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Hiroshima and Nagasaki, bombings of (1945). The atomic bombing of the Japanese cities of Hiroshima and Nagasaki in August 1945 represents arguably the most important and most sinister development in warfare in the 20th century. By the early 1940s scientists in Britain and the USA were rapidly developing the technology that would lead to an atomic weapon. It was research conducted under the deepest secrecy for fear that Nazi scientists would be able to obtain the necessary data to enable them to produce a weapon of their own. In mid-1942 a programme code-named the Manhattan Project was set up to develop a bomb. The scheme involved 100, 000 persons and took three years to complete. On 16 July 1945 the first atomic bomb was tested at a site called Trinity in New Mexico. The blast that resulted was the release of energy equivalent to 20 kilotons of TNT. The steel tower on which the device was mounted completely vaporized, and the sand around melted to glass.

Hiroshima became the target of the first weapon at 08.15 on 6 August 1945. The all-clear had in fact sounded from an initial alert when the bomb was dropped. It was carried by a B-29 Superfortress called Enola Gay, and exploded about 602 yards (550 metres) over the city producing the equivalent of 15 kilotons of energy. Eyewitnesses reported seeing a parachute falling followed by a blast of intense heat. Between 130, 000 and 200, 000 people died, were injured, or disappeared. The Japanese government attempted to play down the impact and significance of this ominous development, which was followed a few days later by a second atomic bombing. This weapon had been destined for Kokura on the southern Japanese island of Kyushu, but cloud cover forced the crew to attack their secondary target of the shipyards of Nagasaki. The Nagasaki bomb was of about 20 kilotons but did less damage because of the local topography. It exploded above Urakami to the north of the port.

The injuries and destruction from the two bombs resulted from three factors: the intense blast, similar to that from conventional weapons but on a much larger scale; thermal radiation causing burns and producing fires; and nuclear radiation, which caused death and injury from damaged tissues. Each of the three effects was found on victims within 1 mile (1.6 km) from the epicentre, but the first two factors caused most deaths.

Even though more people died in the conventional bombing of Tokyo, the atomic bombings were significant because they caused death on a huge scale from one bomb dropped by one plane. Hiroshima and Nagasaki remain potent symbols and a sterile controversy over the use of the atomic weapons continues. In purely military terms the bombs proved decisive in persuading the Japanese government to think the unthinkable and accept defeat.

(1945)

The U.S. Army Air Forces' (USAAF) mission to use atomic bombs began in mid‐1944 when Gen. “Hap” Arnold, USAAF commander, initiated a special force to deliver a new “heavy and bulky” superweapon. He appointed Col. Paul W. Tibbets, a veteran of the first B‐17 mission over Europe, to command the 509th Composite Group, built around the 393rd Bombardment Squadron, commanded by Maj. Charles W. Sweeney. To accommodate the bomb, Tibbets had his B‐29s stripped of most defensive armaments. Most crew training took place at Wendover Field, Utah. The lead aircraft, flown by Tibbets, was a new B‐29, which he named the Enola Gay after his mother.

By mid‐1945, Manhattan Project scientists produced two kinds of atomic bombs: a gun type, detonated by firing one mass of uranium down a cylinder into another mass to create a self‐sustaining chain reaction; and an implosion bomb, which detonated when a volatile outer shell drove a layer of plutonium inward to collapse into a plutonium core and form a critical mass.

On 16 July 1945, as President Harry S. Truman began meeting with Soviet leader Josef Stalin and British prime minister Winston S. Churchill at the Potsdam Conference, Manhattan Project officials oversaw the first successful test of a nuclear weapon at Trinity Site, Alamogordo, New Mexico. Debate had already begun as to the wisdom and morality of using the bomb. It came to a choice between demonstrating the bomb (e.g., by destroying an island in Tokyo Bay), or obliterating an actual city. A panel of scientists concluded that saving American lives outweighed all other considerations and that no effective demonstration was feasible.

During the Potsdam Conference, Arnold argued that USAAF raids over Japan could end the war. Army Chief of Staff Gen. George C. Marshall worried that conventional bombing could not defeat such a determined enemy and would require an invasion of Japan. Marshall's view reinforced Secretary of War Henry L. Stimson's view and Truman's own belief that the bomb should be dropped before the U.S. invasion, scheduled for November 1945.

After informing Churchill and providing a vague reference about the weapon to Stalin, Truman issued a warning to Japan to surrender. Tokyo did not respond to the offer because the Japanese leaders were deeply divided. Some saw no alternative to surrender, while others wanted peace but feared for Emperor Hirohito's safety. A small faction advocated fighting to the death. There were deluded hopes that the Soviet Union might mediate for Japan. These notions created official paralysis. On 30 July, Truman approved the use of the atomic bomb.

On 3 August 1945, orders were issued to drop the first bomb when weather permitted. Operations began at 2:45 A.M., 6 August, as the Enola Gay and two observation B‐29s launched from Tinian. The primary target was Hiroshima, an industrial city that had seldom been attacked. Of little military significance, the city of 250,000 provided a good test of the bomb's destructiveness.

At 8:15 A.M. local time, the Enola Gay dropped the gun‐type uranium device, nicknamed “Little Boy,” from 31,600 feet. It detonated in the center of the city fifty seconds later. A 20,000‐foot mushroom cloud of smoke and debris whirled upward. At its base, a combination of blast, fire, and lethal radiation killed at least 60,000 civilians and several thousand military personnel; subsequently another 60,000 fatalities resulted from injuries or radiation poisoning. It also destroyed 81 percent of the city's structures.

When the Japanese government remained deadlocked, U.S. officials authorized the use of a second bomb. The primary target for the plutonium, implosion bomb, nicknamed “Fat Man,” was Kokura, a steel manufacturing center. Major Sweeney, who had flown his observation B‐29, The Great Artiste, during the Hiroshima raid, led the second mission. Without time to restore his plane to a bombing configuration, Sweeney switched planes with Capt. Frederick C. Bock, taking off in Bock's Car around 3:30 A.M. on 9 August. Sweeney found Kokura obscured by clouds and turned to a secondary target, Nagasaki, a seaport. At 10:58 A.M. local time, the bomb was dropped from 28,900 feet. It exploded two miles wide of the target because of the bombardier's reliance on radar until, when the clouds broke at the last minute, he returned to visual aiming. Because Nagasaki lay among hills surrounding the bay, whereas Hiroshima sat on a plain, parts of the city of 200,000 were sheltered from the blast. Still, at least 35,000 persons were killed. Afterwards, 40,000 more died from radiation and other injuries. Nearly half of the city's buildings were destroyed.

On 8 August, Soviet forces had overrun Japanese defenses in Manchuria, and with this and the atomic bombing, Emperor Hirohito concluded that the situation was hopeless. While still uncertain of his future, he chose to seek peace, thus invoking the moral authority of his office and defying the tradition that made the emperor a spokesman for his ministers rather than a ruler. After resistance by a few obsessed by the humiliation of surrender, he prevailed. This debate took time, and U.S. officials believed progress toward peace had failed. Truman ordered the resumption of conventional bombing on 14 August, with more than 1,000 B‐29s attacking Japan. As the B‐29s returned, Truman announced that the war was over. That same evening, Japan surrendered unconditionally, with official ceremonies held aboard the USS Missouri on 2 September, in Tokyo Bay.

The controversy over the use of the atomic bombs emerged during the Cold War as the world agonized over the possibility of a nuclear holocaust. In 1994–95, the debate focused on the nature of a planned exhibit of the Enola Gay at the Smithsonian Institution's Air and Space Museum in connection with the fiftieth anniversary of the bombing.

The atomic bomb has had a profound effect, ushering in the Cold War and the proliferation of nuclear weapons. Thus far, the era has also shown ostensibly that there is a point beyond which mankind will not go. Today, civili zation's greatest challenge is to make sure that the atomic bombings of Hiroshima and Nagasaki remain singular events.