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The United States, with assistance from the United Kingdom and Canada,[5] designed and built the first atomic bombs under what was called the Manhattan Project. The scientific research was directed by American physicist J. Robert Oppenheimer. The Hiroshima bomb, a gun-type bomb called "Little Boy", was made with uranium-235, a rare isotope of uranium. The atomic bomb was first tested at Trinity Site, on July 16, 1945, near Alamogordo, New Mexico. The test weapon, "the gadget," and the Nagasaki bomb, "Fat Man", were both implosion-type devices made primarily of plutonium-239, a synthetic element.[6]
Choice of targets
Although many political and military leaders, including General Eisenhower, argued against dropping the bombs on civilian targets, the Target Committee seemed to have few qualms about using them on civilian targets.[citation needed]
Map showing the locations of Hiroshima and Nagasaki, Japan where the two atomic weapons were employedThe Target Committee at Los Alamos on May 10–11, 1945, recommended Kyoto, Hiroshima, Yokohama, and the arsenal at Kokura as possible targets. Hiroshima was described as "This is 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 focussing effect which would considerably increase the blast damage. Due to rivers it is not a good incendiary target." The Target Committee stated that "It was agreed that psychological factors in the target selection were of great importance. Two aspects of this are (1) obtaining the greatest psychological effect against Japan and (2) making the initial use sufficiently spectacular for the importance of the weapon to be internationally recognized when publicity on it is released. In this respect Kyoto has the advantage of the people being more highly intelligent and hence better able to appreciate the significance of the weapon. Hiroshima has the advantage of being such a size and with possible focussing from nearby mountains that a large fraction of the city may be destroyed. The Emperor's palace in Tokyo has a greater fame than any other target but is of least strategic value."[7]
During World War II, Edwin O. Reischauer was the Japan expert for the U.S. Army Intelligence Service, where he is said to have prevented the bombing of Kyoto during the war,[8] as explained by Robert Jungk in Brighter Than a Thousand Suns: A personal history of the atomic scientists:
"On the short list of targets for the atom bomb, in addition to Hiroshima, Kokura and Niigata, was the Japanese city of temples, Kyoto. When the expert on Japan, Professor Edwin O. Reischauer, heard this terrible news, he rushed into the office of his chief, Major Alfred MacCormack, in a department of the Army Intelligence Service. The shock caused him to burst into tears. MacCormack, a cultivated and humane New York lawyer, thereupon managed to persuade Secretary of War Stimson to reprieve Kyoto and have it crossed off the black list."[9]
In his autobiography, Reischauer specifically refuted the validity of this broadly-accepted version:
"I probably would have done this if I had ever had the opportunity, but there is not a word of truth to it. As has been amply proved by my friend Otis Cary of Doshisha in Kyoto, the only person deserving credit for saving Kyoto from destruction is Henry L. Stimson, the Secretary of War at the time, who had known and admired Kyoto ever since his honeymoon there several decades earlier."[10]
The Potsdam ultimatum
On July 26, Truman and other allied leaders issued The Potsdam Declaration outlining terms of surrender for Japan. It was presented as an ultimatum and stated that without a surrender, the Allies would attack Japan, resulting in "the inevitable and complete destruction of the Japanese armed forces and just as inevitably the utter devastation of the Japanese homeland" but the atomic bomb was not mentioned. On July 28, Japanese papers reported that the declaration had been rejected by the Japanese government. That afternoon, Prime Minister Kantaro Suzuki declared at a press conference that the Potsdam Declaration was no more than a rehash (yakinaoshi) of the Cairo Declaration and that the government intended to ignore it (mokusatsu).[11] The statement was taken by both Japanese and foreign papers as a clear rejection of the declaration. Emperor Hirohito, who was waiting for a Soviet reply to noncommittal Japanese peace feelers made no move to change the government position.[12] On July 31, he made clear to Kido that the Imperial Regalia of Japan had to be defended at all costs.[13]
In early July, on his way to Potsdam, Truman had re-examined the decision to use the bomb. In the end, Truman made the decision to drop the atomic bombs on Japan. His stated intention in ordering the bombings was to bring about a quick resolution of the war by inflicting destruction, and instilling fear of further destruction, that was sufficient to cause Japan to surrender.[14]
Hiroshima
Hiroshima during World War II
At the time of its bombing, Hiroshima was a city of some industrial and military significance. A number of military camps were located nearby, including the headquarters of the Fifth Division and Field Marshal Shunroku Hata's 2nd General Army Headquarters, which commanded the defense of all of southern Japan. Hiroshima was a minor supply and logistics base for the Japanese military. The city was a communications center, a storage point, and an assembly area for troops. It was one of several Japanese cities left deliberately untouched by American bombing, allowing a pristine environment to measure the damage caused by the atomic bomb. Another account stresses that after General Spaatz reported that Hiroshima was the only targeted city without prisoner of war (POW) camps, Washington decided to assign it highest priority[citation needed].
A postwar "Little Boy" casing mockupThe center of the city contained several reinforced concrete buildings and lighter structures. Outside the center, the area was congested by a dense collection of small wooden workshops set among Japanese houses. A few larger industrial plants lay near the outskirts of the city. The houses were of wooden construction with tile roofs, and many of the industrial buildings also were of wood frame construction. The city as a whole was highly susceptible to fire damage.[citation needed]
In front of the harbor of the city, on the island of Okunoshima, was a toxic gas factory linked to Unit 731.[15] Different types of chemical weapons were produced there during the first part of the Sh?wa era like mustard gas, yperite, lewisite and cyanide.[16]
The population of Hiroshima had reached a peak of over 381,000 earlier in the war, but prior to the atomic bombing the population had steadily decreased because of a systematic evacuation ordered by the Japanese government. At the time of the attack the population was approximately 255,000. This figure is based on the registered population used by the Japanese in computing ration quantities, and the estimates of additional workers and troops who were brought into the city may be inaccurate.
Seizo Yamada's ground level photo taken from approximately 7 km northeast of Hiroshima.
The bombing
For the composition of the USAAF mission see 509th Composite Group.
Hiroshima was the primary target of the first nuclear bombing mission on August 6, with Kokura and Nagasaki being alternative targets. August 6 was chosen because there had previously been cloud cover over the target. The 393d Bombardment Squadron B-29 Enola Gay, piloted and commanded by 509th Composite Group commander Colonel Paul Tibbets, was launched from North Field airbase on Tinian in the West Pacific, about six hours flight time from Japan. The Enola Gay (named after Colonel Tibbets' mother) was accompanied by two other B29s, The Great Artiste which carried instrumentation, commanded by Major Charles W. Sweeney, and a then-nameless aircraft later called Necessary Evil (the photography aircraft) commanded by Captain George Marquardt.[17]
After leaving Tinian the aircraft made their way separately to Iwo Jima where they rendezvoused at 2440 m (8000 ft) and set course for Japan. The aircraft arrived over the target in clear visibility at 9855 m (32,000 ft). On the journey, Navy Captain William Parsons had armed the bomb, which had been left unarmed to minimize the risks during takeoff. His assistant, 2nd Lt. Morris Jeppson, removed the safety devices 30 minutes before reaching the target area.[17]
Hiroshima, in the aftermath of the bombingThe release at 08:15 (Hiroshima time) was uneventful, and the gravity bomb known as "Little Boy", a gun-type fission weapon with 60 kg (130 pounds) of uranium-235, took 57 seconds to fall from the aircraft to the predetermined detonation height about 600 meters (1,900 ft) above the city. It created a blast equivalent to about 13 kilotons of TNT. (The U-235 weapon was considered very inefficient, with only 1.38% of its material fissioning.)[18] The radius of total destruction was about 1.6 km (1 mile), with resulting fires across 11.4 km² (4.4 square miles).[19] Infrastructure damage was estimated at 90 percent of Hiroshima's buildings being either damaged or completely destroyed.
About an hour before the bombing, Japanese early warning radar detected the approach of some American aircraft headed for the southern part of Japan. An alert was given and radio broadcasting stopped in many cities, among them Hiroshima. At nearly 08:00, the radar operator in Hiroshima determined that the number of planes coming in was very small
