Consequently, Truman approved the long-standing plans for the US Army Air Force to drop atomic bombs on a list of preselected Japanese cities. The list of targets excluded Tokyo and Kyoto because of their political and historic importance. Instead, the intended target of the first bomb was Hiroshima, a fan-shaped city of approximately 550,000 people that occupied the estuary of the Ota River. The city was also home to the headquarters of the Japanese army that defended the island of Kyushu as well as a number of war industries.
On 6 and 9 August 1945, the United States detonated two atomic bombs over the Japanese cities of Hiroshima and Nagasaki respectively. The bombings killed between 129,000 and 226,000 people, most of whom were civilians, and remain the only use of nuclear weapons in an armed conflict. Japan surrendered to the Allies on 15 August, six days after the bombing of Nagasaki and the Soviet Union's declaration of war against Japan and invasion of Japanese-occupied Manchuria. The Japanese government signed the instrument of surrender on 2 September, effectively ending the war.
In the final year of World War II, the Allies prepared for a costly invasion of the Japanese mainland. This undertaking was preceded by a conventional bombing and firebombing campaign that devastated 64 Japanese cities. The war in the European theatre concluded when Germany surrendered on 8 May 1945, and the Allies turned their full attention to the Pacific War. By July 1945, the Allies' Manhattan Project had produced two types of atomic bombs: "Little Boy", an enriched uranium gun-type fission weapon, and "Fat Man", a plutonium implosion-type nuclear weapon. The 509th Composite Group of the United States Army Air Forces was trained and equipped with the specialized Silverplate version of the Boeing B-29 Superfortress, and deployed to Tinian in the Mariana Islands. The Allies called for the unconditional surrender of the Imperial Japanese armed forces in the Potsdam Declaration on 26 July 1945, the alternative being "prompt and utter destruction". The Japanese government ignored the ultimatum.
The consent of the United Kingdom was obtained for the bombing, as was required by the Quebec Agreement, and orders were issued on 25 July by General Thomas Handy, the acting chief of staff of the United States Army, for atomic bombs to be used against Hiroshima, Kokura, Niigata, and Nagasaki. These targets were chosen because they were large urban areas that also held militarily significant facilities. On 6 August, a Little Boy was dropped on Hiroshima. Three days later, a Fat Man was dropped on Nagasaki. Over the next two to four months, the effects of the atomic bombings killed between 90,000 and 146,000 people in Hiroshima and 60,000 and 80,000 people in Nagasaki; roughly half occurred on the first day. For months afterward, many people continued to die from the effects of burns, radiation sickness, and injuries, compounded by illness and malnutrition. Though Hiroshima had a sizable military garrison, most of the dead were civilians.
Scholars have extensively studied the effects of the bombings on the social and political character of subsequent world history and popular culture, and there is still much debate concerning the ethical and legal justification for the bombings. Supporters claim that the atomic bombings were necessary to bring an end to the war with minimal casualties; critics believe that the bombings were unnecessary for the war's end and a war crime, and highlight the moral and ethical implications of the intentional nuclear attack on civilians.
In 1945, the Pacific War between the Empire of Japan and the Allies entered its fourth year. Most Japanese military units fought fiercely, ensuring that the Allied victory would come at an enormous cost. The 1.25 million battle casualties incurred in total by the United States in World War II included both military personnel killed in action and wounded in action. Nearly one million of the casualties occurred during the last year of the war, from June 1944 to June 1945. In December 1944, American battle casualties hit an all-time monthly high of 88,000 as a result of the German Ardennes Offensive. Worried by the losses sustained, President Roosevelt suggested the use of atomic bombs on Germany as soon as possible, but was informed the first usable atomic weapons were still months away.[1] America's reserves of manpower were running out. Deferments for groups such as agricultural workers were tightened, and there was consideration of drafting women. At the same time, the public was becoming war-weary, and demanding that long-serving servicemen be sent home.[2]
While the United States had developed plans for an air campaign against Japan prior to the Pacific War, the capture of Allied bases in the western Pacific in the first weeks of the conflict meant that this offensive did not begin until mid-1944 when the long-ranged Boeing B-29 Superfortress became ready for use in combat.[22] Operation Matterhorn involved India-based B-29s staging through bases around Chengdu in China to make a series of raids on strategic targets in Japan.[23] This effort failed to achieve the strategic objectives that its planners had intended, largely because of logistical problems, the bomber's mechanical difficulties, the vulnerability of Chinese staging bases, and the extreme range required to reach key Japanese cities.[24]
The Japanese military was unable to stop the Allied attacks and the country's civil defense preparations proved inadequate. Japanese fighters and anti-aircraft guns had difficulty engaging bombers flying at high altitude.[45] From April 1945, the Japanese interceptors also had to face American fighter escorts based on Iwo Jima and Okinawa.[46] That month, the Imperial Japanese Army Air Service and Imperial Japanese Navy Air Service stopped attempting to intercept the air raids to preserve fighter aircraft to counter the expected invasion.[47] By mid-1945 the Japanese only occasionally scrambled aircraft to intercept individual B-29s conducting reconnaissance sorties over the country, to conserve supplies of fuel.[48] In July 1945, the Japanese had 137,800,000 litres (1,156,000 US bbl) of avgas stockpiled for the invasion of Japan. About 72,000,000 litres (604,000 US bbl) had been consumed in the home islands area in April, May and June 1945.[49] While the Japanese military decided to resume attacks on Allied bombers from late June, by this time there were too few operational fighters available for this change of tactics to hinder the Allied air raids.[50]
The 509th Composite Group was constituted on 9 December 1944, and activated on 17 December 1944, at Wendover Army Air Field, Utah, commanded by Colonel Paul Tibbets.[59] Tibbets was assigned to organize and command a combat group to develop the means of delivering an atomic weapon against targets in Germany and Japan. Because the flying squadrons of the group consisted of both bomber and transport aircraft, the group was designated as a "composite" rather than a "bombardment" unit.[60] Due to its remoteness, Tibbets selected Wendover for his training base over Great Bend, Kansas and Mountain Home, Idaho.[61] Each bombardier completed at least 50 practice drops of inert or conventional explosive pumpkin bombs, targeting islands around Tinian and later the Japanese home islands, until as late as August 14, 1945.[62][63] Some of the missions over Japan were flown by single unescorted bombers with a single payload in order to accustom the Japanese to this pattern. They also simulated actual atomic bombing runs, including the directions of ingress and egress with respect to the wind. Tibbets himself was barred from flying most missions over Japan for fear that he might be captured and forced to reveal what he knew.[63] On 5 April 1945, the code name Operation Centerboard was assigned. The officer responsible for its allocation in the War Department's Operations Division was not cleared to know any details of it. The first bombing was later codenamed Operation Centerboard I, and the second, Operation Centerboard II.[64]
These cities were largely untouched during the nightly bombing raids, and the Army Air Forces agreed to leave them off the target list so accurate assessment of the damage caused by the atomic bombs could be made. Hiroshima was described as "an important army depot and port of embarkation in the middle of an urban industrial area. It is a good radar target and it is such a size that a large part of the city could be extensively damaged. There are adjacent hills which are likely to produce a focusing effect which would considerably increase the blast damage. Due to rivers it is not a good incendiary target."[72]
In early May 1945, the Interim Committee was created by Stimson at the urging of leaders of the Manhattan Project and with the approval of Truman to advise on matters pertaining to nuclear technology.[81] They agreed that the atomic bomb was to be used (1) against Japan at the earliest opportunity, (2) without special warning, and (3) on a "dual target" of military installation surrounded by other buildings susceptible to damage.[63]
It was evident that everyone would suspect trickery. If a bomb were exploded in Japan with previous notice, the Japanese air power was still adequate to give serious interference. An atomic bomb was an intricate device, still in the developmental stage. Its operation would be far from routine. If during the final adjustments of the bomb the Japanese defenders should attack, a faulty move might easily result in some kind of failure. Such an end to an advertised demonstration of power would be much worse than if the attempt had not been made. It was now evident that when the time came for the bombs to be used we should have only one of them available, followed afterwards by others at all-too-long intervals. We could not afford the chance that one of them might be a dud. If the test were made on some neutral territory, it was hard to believe that Japan's determined and fanatical military men would be impressed. If such an open test were made first and failed to bring surrender, the chance would be gone to give the shock of surprise that proved so effective. On the contrary, it would make the Japanese ready to interfere with an atomic attack if they could. Though the possibility of a demonstration that would not destroy human lives was attractive, no one could suggest a way in which it could be made so convincing that it would be likely to stop the war.[83]
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