American Scientist

DURING MY MANY YEARS TEACHING PHYSICS, I offered a general-education course on the Manhattan Project, which developed the first nuclear weapons during World War II. Most who took this course were nonscience students satisfying a physical-science graduation requirement. The first half of the course was devoted to describing relevant background discoveries: X-rays, radioactivity, protons and neutrons, atomic structure, isotopes, nuclear reactions, and associated technology. This material set the stage for a discussion about the discovery of fission, and it also had the purpose of helping students appreciate that nuclear weapons were not just dreamt up by a few people chatting around a coffeepot: They represent the culmination of a lengthy chain of discoveries, many of them serendipitous. When the course moved on to the Manhattan Project proper, we stressed the numerous organizational, logistical, and technical hurdles that were overcome and how any one of them might have derailed the Project entirely or resulted in it becoming a monumental boondoggle. Then we came to the bombings of Hiroshima and Nagasaki. These students had no direct experience with World War II, so I had to establish the context of the war in the summer of 1945: The high-casualty campaigns against Japanese-held islands in the Pacific, the relentless conventional and firebombing raids on Japan, plans for an invasion of the Japanese home islands and associated casualty projections, and the debates within American political, military, and scientific circles as to whether atomic bombs should be used directly against Japanese cities or whether a warning or demonstration should be offered first.

After describing the context and effects of the bombings (both physical and political), I always asked students for their opinions on the use of the bombs. Although I would receive a variety of comments, I was always somewhat frustrated in that I could never stimulate as much conversation and feedback as I felt this momentous history deserved. Perhaps this outcome is not surprising: None of them had studied either the science or the history closely, and, busy with other courses and commitments, they had little time to internalize these long-ago events. Some might have heard stories from grandparents or great-grandparents, but we now live in an era in which collective memory of the world’s only nuclear war is fading rapidly. But the danger of nuclear conflict is still very much with us, as the recent false alarm about a nuclear missile supposedly headed for Hawaii has demonstrated.

I began to reflect on how I might better relate the story of Hiroshima and Nagasaki and the tumultuous summer of 1945. My students had looked at documents, invasion-plan maps, tables of casualty statistics, and contemporary film footage. But students benefit greatly from talking through difficult subjects with their peers, and the idea struck me of crafting a dialogue in which the information and arguments would come out of the mouths of speakers just like them.

In this resulting dialogue, three students, Robert, Lisa, and Pat, have just attended a lecture by a distinguished historian on the political and military circumstances of World War II in the summer of 1945 and the atomic bombings of Hiroshima and Nagasaki. Robert is a physics major. Lisa is studying linguistics. Pat is undeclared as yet, but as secretary-treasurer of the student council, which helped sponsor the lecture, took careful notes. They go for a late pizza. Their favorite server, Enrico, is on duty and knows their usual order: a beer for Robert, chianti for Lisa, brio for Pat, house salads, and three personal pizzas to share, regular, vegetarian, and Hawaiian.

Pat: That was a really fascinating talk. I never realized there were so many factors involved in the end of the war. Professor Beder certainly knows her stuff.

Lisa, nodding, sipping her drink: On the day the bomb was dropped on Hiroshima, my great-grandfather was boarding his troopship in San Francisco. He would have been part of the invasion. Instead, he was in the occupation force, and he came to appreciate Asian languages and culture. When I was a kid I would look through his books on languages, which my parents inherited and which surely influenced me. Apparently he always said, “Thank God for the Atomic Bomb.”

Robert, shaking his head while watching that on his beer settle: No. All respect to your great-grandfather, but the war would likely have been over by the time he got there. The Japanese were close to surrendering, and the bombings were moral crimes of the worst order. They were horrible perversions of magnificent physics.

Lisa: Close, maybe, but they hadn’t surrendered, and they diddled around for weeks about the surrender terms. The cables their ambassador in Moscow sent back to Tokyo were practically pleading for a clear decision.

Pat: The Russians were also diddling around, for their own purposes, waiting to get in on the spoils while continuing to receive food, oil, and weaponry under America’s lend-lease program.

Robert: The delay was mostly our fault. We never really defined unconditional surrender.

Lisa, sneering: Which any diplomat would know would provide the behind-the-scenes wiggle room to save the Emperor’s position. The Japanese were ridiculous in some of their ideas, like proposing to try their own war criminals and being responsible for their own disarmament.

Robert: Well, they didn’t insist on those conditions in the end. It was their national identity in the person of the Emperor that was their big concern. And then Secretary of State Byrnes struck that clause out of the Potsdam declaration. I wonder if he did that in the knowledge that the Japanese would reject it and that then they would be able to use the bomb, which was really to show the Russians who would be in charge after the war.

Pat: Byrnes was doing his political job, which was to protect Truman. This was a new president, basically untried in foreign relations, negotiating with Stalin and Churchill. Any public statement that could have been interpreted as compromise or vacillation would have been a disaster for him.

“On the day the bomb was dropped on Hiroshima, my great-grandfather was boarding his troopship in San Francisco.”

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Enrico brings their salads.

Lisa, grinding cheese, to Robert: You say the bombings were immoral. What about the firebombing of Tokyo, which they figure killed a hundred thousand people in one night? Or the Japanese treatment of Chinese civilians and prisoners? The war had reached such a horrendous state. I know you can’t justify one horror on the basis of others, but the fact was that thousands of Japanese civilians were already dying every day in bombing raids, on top of all the combat losses. Anything that would shorten the war by even one day had to be considered. One statistic from the United Nations that stuck with me is that in East Asia and the Pacific, some 400,000 people per month—combatants and civilians—were dying.

Robert, waving his fork: But these weren’t just bigger bombs. This was an entirely new order of magnitude, wiping out an entire city at once. Horrible blast and burn injuries, then the radiation. You would have no chance to escape. We should at least have given the Japanese a clear warning or a demonstration.

Pat, flipping through notes: Well, they did consider a demonstration. There was this—okay, here it is—the Interim Committee, for which Oppenheimer and other scientists were called in as consultants. They discussed it but came up with various arguments against the idea, like what if it was a dud and the Japanese recovered it, and concern about wasting any of the small supply of fissile material. Even the scientists said that they couldn’t conceive of a demonstration likely to bring an end to the war.

Robert, sneering: Of course not. I understand this perfectly. I know many scientists were concerned with what using the bombs would do to our moral position. But I bet there were many who wanted to do their big experiment and show how they could help win the war. It’s easy to get consumed by the technology. Its use was a foregone conclusion.

Lisa, jumping in: But do you think the political and military people that were in charge weren’t going to use the bomb once it was ready, no matter what the scientists thought? Be realistic! It’s easy to sit in your office or lab and moralize while thousands of people are dying every day. The casualties in an invasion would have been horrific. Truman had to think about both the war situation and dealing with Russia afterward. It seems to me that the bombs got two birds with one stone—Japan and Russia. It wasn’t a binary choice, as some historians try to present it. Once the political machinery had hold of these things, the decisions were fundamentally out of the scientists’ hands.

Robert: Well, there was a lot of debate about predicted invasion casualties. As a matter of pure numbers, I don’t think it was at all clear that invasion casualties would have exceeded the casualties caused by the bombings. But numbers alone don’t address the moral point.

Pat, scanning notes: I tried to keep track of some of the most notable estimates. There were so many. The War and Navy Departments prepared their own estimates, then there were also estimates from the Joints Chiefs of Staff and the Combined Chiefs of Staff, and other estimates came up from field commanders and every office that wanted a piece of the action. Lots of bureaucratic infighting, and it would all get revised constantly as intelligence on the Japanese home-islands defense situation evolved.

Robert: So, for comparison, how big would the invasion have been?

Pat: There were actually going to be two. Operation Olympic was the planned invasion of Kyushu, the southern island of Japan, scheduled for the first of November. Nearly 800,000 ground troops were to be landed over the first forty-five days to bring the invasion force up to full strength. That doesn’t count all the offshore naval support and onshore ground support people. That force was to advance about a third of the way along the island, about 60 miles or so, setting up airbases that would support more bombing raids and for the second invasion, Operation Coronet, which would have taken place near Tokyo in March of 1946. That was to involve landing more than a million troops.

Lisa: My God.

Robert: By then the war would surely have been over.

“It’s easy to sit in your office or lab and moralize while thousands of people are dying every day.”

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Enrico clears their salads and sets down their pizzas. Everybody digs in.

Lisa, shaking her head: Sure, probably it would have been over by then, especially if the Russians had come in. But even if it had gone on for just a couple months after the first invasion, the casualties could have been horrendous. Three-quarters of a million troops—that would have dwarfed the invasion of Normandy.

Pat, spearing a wayward slice of tomato: Yes. On D-Day alone some 156,000 troops were landed. By five days later, the total was up to about 326,000. But they had the advantage of operating from England. For Japan, supply lines would have been across the entire Pacific. The logistics would have been immense.

Robert: What about the casualty projections for Japan?

Pat, reviewing notes: They were all over the place. Usually they came from extrapolating ratios from previous campaigns. One number that got a lot of currency was a half-million deaths, based on the Army’s kill ratio on Saipan: an average of one American killed and several wounded to kill seven Japanese soldiers. An August 1944 report extrapolated this to an expected number of Japanese home-island defenders of three and a half million, and that estimate got repeated a lot thereafter.

Lisa, putting down her pizza to make air quotes: “Kill ratio”—what a charming term.

Robert: But some estimates were a lot less than a half-million. That might have been on the high end.

Pat: Well, in June, 1944, General MacArthur estimated that 105,000 casualties—that is, dead and wounded—would occur over the first 90 days of Olympic.

Lisa: Over only 90 days? An invasion might have gone on for months beyond that. I wonder if he lowballed that for political purposes?

Pat: The lowest number I came across was given at the Joint Chiefs meeting with the President on June 18, 1945, exactly four weeks before the Trinity test. A report to the President estimated that casualties in the first 30 days of Olympic wouldn’t exceed those for the island of Luzon, which totaled 31,000. Japanese casualties there were more than 150,000. At the same meeting, Admiral King estimated that the figure would lie between those for Luzon and Okinawa, which were very similar. He didn’t say what span of time this was for. At Normandy there were 42,000 casualties during the first thirty days, so it surprised me that they expected Kyushu to be less. The Secretary of War felt it would be deplorable if an invasion had to go ahead.

Lisa: Now we’re down to just 30 days.

Robert: Who was this Admiral King?

Pat: Ahh. Let’s see—oh, Commander in Chief of the entire U. S. Fleet.

Lisa: Can you imagine being Truman at that meeting? His head must have been spinning.

Enrico checks on their dinners.

IN THEIR DISCUSSION SO FAR, the students have alluded to a number of scientific and technical issues that came up in the Manhattan Project. The vast majority of the cost of the Project went into building enormous facilities to isolate and synthesize fissile material. At Oak Ridge, Tennessee, three different factory complexes were constructed to separate the fissile isotope of uranium, uranium-235 (U-235), from its much more common sister isotope, uranium-238 (U-238). By mid-1945, after over two years of work, about 60 kg of U-235 had been isolated, which was enough for one bomb. This material would be used in the “Little Boy” bomb dropped on Hiroshima. Due to the scarcity of U-235, the uranium bomb was not tested before being deployed. At Hanford, Washington, three large nuclear reactors were used to transmute U-238 into plutonium-239 (Pu-239), which is also fissile. Once the reactors were in full-power operation and chemical techniques had been perfected to extract the synthesized plutonium from uranium fuel slugs, Hanford could generate enough Pu-239 for one bomb about every 10 days. By August 1945, enough plutonium was on hand for three bombs. The concern with consuming precious fissile material in a demonstration which might have no effect on Japanese decision-makers was very real.

The Interim Committee was established by Secretary of War Henry Stimson for the purpose of providing guidance on atomic policy until Congress could establish a more permanent committee after the war. Robert Oppenheimer, Enrico Fermi, Ernest Lawrence, and Arthur Compton served as members of an advisory Scientific Panel. These men represented the major scientific components of the bomb-making effort. Oppenheimer directed the Los Alamos laboratory, where the bombs were designed. Lawrence oversaw the development of one of the technologies used at Oak Ridge: Employing large-scale mass spectrometers to separate ionized uranium isotopes. Fermi and Compton were intimately involved in the development of reactor technology.

Ultimately, the vast majority of victims at Hiroshima and Nagasaki succumbed to burns and blast effects; it is estimated that only about 15 percent of prompt deaths were due to radiation exposure.

Pat, cutting another piece of pizza: Fast forward a month to the Potsdam Conference, where Admiral Nimitz’s estimate of 49,000 casualties was discussed, again in the first thirty days. Truman later claimed that General Marshall had told him that to take the area around Tokyo might cost a quarter-million to a million casualties. And then MacArthur generated a new estimate of about 125,000 by the time of Operation Coronet, and about three times that if nonbattle casualties were included. Another staff estimate was based on an estimate of 40,000 battle casualties sustained per two-and-a-half Japanese divisions. By late July 1945, Japanese strength in Kyushu was estimated to be thirteen divisions, which implied about 200,000 casualties there alone.

Robert, looking at Lisa: I keep telling you, it’s not just about numbers, it’s the moral ...

Lisa, shaking her head: It sure as hell is about the numbers if you are on a beach somewhere or are a civilian in a Japanese city. Are you saying that to lose a couple of hundred thousand people by firebombings or by having their guts blown out is somehow preferable to losing, say, half as many in an atomic explosion? This is just moral relativism.

Robert: It’s the total abandonment of any moral foundation that concerns me. With that logic you can justify anything. The bombs were just heinous, especially with the Japanese so close to surrendering.

Lisa, testily: But they still hadn’t. Glancing at Pat: What were the Hiroshima and Nagasaki statistics?

Pat: The highest numbers were in the Strategic Bombing Survey report of 1947, which indicated that 125,000 people were killed and up to 160,000 injured by the two bombings. Incidentally, one other number that seems pretty secure is that the Army, the Navy, and the Marine Corps were planning on needing to call up a combined total of about 141,000 men per month. That must give some idea of the expected replacement demands.

Robert: What were the Normandy casualty statistics?

Pat, consulting notes: Well, for the entire battle of Normandy, which went from D-Day to the capture of Paris in late August, some 425,000 people were killed or wounded or went missing. That’s the estimate for the two sides combined, with about 209,000 on the Allied side.

Lisa: So over a period of about ten weeks you already have far more than just the atomic bombing casualties alone, and from combatants only—not counting civilians lost in continuing bombing raids. It’s hard for me to imagine that if the invasion of Japan had gone on longer, there would have been fewer casualties over the same time, given the ferocity of Japanese resistance. Remember the 400,000-per-month statistic? Then add in all the complications of the Russians being in on the occupation.

Robert: But many of the casualty estimates were well below that. You can’t cherry-pick your numbers.

Lisa: Neither can you, because many were higher. And if we pride ourselves on our humanity, we shouldn’t ignore Japanese casualties. We can’t let ourselves slide into revisionist thinking.

Robert: What do you mean?

Lisa: I mean that you are a scientist and so you know that numbers do matter. But then you focus on a low one, or appeal to the uncertainty, or protest that the Japanese were (air quotes) “about to” surrender, which maybe seems much clearer now than it did at the time, when nobody knew which faction held the upper hand in the Japanese War Council. Then you leap to a moral argument that seems shaky, given what had already been done in the war by both sides. Maybe morality in war is different from that in peace. But in the end, what ratio of nonatomic to atomic casualties are you willing to put as the limit beyond which the immorality of the one finally outweighs the other? One to one? Ten? A hundred? Infinity? I think a lot of the so-called controversy about the use of the bombs is just made up by historians who are trying to impress tenure committees.

Robert: Now look who’s talking about moral relativism! But what about Truman? Do you really think the people making these decisions had any clue as to what the bombs would do?

Lisa: You ignored my question, but yes, I do think they knew. General Groves and Secretary of State Stimson briefed Truman on the whole project just after he became President, and Stimson said it could be the most terrible weapon ever known in human history. At that first meeting of the Interim Committee, the one that included the scientists, Stimson said the project should not be considered simply in terms of weapons, but as a new relationship of man to the universe. These don’t strike me as the words of people who didn’t have some sense of the magnitude of what they were dealing with. Besides, Truman was ultimately responsible for preventing any Allied casualties that he reasonably could.

Pat: He also wrote in his diary of how powerful the Trinity test was, and he heard General Groves’s report on it when he was in Potsdam. He certainly seemed to be impressed by it.

Lisa: And he ordered a stop to any more atomic bombings after Nagasaki, telling his Cabinet that the thought of wiping out another 100,000 people was just too horrible. I think this shows his fundamental humanity.

Robert: Yeah, after the second bomb. The first was bad enough, maybe arguably justified by some perverse logic, but was there any real justification for the second? At least anything beyond justifying the cost of the project, and threatening Russia?

Lisa: I think so. Okay, maybe they could have waited a few more days to give the Japanese time to assess it, but it showed that Hiroshima wasn’t just a one-off piece of luck—that America could make more than one of these things, and that no country without the atomic bomb could hope to win against a country that had it. That was one of the arguments used by the peace faction in the Japanese Cabinet in the debates about surrendering.

Pat: After the second bomb the psychological shock value was lost. They would have had another one ready in about a week, and as many as about twenty by the end of the year, but General Marshall was already considering reserving them for tactical use to support the invasion. If that had happened, the radiation exposure statistics could have been horrendous.

Lisa, looking at Robert: You never really answered my question about other forms of death being more morally defensible than one by an atomic bombing.

“I know that Truman had to end the war and that none of his options were very nice.”

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Robert: The thing is that when something gets escalated like this, like the firebombings, which were horrific enough, then it becomes normalized and it inevitably becomes easier to justify something worse. The scientists’ petition about how the Japanese should be offered a chance to surrender before the bomb was used was basically ignored by those in power. I just don’t get the sense that the idea of a demonstration or proper warning was given the level of consideration it should have been.

Lisa: I don’t think it was totally ignored. Stimson was told about their concern that using the bomb might sacrifice our whole moral standing when it came to proposing any system of international control. But in the end his job was to conclude the war as soon as possible.

Pat: Anyway, the people in power didn’t all think the same way. One of the members of the Interim Committee— the Undersecretary of the Navy, Ralph Bard—sent a memo to the President before the Trinity test urging that the Japanese be warned about the possible use of nuclear weapons and that the status of the Emperor be clarified.

Lisa: The scientists weren’t all in agreement either. In the Chicago Metallurgical Lab poll, some of them felt the weapons should be used directly, and almost half thought that there should be a so-called military demonstration in Japan.

Pat: It’s not clear to me what the term “military demonstration” meant. I guess exploding it in a remote area but where observers could see it.

Enrico discreetly places their bill so that it is equidistant from the three of them. Tradition is to effect a trinary fission.

Lisa: Also, the whole international control thing advocated by the scientists strikes me as a fantasy. I know it was considered at high levels, but do you really think the Russians would have ever agreed to such a thing except maybe as a delaying tactic while they worked on their own bomb? And I can’t imagine our side being too eager to share scientific data, with the Cold War brewing. Look, while the negotiations were going on in 1946, we set off nuclear tests at the Bikini Atoll.

Robert, fishing through his wallet: You see? That’s yet more normalization. But you’re right about the hypocrisy on both sides. I know that Truman had to end the war and that none of his options were very nice, but I can’t forgive him for not giving the Japanese a fair warning. To throw the bomb on them like that was just inhumane, no matter what atrocities they had perpetrated during the war and no matter what remorse prompted his later decision.

Pat, chipping in: I think there is a point here that has been overlooked. Suppose that the bombs hadn’t been developed in time for use in the war, or they weren’t used and the world had remained uninformed as to how awful they are? What might have happened in a later war when there were more of them held by more countries and they were more powerful? Then it could have been really horrific. Maybe in some perverse way Hiroshima and Nagasaki have given us a shot of nuclear inoculation over all these decades, and have prevented even worse moral atrocities.

Robert, pausing and then draining his beer: I hadn’t thought of that.

Lisa adds her share of the bill and absentmindedly straightens the pile: Hunh.

Robert, continuing: But we still could have given the world a demonstration. Too bad history isn’t like a computer program where we could rerun it with different choices and see what happens.

Lisa, returning her wallet to her purse: But this is assuming the leaders of these countries are fundamentally rational people. That the President of Russia isn’t going to sacrifice Moscow for New York, or vice versa. And also that the command structures are stable and the weapons secure. In some places now, I’m not really sure these conditions hold any more. A lunatic terrorist or sympathizer isn’t bound by such constraints. It’s scary.

Pat: It is scary, and there are still thousands of these things out there. It’ll be decades more before we get rid of them all, if ever. If any of us ever have kids, they’ll inherit all this.

Robert: We can’t uninvent nuclear physics. Discoveries will always go on, and I admit I want to be part of that business.

Pat: All this was born with the discovery of fission; somebody would have discovered it sooner or later. I wonder what might have happened if it had been discovered by Fermi in 1934? But that’s the way it is. Like anything, it’s what we make of it.

Robert, donning his coat: I guess. Well, I’ll see you guys tomorrow. I have Professor Raj’s statistical mechanics class at eight-thirty in the morning!

Lisa, Pat: Okay. See you.

THE TRINITY TEST, which took place on July 16, 1945, was a test of the design of the plutonium bomb. Conducted in southern New Mexico, this test yielded an explosive energy equivalent to detonating about 20,000 tons of TNT. Three weeks later, the “Fat Man” plutonium bomb was dropped on Nagasaki. The “Metallurgical Laboratory” was a code name for the Manhattan Project’s offices and laboratories located at the University of Chicago, where Fermi, Compton, and many others directed reactor development. In the summer of 1946, the United Nations Atomic Energy Commission held hearings on possible international control of fissile materials and nuclear energy, but these discussions foundered in the face of the growing Cold War.

The last part of the discussion alludes to a number of issues that are still with us. By no means did nuclear weapons become obsolete with the end of the Cold War. The United States and Russia each boast about 2,000 weapons on deployed status, with about as many in ready reserve. Both countries also hold over 2,000 more “retired” weapons awaiting dismantlement. Stockpiles in other countries (Britain, France, China, India, Pakistan, and North Korea) amount to about 1,000 more. These bombs have yields up to tens of times those used in World War II. According to a recent Department of Defense Nuclear Posture Review, the United States is projected to spend over a trillion dollars over the next 30 years to upgrade existing weapons and delivery systems. Of particular concern in nonproliferation circles is the proposed development of new models of low-yield “tactical” nuclear weapons, which could lower the psychological threshold against use. The International Panel on Fissile Materials estimates that the world supply of highly-enriched uranium amounts to some 1,300 tons, and the supply of separated plutonium to some 500 tons. Most of this supply is in the hands of the United States and Russia; although some is being blended into reactor fuel, this material will need to be secured for decades. At Hanford, cleanup of environmental damage caused by wastes generated during decades of fissile materials production will itself take decades and costs hundreds of billions of dollars. For students of science, strategy, and policy, there is plenty of work to be done in the nuclear arena.