⏳ End the war quickly
Every month of fighting meant more deaths among Allied troops, prisoners of war and people across Asia. American leaders hoped that a shock on this scale would bring the war to an end within days.
New Forms of Conflict: Nuclear and Guerrilla War Versus Conventional War, 1945-75 » Why the Atom Bombs Were Dropped in 1945
What you'll learn this session
Study time: 30 minutes
Edexcel spec: Paper 2 Section B, Breadth study B6, Key topic 3
- How the atom bomb was developed and why it was ready in 1945
- The five main reasons given for using atom bombs on Japan
- What the bombs did at Hiroshima and Nagasaki, in brief
- How historians weigh the reasons against each other
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This lesson is part of the Paper 2 Section B breadth study on the changing nature of warfare, 1919-2011. By the summer of 1945 the war in Europe was over, but the war against Japan was still being fought. In August the USA used a completely new weapon on two Japanese cities. It changed warfare for ever, because one bomb could now destroy a whole city. What changed: one aircraft and one bomb could now do what a huge conventional raid, such as the firebombing of Tokyo in March 1945, had done. What stayed the same: the bomb was still carried by an ordinary bomber, and the war was still fought alongside conventional forces.
Key terms:
- Atom bomb: a bomb that gets its huge power from splitting atoms. One bomb gave an explosion equal to thousands of tonnes of ordinary explosive.
- Manhattan Project: the secret American programme, helped by Britain and Canada, that built the first atom bombs from 1942.
- Unconditional surrender: giving up completely, with no deal agreed beforehand. This was the Allied demand to Japan.
- Potsdam Declaration: the warning of 26 July 1945 from the USA, Britain and China, telling Japan to surrender or face "prompt and utter destruction".
How the bomb was ready in 1945
The Manhattan Project began in 1942, partly because scientists feared that Germany might build a bomb first. It worked at secret sites such as Los Alamos in New Mexico, where the scientist J. Robert Oppenheimer led the research, and General Leslie Groves ran the project for the army. It cost about two billion dollars, a huge sum then, and employed many thousands of people.
Germany surrendered in May 1945 without a bomb. Franklin Roosevelt died in April 1945, and his successor, Harry Truman, learned of the project only after he became president. On 16 July 1945 the first bomb was tested at Trinity in the New Mexico desert, and it worked. The news reached Truman at the Potsdam Conference, where he was meeting Stalin and Churchill. Now the USA had to decide whether to use it.
Five reasons for dropping the bombs
🏝 Avoid an invasion
The USA planned an invasion of Japan, code-named Operation Downfall. The first landing, on the island of Kyushu, was set for 1 November 1945. Planners feared very heavy losses.
🚫 Japan would not surrender
Japan fought on after Germany fell and after fierce bombing of its cities, including Tokyo in March 1945. Its government did not accept the Potsdam Declaration.
💰 The cost of the project
Two billion dollars and three years of work had gone into the bomb. Some historians argue that, having spent so much, leaders found it hard to leave the weapon unused. Others say that no leader would have wasted a weapon that could save lives.
🌍 Impressing the USSR
The USSR was an ally, but relations were already tense. Some historians argue that Truman wanted to show the USSR how powerful the USA now was. The USSR had promised to join the war against Japan, and the bomb might end it before Soviet forces gained much from it.
Looking at the reasons more closely
The invasion. The fighting on Okinawa, from April to June 1945, convinced many Americans that an invasion of the Japanese mainland would be terrible. More than 12,000 Americans died there, and over 100,000 Japanese soldiers and many Okinawan civilians were killed. Japanese aircraft also made kamikaze attacks on the American fleet. Truman's advisers feared that the mainland would be defended even more fiercely. Estimates of the possible losses in an invasion varied a lot, and historians still argue about them.
Japan's refusal. The Allies demanded unconditional surrender, but some Japanese leaders wanted to keep the Emperor and the existing system of government, and some of the army leaders wanted to fight on. A few historians argue that a promise to keep the Emperor might have ended the war without the bombs. Others point out that Japan's government had not accepted the Potsdam Declaration and showed no sign of giving in.
The USSR. Historians do not agree on this reason. Some say it was a main aim, others say it was only a small extra benefit. The evidence is harder to find than for the other reasons, because it concerns private thoughts about the future rather than plans.
What the bombs did, in brief
- Hiroshima, 6 August 1945. An American B-29 bomber dropped one bomb on this port and army headquarters city. Most of the city centre was destroyed. About 140,000 people had died by the end of 1945.
- The USSR enters the war, 8-9 August. As promised, the USSR declared war on Japan on 8 August and invaded Japanese-held Manchuria the next day.
- Nagasaki, 9 August 1945. A second bomb was dropped. About 70,000 people had died by the end of the year.
- The surrender. Emperor Hirohito announced Japan's surrender by radio on 15 August 1945. Many of the injured died in the following weeks and months from burns and from radiation sickness.
Historians disagree about whether it was the bombs or the Soviet entry into the war that mattered more in persuading Japan to surrender. Either way, the war ended days after the bombs, and the world had entered the nuclear age.
Common mistakes
- Writing only "to end the war". Say how: a shock on this scale, and no need to invade.
- Saying that Germany was bombed with atom bombs. Germany had already surrendered in May 1945.
- Mixing up the dates: Hiroshima was 6 August and Nagasaki was 9 August 1945.
- Presenting one reason as a fact. Historians argue about the reasons, so write "historians argue" for the USSR and the cost.
Exam-style question
Explain TWO causes of the decision to drop atom bombs on Japan in 1945. [8 marks]
Model answer
One cause was the wish to avoid an invasion of Japan. The USA had planned Operation Downfall, with a landing on Kyushu in November 1945. The fighting on Okinawa earlier in 1945 had cost over 12,000 American lives, and American leaders feared that an invasion of the mainland would be far worse. A bomb that might force Japan to surrender without a landing therefore seemed to offer a way to save American lives, which is why Truman agreed to use it.
A second cause was Japan's refusal to surrender. After Germany fell in May 1945 Japan fought on alone, and it did not accept the Potsdam Declaration of 26 July, which had threatened it with "prompt and utter destruction". Its leaders were split over the demand for unconditional surrender, and many army leaders wanted to fight on. The USA had a working bomb, tested at Trinity on 16 July, so it chose to use it to try to end this stalemate, and dropped the first bomb on Hiroshima on 6 August.
What lifts it to the top level: two causes, each with precise facts (dates, names, figures) and a clear link showing how the cause led to the decision.
Exam tip
In a "two causes" question, give exactly two, and for each one finish with a sentence that starts "This led to the decision because...". One cause only can earn no more than half marks.
Recap
- The Manhattan Project built the bomb in secret from 1942 and it was first tested on 16 July 1945.
- Reasons: to end the war quickly, to avoid invading Japan, because Japan would not surrender, because of the cost of the project, and to impress the USSR.
- Hiroshima (6 August) and Nagasaki (9 August) were bombed, and Japan announced its surrender on 15 August 1945.
- Historians disagree about which reasons mattered most, especially the last two.