In August 1945, during World War II, America dropped two atomic bombs in the space of three days over Hiroshima and Nagasaki, immediately killing over 120,000 people.
The Manhattan Project
Before the outbreak of war in 1939, a group of American scientists became concerned with nuclear weapons research being carried out in Nazi Germany. The US started funding its own atomic weapons development program in 1940, which came under the joint management of the War Department and the Office of Scientific Research and Development after US entered into World War II. The US Army Corps was given the responsibility of spearheading the construction of huge facilities needed for the top-secret program, codenamed “The Manhattan Project.”
During the next several years, the program’s scientists worked on making the crucial materials for plutonium (Pu-239) and nuclear fission-uranium-235. On the morning of July 16 1945, the Manhattan Project held its first victorious test of an atomic device, in New Mexico.
The Japanese will not surrender
The Allied powers had already defeated Germany in Europe by the time of the test. However, Japan declared that they would fight until the very end in the Pacific, even though there were clear indications that they had little possibility of winning. Between mid-April 1945 and mid-July, Japanese forces caused Allied casualties totaling almost half those suffered in three years of war in the Pacific. This was evidence that Japan had become even more dangerous when faced with defeat. Japan’s government declined the Allied demand for surrender in late July and implemented the Potsdam Declaration, which threatened Japan with total and prompt destruction if they refused.
In order to avoid US casualties, President Truman decided to use the atomic bomb in the hopes of bringing the war to a speedy end.
“Little boy” and “Fat man”
Hiroshima was chosen as the first target. A plane dropped the bomb – called “little man” – at 8:15 in the morning by parachute, and it exploded 2,000 feet above Hiroshima, destroying five square miles of the city.
However, the Japanese did not surrender, and on August 9 the plutonium bomb “fat man” was dropped over Nagasaki, the secondary target, at 11:02 in the morning. This bomb was more powerful than the one used on Hiroshima, but Nagasaki’s topography limited the destruction to 2.6 square miles.
Emperor Hirohito announced Japan’s surrender at noon on August 15, 1945. The official surrender agreement was signed on September 2 about Missouri – a US battleship – anchored in Tokyo Bay.