After the Japanese rejected the U.S. demand for unconditional surrender in the spring on 1945, Harry Truman, the U.S. President authorized the use of atomic weapons in Japan. The Manhattan project had produced two nuclear weapons by that time, one based on uranium known as Little Boy and the other based on plutonium named Fat Man.
The goal for dropping an atomic bomb on a Japanese city was to force surrender according to the Potsdam Declaration. The psychological impact on the Japanese was especially important. In addition, the United States wanted other nations to recognize the importance of this new weapon when news of the devastation was made public.
The choice of targets had three constraints.
- The target had to be more than three miles in diameter and had to be an important target in a large urban area.
- The detonation of the bomb would result in significant damage to the target
- The target was unlikely to be attacked by August of 1945.
Four potential targets were initially selected that met the required criteria including Kokura, Hiroshima, Niigata and Kyoto. Kyoto was dropped from the list of targets because of it importance to Japanese religion. Nagasaki was added to the list as a potential target to replace Kyoto. Leaflets had previously been dropped on Japanese cities warning of possible bombing raids.
Hiroshima was ultimately selected as a target for Little Boy. It was an important army depot and port of embarkation in the middle of an urban industrial area. Adjacent hills were expected to create a focusing effect to increase the damage of the blast. Nearby rivers made it a poor target for firebombing. Little Boy was dropped on Hiroshima on August 6, 1945 and exploded.
Kokura was the first selection from the primary list as the target for the Fat Man bomb. It was felt that the distance to Niigata was too great for a successful mission. Nagasaki had already been bombed a number of times and it was spread out over hills and valleys which could dissipate the force of a big blast. The bomber carrying the Fat Man bomb took off on August 9, 1945 with the intention of dropping the bomb on the city of Kokura. However, the day was cloudy and after three passes over the city without being able to sight the target, the mission to bomb Kokura was aborted. This was fortunate for a few thousand American and Dutch prisoners of war who were being held at Kokura.
Nagasaki was chosen as a target only after the attack on Kokura was aborted. The bomber, low on fuel, turned south and headed for Nagasaki. The weather was clear and the Fat Man bomb was dropped and exploded. With the explosion of these two nuclear bombs in Japanese cities, the United States became the first and, to date, only country on earth to use nuclear weapons against another country.
