11.10 — The Bomb

At 8.15 a.m. on 6 August 1945, a uranium bomb detonated about 580 metres above Hiroshima.

The people directly beneath were vaporised. Some left shadows on stone — the radiation bleached the surrounding surface and the body shielded a patch. One such shadow, on the steps of a bank, is preserved.

Estimates of deaths by the end of 1945: around 90,000 to 146,000 at Hiroshima and 60,000 to 80,000 at Nagasaki, from blast, fire and acute radiation sickness, with cancers appearing for decades afterwards.

This chapter covers how it was built, what the decision actually involved, and the argument about it — which is not settled and which this book will not pretend is.

The physics, briefly

Volume IV covers it properly. Here is what is needed.

Certain heavy nuclei — uranium-235 and plutonium-239 — split when struck by a neutron, releasing energy and two or three more neutrons.

If enough fissile material is packed densely enough, each fission triggers more than one further fission on average, and the number of fissions doubles repeatedly in microseconds. That is a chain reaction, and the amount needed is the critical mass.

The engineering problem was separation. Natural uranium is over 99 percent uranium-238, which does not sustain a chain reaction, and about 0.7 percent uranium-235, which does. The two are chemically identical and differ in mass by about one percent, so separation required enormous industrial plants using gaseous diffusion and electromagnetic methods.

Plutonium does not occur in nature and had to be manufactured in reactors.

The two bomb designs differed accordingly. The uranium bomb used a gun assembly — firing one piece of uranium into another — which was considered so reliable it was never tested. The plutonium bomb required implosion — a precisely shaped shell of conventional explosive compressing a sphere symmetrically — which was difficult enough to require the Trinity test on 16 July 1945.

The Manhattan Project

It began because of a letter. In August 1939, Leo Szilard drafted and Albert Einstein signed a letter to Roosevelt warning that extremely powerful bombs might be constructed and that Germany had stopped the sale of uranium from occupied Czechoslovakia.

The fear of a German bomb is the founding motive, and a very large proportion of the scientists involved were refugees from Nazi Europe.

The scale. Around 130,000 people employed, at a cost of about two billion dollars in 1940s money. Entire secret cities were built — Oak Ridge in Tennessee, Hanford in Washington, Los Alamos in New Mexico. Most of the workforce did not know what they were making.

And the German bomb did not exist. The German programme, under Heisenberg, was far behind — under-resourced, and mistaken about the critical mass and the moderator required. The Allies did not know this until late in the war.

Germany surrendered in May 1945, before the first test.

Which produced the first moral crisis. The Franck Report, submitted in June 1945 by scientists at Chicago, argued against a surprise attack on a city and proposed a demonstration before neutral observers. A petition organised by Szilard was signed by around seventy scientists. Neither reached the President before the decision.

Joseph Rotblat left the project in late 1944 when it became clear Germany was not building a bomb — the only scientist to do so on those grounds. He spent the rest of his life on nuclear disarmament and received the Nobel Peace Prize in 1995.

The decision

The arguments made at the time and since, stated fairly on both sides, because this is one of the genuinely contested questions in modern history.

The case that it was necessary

Japan had not surrendered despite hopeless circumstances (Chapter 11.8). Its cities were burning; its navy and merchant fleet were destroyed; and the government remained divided with the army faction insisting on continuing.

Invasion was the alternative and its projected cost was enormous. Operation Downfall was planned for November 1945. Estimates of American casualties varied widely — contemporary military estimates ranged from tens of thousands to several hundred thousand — and Japanese military and civilian casualties would have been far higher. Okinawa, where perhaps a third of the civilian population died, was the model everyone had in mind.

The blockade alternative would have starved Japan. Japan was already facing famine conditions in 1945, and a siege lasting into 1946 would have killed very large numbers of civilians.

And the Japanese army attempted a coup after the Emperor decided to surrender, seizing the palace on the night of 14–15 August to prevent the broadcast. It failed narrowly. That is evidence of how hard surrender was to achieve.

The case that it was not

Japan was already seeking terms through Soviet mediation, which American codebreakers had intercepted. The sticking point was the position of the Emperor — and the United States ultimately permitted the Emperor to remain, which is the assurance Japan had sought. Giving it earlier might have produced surrender without the bombs.

The Soviet declaration of war on 8 August, and its rapid destruction of the Japanese army in Manchuria, may have been the decisive shock. The historian Tsuyoshi Hasegawa's work argues from Japanese sources that the Soviet entry weighed more heavily in the Supreme Council's deliberations than the bombs, because it removed the last hope of a mediated peace.

Several senior American commanders expressed retrospective doubt — Eisenhower, Leahy and others wrote afterwards that they had believed it unnecessary. Retrospective statements are weaker evidence than contemporary ones and they are on the record.

And Nagasaki is harder to defend than Hiroshima. Three days is not long for a shattered government with destroyed communications to assess and decide.

The Soviet dimension. That the bombs were used partly to demonstrate American power to the Soviet Union — the argument advanced by Gar Alperovitz — is contested. The documentary evidence for it as a primary motive is thin; the evidence that it was among the considerations is stronger.

What can actually be said

The decision was made in a context where mass killing of civilians by bombing had already been normalised (Chapter 11.7 and 11.8). The firebombing of Tokyo had killed more people than either bomb. The atomic bombs were not a moral departure in intent; they were a change in efficiency.

And they were not perceived at the time as categorically different by most decision-makers, which is the most disturbing fact in the chapter.

This book's position: the question of whether it was necessary is genuinely open and the evidence supports neither confident verdict. What is not open is what the weapons do, which is the subject of the next section.

What happened

Blast. A pressure wave that flattened buildings for kilometres.

Heat. Temperatures at the point of detonation of millions of degrees; thermal radiation that caused fatal burns kilometres away and ignited everything flammable, producing a firestorm at Hiroshima.

Prompt radiation, which caused acute radiation sickness in people who survived the blast — nausea, then an apparent recovery, then bleeding, hair loss, infection and death over days or weeks.

And long-term effects. Elevated rates of leukaemia from a few years afterwards, and of solid cancers for decades. The survivors — hibakusha — faced social discrimination in Japan, including in marriage, because of fears about heredity.

The Hiroshima Peace Memorial — the one building left standing near the hypocentre, preserved as a ruin — and Sadako Sasaki's paper cranes, folded by a girl who died of leukaemia at twelve, are the two images the event is remembered by.

What followed

The Soviet Union tested in 1949, assisted by extensive espionage including by Klaus Fuchs, a physicist at Los Alamos.

Thermonuclear weapons followed — fusion rather than fission, with yields hundreds or thousands of times greater. The largest ever tested, the Soviet Tsar Bomba in 1961, had a yield of around 50 megatons, roughly 3,000 times Hiroshima.

And the arsenals grew to a global peak of over 60,000 warheads in the 1980s.

Mutual assured destruction became the doctrine: if both sides can destroy the other after absorbing a first strike, neither can gain by striking first. It requires a survivable second-strike capability, which is why submarines matter so much.

Whether it worked is unfalsifiable and there has been no war between nuclear-armed great powers.

The near-misses are documented and they are the reason for caution. Stanislav Petrov, a Soviet officer, correctly judged a satellite warning of an American launch to be a false alarm in 1983 and did not report it up the chain. Vasili Arkhipov refused to authorise a nuclear torpedo launch from a Soviet submarine during the Cuban Missile Crisis when two of the three required officers had agreed (Chapter 12.2). The system depended, twice, on one person's judgement.

And there are documented false alarms from training tapes loaded by mistake, from a rising moon, and from a flock of geese.

Where this shows up in your life

Nine states possess nuclear weapons: the United States, Russia, Britain, France, China, India, Pakistan, Israel — which does not confirm it — and North Korea.

India's position is covered in Chapter 6.26: tests in 1974 and 1998, a declared no-first-use policy, and an arsenal justified as a deterrent against two nuclear-armed neighbours.

The Non-Proliferation Treaty of 1968 froze the nuclear club at five and committed those five to eventual disarmament — a commitment on which progress has been limited, which is the standing grievance of the non-nuclear states and the basis of India's long refusal to sign it as discriminatory.

Arsenals have fallen substantially from the Cold War peak and modernisation programmes are underway in every possessor state, and the arms control treaties that constrained them have been lapsing.

And the scientific point that closes the chapter. Nuclear weapons are the clearest case in this volume of a capability that cannot be uninvented. The physics is known and published. What restrains it is entirely political — treaties, verification, deterrence, and the taboo against use that has held for eighty years. All three are human arrangements, and Chapter 16.5 treats the maintenance of that taboo as one of the two or three things that most matter for whether this story continues.

What the next page covers

The wars are only part of the century's toll. Chapter 11.11 covers the other catastrophes — the famines that were policy, the purges, the genocides in Armenia, Cambodia, Rwanda and Bosnia, and the pattern common to them, which is specific enough to be recognised in advance.