The decision to drop the atomic bombs

What the specification asks for

“Reasons for dropping atom bombs in 1945.” — examined through causation. Incandio is aligned to specification 4HI1; it is not published by, endorsed by or affiliated with Pearson.

1 · Understand it

Where the war stood in July 1945

Germany had surrendered in May. Japan had lost its fleet, its merchant marine and most of its air force; American bombers were burning Japanese cities with incendiaries, and the firebombing of Tokyo in March 1945 had killed a number usually estimated at around 100,000 people in a single night. Japan had not surrendered.

The American government was planning an invasion of the Japanese home islands for late 1945 and 1946. Casualty estimates prepared at the time varied enormously, and the very high figures quoted afterwards were not the figures in front of the decision-makers; the honest statement is that a costly campaign was expected and that nobody knew how costly.

The Trinity test on 16 July 1945 showed that the weapon worked. Hiroshima was attacked on 6 August and Nagasaki on 9 August. The Soviet Union declared war on Japan on 8 August and invaded Manchuria — which places a second enormous shock between the two bombs.

The reasons that are argued about

The first reason offered at the time and since is military: to end the war without an invasion, and therefore to save the lives that an invasion would have cost on both sides. This is the argument of the men who took the decision and it is not to be dismissed.

The second is diplomatic. The bomb was ready at the moment the Soviet Union was about to enter the Pacific war and to acquire a claim on the settlement in Asia. Some historians argue that ending the war quickly, and demonstrating the weapon, was intended to limit Soviet gains and to shape the post-war relationship. Others reply that the documents show the weapon being treated as a means of ending the war, and that its diplomatic value was a bonus rather than a motive.

The third is institutional momentum. Two billion dollars and three years of work had produced a weapon; the assumption from the beginning of the project had been that it would be used; and the question of whether to use it at all was never put in the form later generations assume.

The fourth concerns the Soviet declaration of war on 8 August. Some scholarship on the Japanese side argues that the Supreme Council was moved more by the collapse of the hope of Soviet mediation than by Hiroshima, and that the second bomb and the invasion of Manchuria arrived together in the deliberations. This does not tell us why the Americans dropped it; it tells us what ended the war, which is a different question.

How to argue this without arguing about morality

The examination question is causal, not ethical: what were the reasons, and how far does each explain the decision. A candidate who spends an answer on whether it was right has answered a question that is not on the paper.

The strongest structure separates the American decision from the Japanese surrender. The reasons for dropping are about Washington in July 1945; the causes of surrender are about Tokyo in August 1945, and the evidence for the two is different. An answer that keeps them apart can weigh the Soviet declaration properly instead of using it as a knock-down on both counts.

2 · Learn it — the notes

The dates that earn marks

16 July 1945

The Trinity test in New Mexico. Why this date: It is the first moment at which the weapon was a fact rather than a hope, and it falls during the Potsdam Conference.

6 August 1945

Hiroshima. Why this date: The first use, and the point from which every argument about deterrence in the rest of this option runs.

8 August 1945

The Soviet Union declares war on Japan and invades Manchuria. Why this date: It falls between the two bombs, which is why the causes of the Japanese surrender cannot be settled by naming Hiroshima alone.

9 August 1945

Nagasaki. Why this date: The second use, three days later, is what makes the question of why twice examinable.

15 August 1945

The Japanese surrender is announced. Why this date: It dates the outcome the decision was meant to produce, six days after the second bomb.

The figures, and how far to trust them

• Around 100,000 — Deaths in the firebombing of Tokyo, 9–10 March 1945. (Estimates vary widely and no count was possible at the time. It is quoted here because it establishes that mass civilian death by air attack preceded the atomic bombs.)
• Tens of thousands immediately; substantially more by the end of 1945 — Deaths at Hiroshima. (Immediate and end-of-year totals differ enormously because of radiation deaths, and published estimates range widely. A bare single number misrepresents the record.)
• 16 July 1945 — The Trinity test date, which falls inside the Potsdam Conference.

The people to place

• Harry Truman — President of the United States; took the decision to use the weapons.
• J. Robert Oppenheimer — Scientific director of the Los Alamos laboratory, where the weapons were designed.

How historians disagree

Attributed interpretations, never voiced — the AO4 seam.

• The military-necessity reading: The bombs were used to end the war without an invasion of the home islands, and the alternative was a campaign of unknown but very large cost. Contested by The reading associated with Gar Alperovitz, which holds that the timing and the diplomacy around Potsdam show the weapon being used with an eye to the Soviet Union and the shape of the post-war world..
• The 'Soviet entry ended the war' reading: Japanese records show the Supreme Council moved decisively after the Soviet declaration of 8 August, which destroyed the hope of a mediated peace, rather than after Hiroshima alone. Contested by The reading that the two shocks were inseparable in the deliberations, and that separating them imposes a tidiness the record does not have..

What students say — and what is actually the case

Not this: The atomic bombs were the first time large numbers of Japanese civilians were killed from the air.

This: The firebombing campaign from March 1945 had already destroyed large parts of many cities, with a single night in Tokyo killing a number usually estimated at around 100,000.

Not this: Japan surrendered because of Hiroshima.

This: The Soviet declaration of war fell between the two bombs and removed Japan's hope of a negotiated peace through Moscow. Historians disagree about the weight of each, and the disagreement is the examinable point.

Two things students merge

Blurred: The reasons for dropping the bomb and the causes of the Japanese surrender.

The distinction: The first is a question about American decision-making in July 1945; the second is about Japanese decision-making in August. They use different evidence and can have different answers, and merging them is the commonest structural error on this strand.

Blurred: A demonstration and a use.

The distinction: Some scientists proposed a demonstration on an uninhabited target. The decision taken was a use against a city, which is what makes the diplomatic argument possible: a demonstration would have signalled capability without the same effect.

What a Grade 9 answer holds here

A Grade 9 answer refuses to let the two questions collapse into each other. Whether Washington used the bomb to end the war or to impress Moscow is settled by American evidence; whether Tokyo surrendered because of the bomb or because of the Soviet declaration is settled by Japanese evidence — and it is entirely coherent to answer military necessity to the first and the Soviet entry to the second.

3 · How it is examined

This strand is genuinely set through: Paper 2 Section B (a) (6 marks — “Explain TWO ways in which … was different from ….”); Paper 2 Section B (b) (8 marks — “Explain TWO causes of ….”); Paper 2 Section B (c)(i) or (c)(ii) (16 marks — “How significant was … in …, in the years …? / How far were … responsible for …, in the years …? You may use the following in your answer: • [prompt] • [prompt]. You must also use information of your own.”).

What earns marks: The date of the Soviet declaration, 8 August, placed correctly between the two bombs. It is the single fact that lets a candidate weigh causes instead of asserting one.

The cap that bites here: The 8-mark cause question caps a single cause at 4 marks. Two developed reasons, not one brilliant one.

4 · Prove it — the questions

Answered inside Incandio, where a marker checks what a correct answer must contain and tells you which half was missing. The marking stays in the app; the questions are here.

1. Explain TWO ways in which the bombing of Hiroshima was different from the bombing of Tokyo in March 1945. [6 marks · Paper 2 Section B (a)]
2. Explain TWO causes of the American decision to use atomic weapons against Japan in 1945. [8 marks · Paper 2 Section B (b)]
3. Explain TWO causes of the Japanese surrender in August 1945. [8 marks · Paper 2 Section B (b)]
4. How significant was the atomic bomb in changing the nature of warfare, in the years 1945–2011? [16 marks · Paper 2 Section B (c)(i) or (c)(ii)]
5. How far were diplomatic considerations responsible for the decision to drop the atomic bombs in 1945? [16 marks · Paper 2 Section B (c)(i) or (c)(ii)]

Carry on through the option

• Previous lesson, in key topic 2: U-boats, amphibious operations and aircraft carriers
• Next lesson: The arms race, MAD and proliferation
• Also in this key topic: Conventional and guerrilla war, 1945–75
• Key topic 3 · New forms of conflict – nuclear and guerrilla war versus conventional war, 1945–75 · The changing nature of warfare and international conflict, 1919–2011 · the option's timeline · Incandio History
• The other key topics of The changing nature of warfare and international conflict: The changing nature of warfare, 1919–39 · Changing methods of warfare by land, air and sea, 1939–45 · Conventional war and the development of 'new' wars, 1976–2000 · Changing methods of warfare at the beginning of the 21st century, 2000–2011