August 6 marks the 75th anniversary of the dropping of the first nuclear bomb that ended the Second World War in the Pacific.

Debate still rages about why the United States dropped two nuclear bombs on the Japanese cities of Hiroshima and Nagasaki on 6 and 9 August 1945, killing hundreds of thousands of civilians and unleashing the most powerful and devastating weapon on the world. Was it a necessity to end the Second World War quickly to save more lives, or was it designed to halt the advancement of Soviet forces in Asia, thereby kick-starting the Cold War?

After the defeat of Germany in May 1945, the war in the Pacific continued, despite the tide being turned against Japan. With the end of the Second World War in Europe, the whole force of the United States was against Japan and there was also the prospect of the Soviet Union entering the Pacific War. Furthermore, the British had just launched a major offensive against Japanese armies in Southeast Asia.

However, Japan continued to maintain its position in China, ruining American hopes of using that country as a launch pad for an attack on Japan. There were still a large number of Japanese planes available for Kamikaze attacks against American ships, and the Japanese were determine not to give in to the American insistence of an unconditional surrender.

Not even the entrance of American long range B29 bombers and the major damage they had done on Japan, crippling much of its industrial capacity and killing tens of thousands of civilians, convinced Japan to sue for peace.

But the United States had another devastating card to play: the atomic bomb.
Its development was a demonstration of the strength of American capabilities in the Second World War. The United States easily afforded to spend about $2 billion to develop just three atomic bombs by 1945. So secret were the plans to develop the nuclear bombs that even the American Vice-President, Harry Truman, did not know if their existence.

Truman learned about the Manhattan Project – the name of the construction process for the atomic bombs – after the death of Roosevelt in April 1945.

He then learned about the successful test of one of those bombs in the New Mexico desert on 16 July 1945 while he was attending the Potsdam conference with Stalin and Churchill.

For Truman, these bombs could potentially solve a problem about ending the war.
A common argument given for why Truman decided to drop the two bombs is that it would solve the dilemma of an invasion of Japan. The United States invasion of the Japanese island of Okinawa in April 1945 that resulted in up to 160,000 Allied and Japanese casualties, demonstrated the huge likely cost in American lives and money of an invasion of Japan.
At Potsdam – one of the allied meetings between the United States, United Kingdom and the Soviet Union – the allies called on Japan to surrender. After Japan rejected that call, Truman made up his mind to use the atomic bomb.

This new weapon could potentially avoid an invasion of Japan.

However, there is another argument as to why Truman wanted to use the bomb.

He was much less happy than Roosevelt about the prospect of the Soviet Union entering the Pacific War.
Roosevelt had sought to secure Soviet entry into the war against Japan once Germany was defeated. At the Yalta conference of the allied heads of state in February 1945, Roosevelt had agreed to a number of concessions requested by Stalin in return for Soviet troops entering the Pacific War. In particular, the Soviet Union would be given the right to least Port Arthur in the northern Chinese region of Manchuria as a naval base, the internationalisation of the major Manchurian port of Darien, and joint Soviet-Chinese ownership of the South Manchuria and Chinese eastern railways. These concessions would give the Soviets a foothold in the economically rich province.

Truman believed there was evidence that Stalin was already breaking terms of the Yalta agreement in Eastern Europe. He also suspected that the Soviet Union would try to increase its presence in Asia on top of the concessions granted to Stalin at the Yalta conference. The atomic bomb presented the prospect of convincing Japan to sue for peace before the Soviet Union was ready to declare war on Japan.
The Soviets entered the war on 9 August 1945, the day the second bomb was dropped on Nagasaki and six days before the Japanese Emperor publically surrendered on 15 August 1945. The intervention in the war by Stalin was of no military value as Japan’s fate had already been sealed with the dropping of the first atomic bomb on Hiroshima on 6 August 1945.

While the two atomic bombs certainly did bring an earlier end to the war, the dropping of the bombs did not prevent Soviet entry into the Pacific War – a last minute intervention that allowed the Soviet Union to occupy the northern half of Korea and install a communist regime there.

This article was written by National Security College Senior Lecturer, Dr Sue Thompson.