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The Atomic Bomb and why it was used on Japan

On the 6 August 1945 an atomic bomb was dropped on the Japanese city of Hiroshima. Three days later a second atomic bomb was dropped on Nagasaki. On the 15 August Japanese radio stations broadcast Emperor Hirohito’s speech announcing Japan’s surrender.

Why did Japan go to war?

During the 1930’s Japan sought to extend its influence in the Far East and create, what they would later call, the ‘Greater East Asia Co-Prosperity Sphere’. Japan, which had a shortage of natural resources, wanted to establish its own Asian Empire and become the dominant power in the region with control over its vast wealth and raw materials. In 1931 Japanese forces invaded and occupied Manchuria. In 1937 Japan launched a further invasion into China.

Japan’s expansionist policy was a threat to American, British, French and Dutch economic interests in South East Asia and led to increasing tension with Japan. In September 1940 Japan signed the Tripartite Act making them allies of Germany and Italy. In April 1941 Japan signed a neutrality pact with the Soviet Union. America gave increasing support to China in their war with Japan.

Japan had invaded and occupied the north of French Indochina in September 1940, mainly to prevent supplies reaching the Chinese armies. In July 1941 Japanese forces invaded further to the south. America and Britain imposed an embargo on all oil exports to Japan. With limited natural resources, Japan was heavily dependent on imports of oil. The Imperial Japanese Navy, it was warned, would run out of fuel for its ships within a year.

On Sunday 7 December 1941 Japan launched an attack on the U.S. naval base at Pearl Harbor, Hawaii without any warning. It was a pre-emptive strike intended to cripple the U.S. Pacific Fleet and with it America’s ability to stop Japan’s plans for the conquest of South East Asia.   America declared war on Japan the following day.

Conquest

Within hours of the bombing of Pearl Harbor Japanese forces launched attacks against the Philippines, Wake Island, Guam and the British territories of Malaya and Hong Kong.  Malaya had extensive rubber plantations but its invasion was also part of a wider strategy to capture Singapore, an important British naval base.  On 15 February 1942 after seven days of fighting, Lieutenant General Arthur Percival surrendered Singapore to the Japanese. Winston Churchill called the fall of Singapore “the worst disaster and largest capitulation in British history.”

The Japanese made further advances, capturing the oil rich Dutch East Indies (Indonesia) and forcing the Allied troops in Burma to retreat to India. Vast swathes of South East Asia were under Imperial control. Japanese occupation was brutal and oppressive. Thousands of civilians and prisoners of war were used as forced labour and many atrocities were carried out against them by the Japanese.

The Allies strike back

The U.S. Navy inflicted severe losses on the Japanese fleet at the Battle of Midway in June 1942. Admiral Yamamoto had planned to ambush the U.S. Pacific Fleet, primarily to destroy their aircraft carriers which had been at sea during the attack on Pearl Harbor. However, American codebreakers knew there was going to be an attack on Midway and a fleet of American warships assembled there, surprising the Japanese.

The Allies began a tactic of ‘island hopping’, a strategy which involved removing Japanese forces from the Pacific islands one by one. The first of these, Guadalcanal in the Solomon Islands was recaptured in early 1943.

In March 1945 after 36 days of fierce fighting U.S. forces recaptured Iwo Jima. At the beginning of April 1945 U.S. troops landed on Okinawa. They encountered strong Japanese resistance and incurred severe casualties in one of the bloodiest campaigns of the Pacific War. By the time the Japanese forces surrendered in late June, almost 10,000 American sailors had been killed or wounded, most victims of Japanese Kamikaze pilots. There were thousands of civilian casualties and Japanese dead were estimated at around 100,000 men.

By the middle of 1945 the Japanese army had suffered several defeats throughout the Pacific and there were frequent bombing raids of the Japanese mainland. After a long, hard fought campaign in Burma, Allied forces captured Rangoon at the beginning of May 1945, although fighting continued until August.

The development of the atomic bomb

In 1938 the German physicists Otto Hahn and Fritz Strassmann demonstrated uranium fission, or splitting of the atom. This meant that an atomic weapon was theoretical possible.

In August 1939 Albert Einstein sent a letter, written by physicist Leó Szilárd, to the American President, Franklin D. Roosevelt. He warned that Germany might be in the process of developing an atomic bomb and that America should secure supplies of uranium ore and start its own nuclear research project. This led to the development of the Manhattan Project. The project accelerated in 1942 after America entered the war against Japan and Germany. Brigadier General Leslie R. Groves of the U.S. Army Corps of Engineers was made head of the project.

In Britain the Maud Committee had looked into the development of an atomic bomb. In 1941 Britain had its own atomic weapons program known as Tube Alloys. President Roosevelt and Prime Minister Winston Churchill agreed that Britain and America would work together to try and create an atomic weapon before Germany. They also agreed that this research would be kept secret, particularly from Stalin and the Soviet Union. The Soviets had their own atomic weapons project. They also had spies within the Manhattan Project.

Construction companies built huge factories. Thousands of engineers and scientists, including several Nobel Prize winners, worked at sites across America. All work was top secret. Most people involved with the Manhattan Project did not know what they were actually working on. The United States spent $2 billion on the project and, at its peak, had over 125,000 people working on it.

Two types of atomic bomb were developed, a gun-type uranium bomb and an implosion-type plutonium bomb. Plutonium had only recently been discovered and there was very little available in the world. Huge reactors were built in Hanford, Washington State to synthesise enough to make a bomb.  Enriched Uranium 235 was produced at a purpose built facility in Oak Ridge, Tennessee.  

In 1943 Los Alamos, New Mexico was chosen as the site for the laboratory that would design and build the bomb. General Groves appointed the physicist J. Robert Oppenheimer as its scientific director. A small town was hastily constructed to house all the scientists. By 1944 about 6000 people were living at Los Alamos.

On the 16 July 1945 at 5.30am in the desert near Alamogordo the first plutonium bomb, ‘the gadget’, was detonated. After the success of the Trinity test Oppenheimer quoted the Bhagavad Gita, “Now I am become Death, the destroyer of worlds”.

The decision to use the bomb

Germany had surrendered to the Allies on the 8 May 1945, but work continued on developing the atomic bomb. The Military Policy Committee in Washington had already regarded Japan as a target for an atomic bomb as early as May 1943.  President Harry Truman (Roosevelt had died in April 1945) reiterated in his VE Day speech that the war against Japan would only end with their unconditional surrender.

The Interim Committee was set up at the beginning of May 1945 to oversee the development of the atomic bomb and its use. On the 1 June the Interim Committee recommended that “…the bomb should be used against Japan as soon as possible; that it be used on a war plant surrounded by workers’ homes; and that it be used without prior warning…”

Japan’s navy and air force were crippled as a fighting force. The naval blockade had cut off supplies of raw materials vital to the Japanese war effort, reducing manufacturing output. There were also food shortages. The Japanese mainland was subjected to frequent bombing raids. This included a firebombing campaign using an early form of napalm. On the night of the 9-10 March 1945 incendiary bombs were dropped on Tokyo. The resulting fires tore through the wooden and paper houses leaving over 100,000 people dead or wounded. Despite this the Japanese showed no sign of surrendering.

President Truman had the option to continue with the naval blockade and the bombing raids. Plans were also being drawn up for an invasion of the Japanese mainland. Codenamed Operation Downfall, it was scheduled to begin on the 1 November. The Japanese realised that an American invasion was likely and had already been improving their defences and preparing their armed forces and civilian population to defend the Japanese homeland. The fierce fighting at Iwo Jima and Okinawa clearly demonstrated what resistance could be expected. President Truman did not favour the land invasion as it would lead to thousands of casualties. Many in America felt that the war should be brought to an end as quickly as possible to save the lives of U.S. servicemen.

There was great hostility in America towards the Japanese after the attack on Pearl Harbor and over their brutal treatment of prisoners of war. After U.S. forces surrendered to the Japanese in the Philippines on 9 April 1942, over 7000 American and Filipino prisoners died on their way to the prison camp during the ‘Bataan death march’. 

Some of the Manhattan Project scientists, including Leó Szilárd, objected to the dropping of the bomb on Japan. It was suggested that instead there could be a technical demonstration of the bomb’s capabilities. The report of the Scientific Panel to the Interim Committee stated that “…they saw no acceptable alternative to direct military use…”

President Truman was attending the Potsdam Conference when he heard of the successful atomic weapons test. On 26 July the United States, Great Britain and China issued the Potsdam Declaration which demanded “…the unconditional surrender of all the Japanese armed forces…The alternative for Japan is prompt and utter destruction.” The Declaration made no mention of the atomic bomb.

The Japanese government was divided. The military leaders wanted to continue fighting, in part because it was seen as dishonourable to surrender but also in the belief they could force better terms in the face of rising Allied casualties. Others within the government were seeking a way to end the war and had been trying to get the Soviet Union to act as mediators in peace negotiations. Japan would not surrender unconditionally. Chief among their conditions were that the Imperial House and Emperor Hirohito remain in place. Japan rejected the Potsdam Declaration.

President Truman had already authorised the use of the atomic bomb, “…release when ready but not sooner than August 2”.

Hiroshima 6 August 1945

Hiroshima held the headquarters of the Japanese Second Army and the Chugoko Regional army. It did have industrial units but these were mainly located on the outskirts of the city. Hiroshima was also selected as a target because it had not been subjected to heavy bombing. Most of the city’s structures and buildings were still intact. This would better demonstrate the power of the new bomb and inflict the greatest psychological impact on the Japanese.

On the 6 August the B-29 bomber the Enola Gay, named after the mother of its pilot Colonel Paul Tibbets, left Tinian carrying the uranium bomb, Little Boy.

At 8.15am the atomic bomb detonated 1900ft (580m) above the city of Hiroshima. There was a brilliant flash of light, it only lasted for a few moments but the intense heat caused people up to 2km away to suffer flash burns on exposed skin. Those in the immediate vicinity were left charred and blackened. The blast wave demolished buildings, many injuries were caused by flying debris and collapsing structures. The fires that had started turned into a firestorm, killing people trapped in the rubble. The city of Hiroshima was built on flat terrain and the blast and resulting fires devastated over 4 square miles of the city. It is estimated that 70-80,000 people were killed with a similar number injured.Peace Memorial Park

There had been no warning of the coming attack. The bomb detonated 45 minutes after the all clear had sounded from a previous alert. Most people were at or on their way to work. Many school children were out in the open on demolition parties making firebreaks between the buildings.

Those emergency services that had not been destroyed by the blast were overwhelmed by the scale of the disaster. Relief centres were set up but there were few medical supplies or trained medical personnel available to help the thousands who had been injured.

People left the city in long lines of walking wounded. Hundreds arrived in the city to find relatives and help with the relief effort, unknowingly exposing themselves to the radiation. Within a week of the atomic blast people began to suffer and die from radiation sickness.

President Truman issued a statement after the dropping of the bomb on Hiroshima “…If they do not now accept our terms they may expect a rain of ruin from the air, the like of which has never been seen on this earth…”

The Japanese government were still divided over how to end the war. The military leaders were prepared to fight to defend the Japanese homeland and viewed the destruction of Hiroshima as no different from the cities destroyed by firebombing. They also doubted that there were many of these new weapons available.  The government continued to debate their course of action and their conditions for surrender.

Nagasaki 9 August 1945

With no official response from Japan the next atomic bomb was made ready. The date for the attack was moved forward from the 11 August to the 9 August to avoid a period of incoming bad weather.

The B-29 bomber Bockscar left Tinian early on the morning of the 9 August carrying the plutonium bomb, Fat Man. The initial target was Kokura but it was obscured by cloud so Bockscar moved on to its secondary target, Nagasaki.

The atomic bomb detonated at 11.02am 1650ft (500m) above Nagasaki, with a force equivalent to 22,000 tons of TNT, more powerful than the uranium bomb that had been dropped on Hiroshima.

The bomb detonated over the Urakami Valley which confined the shockwave. Although fires were started by the blast, this time there was no firestorm. The Nagasaki Prefectural Report stated that “…within a radius of 1km from ground zero men and animals died almost instantaneously from the tremendous blast pressure and heat…”  It is estimated that over 35 000 people were killed with a greater number injured.

>As at Hiroshima, the remaining emergency services struggled to cope with the scale of the disaster. There were mass cremations and burials in the days after the attack in order to control the spread of disease.

Surrender

The Soviet Union declared war on Japan, violating the neutrality pact. On August 9, over 1.5 million Soviet troops invaded Japanese held territory in Manchuria along a 4400km front.

The Japanese government continued to disagree over what course of action to take. The Emperor informed them that they should surrender with the proviso that he kept his position as Imperial Ruler. On August 10 Japan formally announced that they would accept the terms of the Potsdam Declaration only on the condition that it did not comprise any demand which prejudices the prerogatives of His Majesty as a Sovereign ruler.”

Bombing raids continued to be carried out on the Japanese mainland. Atomic bomb production also continued, although President Truman had issued an order that they could only be released with his “express authority”. Japan finally agreed to accept the terms of surrender.

Emperor Hirohito’s capitulation announcement was broadcast to the people of Japan on the 15 August. There was no mention of surrendering. The Emperor informed the nation that “…the war situation has developed not necessarily to Japan’s advantage…” the Emperor also made reference to the “…new and most cruel bomb…” and that to continue the war would lead to the “…obliteration of the Japanese nation…the total extinction of human civilization…”

On the 17 August the Emperor’s speech to the Japanese armed forces explained that they could not continue fighting now that the Soviet Union had entered the war. No mention was made of the atomic bomb.

Japan formally surrendered on the 2 September 1945 on the deck of the USS Missouri.

Aftermath

The initial response to the use of the atomic bombs was that they had shortened the war and consequently saved the lives of Allied servicemen. There was also a sense of retribution, particularly in America, for the atrocities carried out by the Japanese against prisoners of war and the attack on Pearl Harbor. There were some voices of discontent on the use of the atomic bombs against civilians.

Peace Memorial Park

As evidence emerged of the human cost of the bomb, particularly the ongoing effects of the radiation, more moral and ethical objections were raised over its use. The advent of the Cold War and the nuclear arms race also negatively impacted people’s perceptions of atomic weapons.

In the years since there has been much debate over whether the atomic bombs should have been used on Japan, whether they did actually hasten the end of the war, and if America’s deteriorating relationship with the Soviet Union influenced the decision to use them.

In Japan the survivors of Hiroshima and Nagasaki, known as hibakusha or ‘explosion-affected people’, suffered from discrimination, mainly out of fear of the effects of the radiation. Many suffered and still suffer from health problems. The hibakusha have mounted several legal challenges against the Japanese government to get their medical conditions recognised as being linked to their exposure to the atomic bombs.

* Images of Peace Memorial Park, Hiroshima provided by Michael Hill