On August 6, 1945, during World War II (1939-45), an American B-29 bomber dropped the world’s first deployed atomic bomb over the Japanese city of Hiroshima. The explosion immediately killed an estimated 80,000 people; tens of thousands more would later die of radiation exposure. Three days later, a second B-29 dropped another A-bomb on Nagasaki, killing an estimated 40,000 people. Japan’s Emperor Hirohito announced his country’s unconditional surrender in World War II in a radio address on August 15, citing the devastating power of “a new and most cruel bomb.”
The Manhattan Project
Even before the outbreak of war in 1939, a group of American scientists—many of them refugees from fascist regimes in Europe—became concerned with nuclear weapons research being conducted in
Nazi Germany. In 1940, the U.S. government began funding its own atomic weapons development program, which came under the joint responsibility of the Office of Scientific Research and Development and the War Department after the U.S. entry into
World War II. The U.S. Army Corps of Engineers was tasked with spearheading the construction of the vast facilities necessary for the top-secret program, codenamed “The
Manhattan Project” (for the engineering corps’ Manhattan district).