The main purpose of the U.S. atomic bombings of Hiroshima and Nagasaki in August 1945 was to bring a swift end to World War II. Faced with the prospect of a costly invasion of the Japanese mainland, U.S. officials believed that using atomic bombs would compel Japan to surrender unconditionally. The bomb dropped on Hiroshima on August 6 killed tens of thousands immediately, with many more succumbing to radiation and injuries. Three days later, a second bomb was dropped on Nagasaki. Japan announced its surrender shortly afterward, leading to the conclusion of the war but raising ethical concerns regarding nuclear warfare.