Every other episode in this series has ended with something to hold onto. Somebody was brave, or clever, or kind, or all three.
This one does not work like that, and it would be dishonest to pretend otherwise.
What happened at the end of the war in the Pacific is the single most argued-about event of the twentieth century, and people who have spent their whole lives studying it disagree completely and in good faith.
So this episode is not going to tell you what to think. It is going to tell you what happened and what the argument actually is, and then it is going to leave it with you, which is a slightly unusual thing to do at bedtime and is the right thing to do here.
By the summer of nineteen forty five, Japan had lost the war by any military measure and had not surrendered.
Its navy was largely gone. Its cities were being bombed almost without opposition. Its merchant fleet had been destroyed by submarines, which for an island that imports its food and fuel is decisive on its own.
The fighting on the islands had been getting worse rather than better. On Okinawa, between April and June, something over twelve thousand American servicemen were killed, and Japanese military deaths ran to well over seventy thousand, and the civilian death toll on that one island is usually estimated between a hundred and a hundred and fifty thousand people.
There is one more thing that belongs here and is often left out. The heaviest single air raid of the entire war was not an atomic one. On the night of the ninth of March, nineteen forty five, Tokyo was firebombed, and something approaching a hundred thousand people died in one night, and around a million were left homeless.
That happened five months before August, and by the summer around sixty Japanese cities had been attacked in the same way.
The plan for finishing the war conventionally was called Operation Downfall, and it was to be an invasion of the Japanese home islands in two stages, beginning in November nineteen forty five.
It would have been considerably larger than D-Day.
The casualty estimates made at the time varied enormously, which is itself important. Different staffs produced different numbers using different assumptions, ranging from tens of thousands of American dead up to several hundred thousand, and Japanese casualties, military and civilian, would have been very much higher again.
The figures later quoted in public were at the top of that range, and historians argue about whether they were honest estimates or numbers chosen afterwards to justify a decision. Both things may be true of different documents.
What is not seriously disputed is that the Japanese government had ordered preparations for civilian resistance, that Okinawa had shown what that looked like, and that everybody planning Downfall expected it to be appalling.
For three years, in laboratories and factories across the United States, over a hundred thousand people had been working on a project most of them could not describe. It was called the Manhattan Project, and the first device was tested in the New Mexico desert on the sixteenth of July, nineteen forty five.
On the sixth of August, an atomic bomb was dropped on Hiroshima. On the ninth of August, a second was dropped on Nagasaki.
The number of people killed is not precisely knowable and the estimates vary. The most commonly cited figures are around seventy to eighty thousand people killed at Hiroshima on the day, and around forty thousand at Nagasaki, with the totals by the end of that year roughly doubling as people died of injuries and of radiation, which was an effect the scientists understood only partly and the world did not understand at all.
This series has made a rule of not describing suffering in detail, and it is going to keep that rule here, where it matters most.
On the eighth of August, between the two bombs, the Soviet Union declared war on Japan and invaded Manchuria with a very large army. Japan had been hoping, up to that point, to use the Soviet Union as a neutral go-between to negotiate. That hope ended overnight.
On the fifteenth of August, the Emperor's voice was broadcast to the Japanese people, most of whom had never heard it, announcing that the war would end. The formal surrender was signed on the second of September.
Here is the argument, as fairly as it can be put in a few paragraphs.
One side holds that the bombs ended the war and that the alternative was an invasion that would have killed far more people, Japanese people above all, and that the firebombing which was already destroying Japanese cities month after month would have continued for another year. On this reading it was a terrible act that prevented a worse one.
The other side holds several things at once. It holds that Japan was already defeated and blockaded and would have surrendered within months. It holds that the Soviet declaration of war on the eighth of August was at least as decisive as the bombs, and possibly more so, and that the timing of the Japanese decision supports this. It holds that the terms could have been clarified earlier, particularly regarding the Emperor, which was the sticking point and was in the end conceded anyway. And it holds that a demonstration on an unpopulated target was never seriously tried.
There is also a reading that says the second bomb, three days later, was harder to justify than the first, whatever you think of the first.
And there is a further argument that the decision was shaped partly by the Soviet Union, and by a wish to end the war before Soviet forces were in a position to claim a share of the settlement in Asia.
Historians have been over the documents for eighty years. They have not settled it. That is not because they are careless. It is because the question requires you to compare things that cannot be compared, and to guess at what would have happened in a world that did not happen.
There is one story from Hiroshima that is usually the way children first meet this, and it is a good way, so it belongs here.
Sadako Sasaki was two years old and about a mile from the centre of the city when the bomb fell, and she was not hurt. She grew up healthy and fast, and was the best runner in her class.
When she was eleven she became ill with leukaemia, which was appearing among survivors in numbers that had no other explanation.
In hospital she was told about an old Japanese tradition that a person who folds a thousand paper cranes is granted a wish. She began folding. She used medicine wrappers and any paper she could get, and she folded very small ones, some no bigger than a fingernail, using a needle.
Accounts differ on how many she completed, and the version told in Japan is that she folded well past a thousand and kept going. She died in nineteen fifty five, aged twelve.
Her classmates raised money for a monument, and there is now a statue of her in Hiroshima holding a crane above her head, and at the base of it an inscription that says: this is our cry, this is our prayer, peace in the world.
People send folded paper cranes there from all over the world. They arrive by the tonne every year, in strings of a thousand, mostly made by children.
Nobody has used a nuclear weapon in war since the ninth of August, nineteen forty five. That is nearly eighty years, through a great many crises, several of which came far closer than the public knew at the time. It is the most important fact in this episode.
Many of the scientists who built it spent the rest of their lives arguing about it. A petition signed by dozens of them asked that it not be used on a city without a warning and a chance to surrender. It did not reach the President before the decision. Several of them devoted their later careers to arms control.
The people who were there rarely speak in the terms the argument uses. Survivors of Hiroshima, called hibakusha in Japanese, have mostly campaigned for one thing, which is that it should not happen again to anybody, and a number of them have said explicitly that they are not interested in assigning blame because it does not help.
Here is something to think about tonight, and it is a genuinely open question rather than a puzzle with an answer. Some decisions are made between two bad choices, where every option costs lives, and where nobody will ever know for certain what the other path would have cost. How should we judge people who had to make one of those?