,' used plutonium. The blasts and subsequent radiation killed an estimated 110,000 to 210,000 people, most of whom were civilians. Six days after the Nagasaki bombing, Japan announced its unconditional surrender, effectively ending World War II. The events remain highly debated; proponents argue they prevented a costly ground invasion of Japan, while critics point to the immense civilian suffering and the ethical implications of nuclear warfare. These bombings ushered in the Atomic Age and the nuclear arms race of the Cold War.