The atomic bombing of Hiroshima

At 8.15 a.m. local time on 6 August 1945 the American B-29 bomber Enola Gay, flown by Colonel Paul Tibbets, dropped the uranium bomb Little Boy on Hiroshima. After falling for some 43–44 seconds, the bomb exploded roughly 600 metres above the city centre with a yield usually estimated at about 15 kilotons of TNT. In a fraction of a second it wiped out the heart of a city that then had some 340,000–350,000 inhabitants, and the fires it started consumed whatever the blast wave had left standing. It was the first attack with a nuclear weapon in history.

The statement that the Enola Gay dropped “the first atomic bomb” needs one qualification: the first nuclear device had been detonated three weeks earlier, on 16 July, at a test site in New Mexico, but that was a plutonium bomb of a different design. Little Boy was the first nuclear bomb used in warfare – and the first uranium bomb ever to explode, since a weapon of this type had never been tested.

By the end of 1945, according to various estimates, between about 70,000 and about 140,000 people had died as a result of the explosion, the overwhelming majority of them civilians. Sixteen hours after the attack the White House announced that an atomic bomb had been dropped on Hiroshima and threatened Japan with a “rain of ruin from the air” if it did not accept the terms of the Potsdam Declaration.

The weapon and the men

The bomb was the product of the Manhattan Project – the largest scientific and industrial undertaking of the war, directed by General Leslie Groves, with its laboratory at Los Alamos headed by Robert Oppenheimer. Little Boy was a “gun-type” bomb: inside a steel barrel a propellant charge fired one block of uranium-235 into another, creating a supercritical mass. It was about 3 metres long, weighed more than 4 tonnes and contained around 64 kilograms of uranium enriched at the Oak Ridge plants. Its designers were so confident in this simple arrangement that they dispensed with a test – in any case the entire stock of uranium was enough for only one bomb. Paradoxically, the weapon was highly inefficient: less than 2 per cent of its material underwent fission.

To deliver the bombs, a special unit was formed at Wendover, Utah, in December 1944 – the 509th Composite Group, commanded by the 29-year-old Lieutenant Colonel (from 1945 Colonel) Paul Tibbets, an experienced B-17 pilot over Europe and North Africa and later a B-29 test pilot. The group received specially modified “Silverplate” bombers and its own transport squadron; its crews practised dropping single heavy bombs and making a sharp 155-degree turn immediately afterwards to carry the aircraft away from the explosion. In the spring of 1945 the 509th Composite Group moved to North Field on Tinian in the Marianas, which the Americans had captured in the summer of 1944. From 20 July its crews flew practice missions over Japan, dropping conventional bombs with the shape and weight of the plutonium bomb, known as “pumpkins”.

Components of Little Boy reached Tinian on 26 July aboard the cruiser Indianapolis, which was sunk by a Japanese submarine a few days later; the remaining parts of the uranium charge were flown in. Assembly of the bomb was completed in early August.

Choosing the target and the order

In the spring of 1945 the Target Committee, made up of military officers and scientists, selected several Japanese cities that had so far been spared the incendiary raids waged since March by General Curtis LeMay’s B-29s – so that the effects of the new weapon could be measured. Secretary of War Henry Stimson insisted on striking Kyoto, the old imperial capital, from the list. On 1 June the Interim Committee, which advised Stimson on atomic weapons, recommended that the bomb be used as soon as possible, without warning, against war plants surrounded by housing. Proposals from some scientists – set out in the so-called Franck Report and in a petition by Leó Szilárd – that the bomb’s power should first be demonstrated on an uninhabited site were rejected.

Hiroshima was an important military centre: the castle housed the headquarters of Field Marshal Shunroku Hata’s Second General Army, responsible for the defence of western Japan; troops embarked at the port of Ujina; and the city had armaments factories. According to American estimates from 1946, some 24,000 soldiers were stationed there. At the same time it was a densely built city of wooden houses, whose inhabitants wondered why the bombers had so far passed them by.

On 25 July General Thomas Handy, acting Army Chief of Staff, sent the commander of the Strategic Air Forces in the Pacific, General Carl Spaatz, the order: the 509th Composite Group was to drop its first “special bomb” as soon as the weather permitted after about 3 August on one of the following targets: Hiroshima, Kokura, Niigata or Nagasaki. The day before, at Potsdam, Harry Truman had casually mentioned to Stalin “a new weapon of unusual destructive force”. The Potsdam Declaration was issued on 26 July, and on 28 July Prime Minister Kantarō Suzuki described the government’s attitude to it with the word mokusatsu. Bad weather delayed the mission by several days; on 4 August Tibbets briefed the crews, and on 5 August he named his aircraft after his mother – Enola Gay.

The flight of the Enola Gay

The Enola Gay took off from Tinian at 2.45 a.m. island time (1.45 a.m. Japanese time) with a crew of twelve. Captain Robert Lewis flew as co-pilot, Major Thomas Ferebee was the bombardier and Captain Theodore Van Kirk the navigator. Also on board was Navy Captain William “Deak” Parsons, the specialist responsible for arming the bomb and technical commander of the mission. Because several B-29s had crashed on take-off the previous night, Parsons decided to load the propellant charges into the bomb only once airborne; he did so shortly after take-off, and half an hour before the target his assistant, Lieutenant Morris Jeppson, removed the last safety devices.

An hour earlier three weather reconnaissance aircraft had taken off for Hiroshima, Kokura and Nagasaki. The Enola Gay was escorted by two B-29s: Major Charles Sweeney’s The Great Artiste, carrying measuring instruments, and Captain George Marquardt’s camera aircraft, later named Necessary Evil. The aircraft rendezvoused over Iwo Jima and headed for Japan. At around 7.25 a.m. the weather aircraft Straight Flush, flown by Captain Claude Eatherly, reported light cloud over Hiroshima and recommended attacking the primary target.

In Hiroshima the weather aircraft had triggered an air-raid alert at about 7.09 a.m., which was lifted at 7.31. When three more bombers appeared over the city at some 9,500 metres, many inhabitants were on their way to work, and schoolchildren mobilised to demolish houses for firebreaks were working in the open. The Japanese defences made no attempt to intercept so small a group.

8.15 a.m.

At 8.09 a.m. Tibbets began the bomb run, handing control to the bombardier. The aiming point was the Aioi Bridge, easily recognised from the air by its T shape. At 8.15 Ferebee released the bomb and Tibbets threw the aircraft into its sharp turn. Carried by a crosswind, Little Boy drifted some 240 metres off target and exploded over the Shima surgical hospital. Survivors remembered the flash – pika – and the roar – don. In its first instant the fireball reached a temperature of millions of degrees; within a kilometre of the hypocentre people in the open were killed by the heat almost instantly, and the blast wave flattened wooden houses for more than two kilometres around. When it reached the aircraft, by then more than ten kilometres away, the Enola Gay was violently jolted. The tail gunner, Sergeant George Caron, photographed the mushroom cloud rising over the city. The co-pilot, Robert Lewis, wrote in his flight notes a question later quoted in several versions: “My God, what have we done?”

The Enola Gay landed on Tinian in the afternoon. General Spaatz decorated Tibbets with the Distinguished Service Cross on the airfield apron.

The city after the explosion

American surveys found that about 12 square kilometres of the city had been destroyed. According to Japanese findings, some 69 per cent of buildings were destroyed and a further 6–7 per cent damaged. Within tens of minutes thousands of fires merged into a firestorm that raged through the city until evening. “Black rain” – droplets mixed with soot and radioactive dust – fell on the north-western districts.

The city’s services ceased to exist. The mayor, Senkichi Awaya, was killed. According to later figures, more than 90 per cent of the city’s doctors and a similar proportion of its nurses were killed or injured; the hospitals lay in ruins. In the castle courtyard, about 800 metres from the hypocentre, more than three thousand soldiers of the Second General Army were killed while doing their morning exercises. Among the mortally wounded staff officers was Lieutenant Colonel Yi U, a prince of the Korean royal family, who died the next day. The lightly wounded Field Marshal Hata took charge of the rescue effort. The first report of the city’s destruction by a “new type of bomb” was telephoned from the signals bunker in the castle by a fourteen-year-old schoolgirl mobilised for communications duty.

Radiation made itself felt over the following days and weeks. People who had survived the explosion with no visible injuries began to lose their hair, bleed from the gums and die of radiation sickness. Doctors did not know what they were dealing with.

The victims were not only Japanese. Tens of thousands of Koreans lived in Hiroshima, many of them brought there as forced labourers. Estimates of the number of Koreans killed vary widely: from around 5,000–8,000 in some studies to about 20,000 or more according to Korean victims’ organisations. Japanese Americans living in the city and prisoners of war were also killed. According to the research of the Japanese investigator Shigeaki Mori and American historians, twelve American airmen shot down at the end of July were being held in the military police jail, about 400 metres from the hypocentre; most died on the spot, and according to witnesses two who were badly injured were left by the military police near the Aioi Bridge, where they were beaten to death by a crowd.

How many died

The exact number of victims has never been established: records were destroyed, no one knows how many people were in the city that morning, and many died later of their injuries and of radiation. The Manhattan Project report of 1946 gave about 66,000 killed and 69,000 injured; the United States Strategic Bombing Survey (USSBS) gave 70,000–80,000 killed. Japanese recalculations from the 1970s, cited by the Hiroshima authorities, put the number of deaths by the end of 1945 at about 140,000 (with a margin of some 10,000). The range most commonly accepted is therefore from about 70,000 to about 140,000 deaths by the end of the year, of whom roughly half died on the first day; the great majority were civilians. The register of victims kept in the cenotaph in Hiroshima’s Peace Park, which is extended to include those who died in later decades, now holds more than 300,000 names.

Truman’s statement

Truman was returning from Potsdam aboard the cruiser Augusta when, at lunch with the crew, he was handed the report of the successful attack. The statement prepared beforehand in the War Department was released in Washington before noon on 6 August, sixteen hours after the explosion. In it the President announced that the bomb had more power than 20,000 tons of TNT and that it was an atomic bomb – “a harnessing of the basic power of the universe”. He recalled that the Potsdam ultimatum had been meant to spare the Japanese people from “utter destruction”, and warned that if Japan’s leaders did not now accept the terms, “they may expect a rain of ruin from the air, the like of which has never been seen on this earth.” American radio stations, including one on Saipan broadcasting to Japan, repeated the announcement, and leaflets urging the population to evacuate were dropped over Japanese cities.

Tokyo’s reaction

In Tokyo the first thing noticed was that the Hiroshima radio station had gone silent and telegraph links had been cut. Details came in slowly; it was from Truman’s statement that the government learned it had been an atomic bomb. An Imperial General Headquarters communiqué of 7 August said only that Hiroshima had suffered “considerable damage” in an attack by a small number of B-29s that had used a “new type of bomb”. The Army, led by its minister, Korechika Anami, tried to play down the significance of the attack until the matter had been investigated. A team led by the physicist Yoshio Nishina was sent to Hiroshima and confirmed on the spot that it had been a nuclear bomb.

The Foreign Minister, Shigenori Tōgō, concluded that the attack was a reason to accept the Potsdam Declaration quickly, and on 8 August Emperor Hirohito instructed him to seek an end to the war as soon as possible. The government, however, was still counting on Moscow’s mediation, and the military members of the Supreme Council for the Direction of the War would not agree to surrender without additional conditions. A formal meeting of the council convened only on the morning of 9 August – after the USSR had declared war on Japan.

What followed

The Americans did not wait for Tokyo’s answer. On Guam the commanders decided to bring the second attack forward because bad weather was forecast. During the night of 8–9 August the Red Army struck Manchuria, and on the morning of 9 August Major Sweeney’s B-29 dropped a plutonium bomb on Nagasaki. On 10 August Japan, through Switzerland, protested against the use of the bomb as a violation of the laws of war and at the same time offered to accept the Potsdam Declaration with a reservation concerning the prerogatives of the Emperor. On 15 August Hirohito announced the end of the war on the radio, referring in his broadcast to “a new and most cruel bomb”.

Whether, and to what extent, the atomic bombs decided the surrender remains a matter of debate among historians. In a much-discussed article of 1947 Stimson presented the decision as a choice of the lesser evil that had made it possible to avoid an invasion of the Japanese home islands and huge losses on both sides. From the 1960s Gar Alperovitz and other revisionist historians argued that Japan had been close to surrender and that the bomb was intended above all to impress the USSR. Tsuyoshi Hasegawa holds that the decisive blow was the Soviet entry into the war, whereas Sadao Asada and Richard Frank attribute the decisive role to the bombs. The dispute also concerns the casualty estimates for an invasion and whether a change in the terms regarding the Emperor might have ended the war sooner.

For Hiroshima the war did not end on 15 August. For years the survivors – the hibakusha – suffered from leukaemia, cancers and other diseases, as well as social stigma and difficulty finding work or a spouse. From 1947 their health was studied by the joint American–Japanese Atomic Bomb Casualty Commission, which was criticised for examining rather than treating them. During the occupation American censorship restricted publications about the effects of the bombing; the wider world learned of them through John Hersey’s reportage, published in 1946. Japan passed a law on medical care for the hibakusha in 1957; Koreans who survived the bombing and returned home long fought for the same entitlements.

The ruins of the Prefectural Industrial Promotion Hall, standing about 150 metres from the hypocentre, were preserved as the Hiroshima Peace Memorial, inscribed on the UNESCO World Heritage List in 1996. Every year at 8.15 a.m. on 6 August the city stops for a minute’s silence.

The attack on Hiroshima ended an era in which destroying a city required hundreds of bombers and opened the age of nuclear weapons. For some of Japan’s leaders it became an argument for ending the war quickly; it accelerated Soviet preparations for war in the Far East and the Soviet atomic programme, and four years later, when the USSR carried out its own test, it set off the nuclear arms race that dominated the Cold War. Hiroshima and Nagasaki remain the only cities on which an atomic bomb has been dropped in wartime.