Posts Tagged ‘Nagasaki’

Meditations

Were there alternatives to the atomic bombings?

Monday, August 3rd, 2015

As we rapidly approach the 70th anniversary of the bombings of Hiroshima and Nagasaki, there have been all sorts of articles, tributes, memorials, and so forth expressed both in print and online. I’ve been busy myself with some of this sort of thing. I was asked if I would write up a short piece for Aeon Ideas about whether there were any alternatives to these bombings, and I figure it won’t hurt to cross-post it here as well.

Unusual photograph of the late cloud of Hiroshima, as seen from the air. This was probably taken by aircraft that arrived several hours after the bombing to do damage reconnaissance; they reported the target was obscured by huge amounts of smoke. Source: National Archives and Records Administration, via Fold3.com.

An unusual photograph of the late clouds of Hiroshima, as seen from the air. This was probably taken by aircraft that arrived several hours after the bombing to do damage reconnaissance; they reported the target was obscured by huge amounts of smoke. Source: National Archives and Records Administration, via Fold3.com.

The point of the piece, I would like to emphasize, is not necessarily to “second guess” what was done in 1945. It is, rather, to point out that we tend to constrain our view of the possibilities generally to one of two unpleasant options. Many of those who defend the bombings seem to end up in a position of believing that 1. there were no other options on the table at the time except for exactly what did occur, and 2. that questioning whether there were other options does historical damage. As a historian, I find both of these positions absurd. First, history is full of contingency, and there were several explicit options (and a few implicit ones) on the table in 1945 — more than just “bomb” versus “invade.” These other options did not carry the day does not mean they should be ignored. Second, I think that pointing out these options helps shape our understanding of the choices that were made, because they make history seem less like a fatalistic march of events. The idea that things were “fated” to happen the way they do does much more damage to the understanding of history, because it denies human influence and it denies choices were made.

Separately, there is a question of whether we ought to “judge” the past by standards of the present. In some cases this leads to statements that are simply non-sequiturs — I think Genghis Khan’s methods were inhumane, but who cares that I think that? But World War II was not so long ago that its participants are of another culture entirely, and those who say we should not judge the atomic bombings by the morality of the present neglect the range of moral codes that were available at the time. The idea that burning civilians alive created a moral hazard was hardly unfamiliar to people in 1945, even if they did it anyway. Similarly, I will note that the people who adopt such a position of historical moral relativism never seem to apply it to nations that fought against their countries in war.

Anyway, all of the above is meant as a disclaimer, in case anyone wonders what my intent is here. It is not to argue that the leaders of 1945 necessarily ought to have done anything different than they did. It is merely to try and paint a picture of what sorts of possibilities were on the table, but were not pursued, and to try and hack away a little bit at the false dichotomy that so often characterizes this discussion — a dichotomy, I might note, that was started explicitly as a propaganda effort by the people who made the bomb and wanted to justify it against mounting criticism in the postwar. I believe that rational people can disagree on the bombings of Hiroshima and Nagasaki.


What options were there for the United States regarding the atomic bomb in 1945?

Few historical events have been simultaneously second-guessed and vigorously defended as the atomic bombings of Hiroshima and Nagasaki, which occurred seventy years ago this August. To question the bombings, one must assume an implicit alternative history is possible. Those who defend the bombings always invoke the alternative of a full-scale invasion of the Japanese homeland, Operation Downfall, which would have undoubtedly caused many American and Japanese casualties. The numbers are debatable, but estimates range from the hundreds of thousands to the millions — an unpalatable option, to be sure.

These unusual before-and-after images come from the Report of the Joint Commission for the Investigation of the Effects of the Atomic Bomb on Japan, Volume I, "Medical Effects of Atomic Bombs," NP-3036 (April 1951). I apologize for the poor image quality. I thought that even so they provide striking contrasts, and are much more easy to grasp that the familiar "view from above" photographs. This one is of the Hiroshima Commercial Museum, only 300 m from ground zero, and now known as the famous "Genbaku dome."

These unusual before-and-after images come from the Report of the Joint Commission for the Investigation of the Effects of the Atomic Bomb on Japan, Volume I, “Medical Effects of Atomic Bombs,” NP-3036 (April 1951). I apologize for the poor image quality. I thought that even so they provide striking contrasts, and are much more easy to grasp that the familiar “view from above” photographs. This one is of the Hiroshima Commercial Museum, only 300 meters from Ground Zero, and now known as the famous “Genbaku dome.” The photographs are not labeled with when they were taken; the “before” photos seem like they are from the late 1930s, the “after” photos are likely no earlier than September 1945, and may be from 1946.

But is this stark alternative the only one? That is, are the only two possible historical options available a bloody invasion of the Japanese home islands, or the dropping of two nuclear weapons on mostly-civilian cities within three days of one another, on the specific days that they were dropped? Well, not exactly. We cannot replay the past as if it were a computer simulation, and to impose present-day visions of alternatives on the past does little good. But part of the job of being a historian is to understand the variables that were in the air at the time — the choices, decisions, and serendipity that add up to what we call “historical contingency,” the places where history could have gone a different direction. To contemplate contingency is not necessarily to criticize the past, but it does seek to remove some of the “set in stone” quality of the stories we often tell about the bomb.

Varying the schedule. The military order that authorized the atomic bombings, sent out on July 25, 1945, was not specific as to the timing, other than saying that the “first special bomb” could be dropped “as soon as weather will permit visual bombing after about 3 August 1945.” Any other available bombs could be used “as soon as made ready by the project staff.” The Hiroshima mission was delayed until August 6th because of weather conditions in Japan. The Kokura mission (which became the Nagasaki mission) was originally scheduled for August 11th, but got pushed up to August 9th because it was feared that further bad weather was coming. At the very least, waiting more than three days after Hiroshima might have been humane. Three days was barely enough time for the Japanese high command to verify that the weapon used was a nuclear bomb, much less assess its impact and make strategic sense of it. Doing so may have avoided the need for the second bombing run altogether. Even if the Japanese had not surrendered, the option for using further bombs would not have gone away. President Truman himself seems to have been surprised by the rapidity with which the second bomb was dropped, issuing an order to halt further atomic bombing without his express permission.

"Komiya street (750 meters [from Ground Zero] before and after bombing. The archlike heavy lamp posts have fallen. One lies at the left of the lower photograph."

“Komiya street (750 meters [from Ground Zero] before and after bombing. The archlike heavy lamp posts have fallen. One lies at the left of the lower photograph.”

Demonstration. Two months before Hiroshima, scientists at the University of Chicago Metallurgical Laboratory, one of the key Manhattan Project facilities, authored a report arguing that the first use of an atomic bomb should not be on an inhabited city. The committee, chaired by Nobel laureate and German exile James Franck, argued that a warning, or demonstration, of the bomb on, say, a barren island, would be a worthwhile endeavor. If the Japanese still refused to surrender, then the further use of the weapon, and its further responsibility, could be considered by an informed world community. Another attractive possibility for a demonstration could be the center of Tokyo Bay, which would be visible from the Imperial Palace but have a minimum of casualties if made to detonate high in the air. Leo Szilard, a scientist who had helped launch the bomb effort, circulated a petition signed by dozens of Manhattan Project scientists arguing for such an approach. It was considered as high as the Secretary of War, but never passed on to President Truman. J. Robert Oppenheimer, joined by three Nobel laureates who worked on the bomb, issued a report, concluding that “we can propose no technical demonstration likely to bring an end to the war; we see no acceptable alternative to direct military use.” But was it feasible? More so than most people realize. Though the US only had two atomic bombs in early August 1945, they had set up a pipeline to produce many more, and by the end of the month would have at least one more bomb ready to use, and three or four more in September. The invasion of the Japanese mainland was not scheduled until November. So by pushing back the time schedule, the US could have still had at least as many nuclear weapons to use against military targets should the demonstration had failed. The strategy of the bomb would have changed — it would have lost some of its element of “surprise” — but, at least for the Franck Report authors, that would be entirely the point.

Changing the targets. The city of Hiroshima was chosen as a first target for the atomic bomb because it had not yet been bombed during the war (and in fact had been “preserved” from conventional bombing so that it could be atomic bombed), because the scientific and military advisors wanted to emphasize the power of the bomb. By using it on an ostensibly “military” target (they used scare quotes themselves!), “located in a much larger area subject to blast damage,” they hoped both to avoid looking bad if the bombing was somewhat off-target (as the Nagasaki bombing was), and so that the debut of the atomic bomb was “sufficiently spectacular” that its importance would be recognized not only by the Japanese, but the world at large. But the initial target for the bomb, discussed in 1943 (long before it was ready) was the island of Truk (now called Chuuk), an ostensibly purely military target, the Japanese equivalent of Pearl Harbor. By 1945, Chuuk had been made irrelevant, and much of Japan had already been destroyed by conventional bombing, but there were other targets that would not have been so deliberately destructive of civilian lives. As with the “demonstration,” option had the effect not been as desired, escalation was always available as a future option, rather than as the first step.

"Prefectural Office (900 meters [from Ground Zero]) before and after the bombing. The wooden structure has collapsed and burned. Note displacement of the heavy granite blocks of the wall."

“Prefectural Office (900 meters [from Ground Zero]) before and after the bombing. The wooden structure has collapsed and burned. Note displacement of the heavy granite blocks of the wall.”

Clarifying the Potsdam Declaration. By the summer of 1945, a substantial number of the Japanese high command, including the Emperor, were looking for a diplomatic way out of the war. Their problem was that the Allies had, with the Potsdam Declaration, continued to demand “unconditional surrender,” and emphasized the need to remove “obstacles” preventing the “democratic tendencies” of the Japanese people. What did this mean, for the postwar Japanese government? To many in the high command, this sounded a lot like getting rid of the Imperial system, and the Emperor, altogether, possibly prosecuting him as a “war criminal.” For the Japanese leaders, one could no more get rid of the Emperor system and still be “Japan” than one could get rid of the US Constitution and still be “the United States of America.” During the summer, those who constituted the “Peace Party” of the high council (as opposed to the die-hard militarists, who still held a slight majority) sent out feelers to the then still-neutral Soviet Union to serve as possible mediators with the United States, hopefully negotiating an end-of-war situation that would give some guarantees as to the Emperor’s position. The Soviets rebuffed these advances (because they had already secretly agreed to enter the war on the side of the Allies), but the Americans were aware of these efforts, and Japanese attitudes towards the Emperor, because they had cracked the Japanese diplomatic code. No lesser figures than Winston Churchill and the US Secretary of War, Henry Stimson, had appealed to President Truman to clarify that the Emperor would be allowed to stay on board in a symbolic role. Truman rebuffed them, at the encouragement of his Secretary of State, James Byrnes, believing, it seems, that the perfidy of Pearl Harbor required them to grovel. It isn’t clear, of course, that this would have changed the lack of a Japanese response to the Potsdam Declaration. Even after the atomic bombings, the Japanese still tried to get clarification on the postwar role of the Emperor, dragging out hostilities another week. In the end, the Japanese did get to keep a largely-symbolic Emperor, but this was not finalized until the Occupation of Japan.

Waiting for the Soviets. The planned US invasion of the Japanese homeland, Operation Downfall, was not scheduled to take place until early November 1945. So, in principle, there was no great rush to drop the bombs in early August. The Americans knew that the Soviet Union had, at their earlier encouragement, agreed to renounce their Neutrality Pact with the Japanese and declare war, invading first through Manchuria. Stalin indicated to Truman this would happen around August 15th, to which Truman noted in his diary, “Fini Japs when that comes about.” Aside from cutting Japan off from its last bastion of resources, the notion of possibly being divided into distinct Allied zones of influence, as had been Germany, would possibly be more of a direct existential threat than any damage the Americans would inflict. And, in fact, we do now know that the Soviet invasion may have weighed as heavily on the Japanese high command as did the atomic bombings, if not more so. So why didn’t Truman wait? The official reason given after the fact was that any delay whatsoever would be interpreted as wasting time, and American lives, once the atomic bomb was available. But it may also have been because Truman, and especially his Secretary of State, Byrnes, may have hoped that the war might have ended before the Soviets had entered. The Soviets had been promised several concessions, including the island of Sakhalin and the Kuril Islands (giving them unimpeded access to the Pacific Ocean) for their entry in the war, but by late July 1945, the Americans were having second thoughts. As it was, once Stalin saw that Hiroshima did not provoke an immediate response from the Japanese, he had his marshals accelerate the invasion plans, invading Manchuria just after midnight, the morning of the Nagasaki bombing.

I find this one to be one of the most haunting — by filling in the missing structures, it contextualizes all of the "standard" Hiroshima photos of the rubble-filled wasteland. "Rear view of Geibi and Sumitomo Buildings before and after bombing. Taken from Fukuya Department Store (700 meters [from Ground Zero]) looking toward center. Complete destruction of wooden buildings by blast and fire. Concrete structures stand." In other places in the text, they usually point out that where you see a concrete structure like this, it has withstood the blast but was gutted by the fire.

I find this one to be one of the most haunting — by filling in the missing structures, it contextualizes all of the “standard” Hiroshima photos of the rubble-filled wasteland.
“Rear view of Geibi and Sumitomo Buildings before and after bombing. Taken from Fukuya Department Store (700 meters [from Ground Zero]) looking toward center. Complete destruction of wooden buildings by blast and fire. Concrete structures stand.” In other places in the text, they usually point out that where you see a concrete structure like this, it has withstood the blast but was gutted by the fire.

What should we make of these “alternatives”? Not, necessarily, that those in the past should have been clairvoyant. Or that their concerns were ours: like it or not, those involved in these choices certainly ranked Japanese civilian lives lower than those of American soldiers, as is typical in war. None of the “alternatives” come with any confidence, even today, much less for those at the time, and those making the choices were working with the requirements, uncertainties, and biases inherent to their historical and political positions.

But by pointing out the alternatives that were on the table, one can see the areas of choice and discretion, the different directions that history might have gone — perhaps for better, perhaps for worse. We should see this history less as a static set of “inevitable” events, or of “easy” choices, but as a more subtle collection of options, motivations, and possible outcomes.

Meditations

History in the flesh

Friday, May 29th, 2015

My main mode of interacting with history is through documents. Memos, reports, letters, telegrams, transcriptions, diagrams — the written word. The sociologist of science Bruno Latour calls these kinds of sources inscriptions, that which got written down, fixed into some kind of reproducible media. In Latour’s work, he emphasizes the act of inscription to highlight the gulf that exists between what gets written down and the anarchy of the raw, natural world. The inscription is a limited product of that raw world, a small subset of its multitudes of activities and phenomena and possibilities, and is always an incomplete lens by which to interrogate the world, but its very incompleteness allows it to be fixed, circulated, and analyzed. Without this act of inscription, science (and history) could not move forward, because there would be no such thing as the necessary “data.”

A small sampling of the sort of "inscriptions" I deal with regularly, the raw stuff of conjuring up the past: a typewritten report later turned into a microfilm entry (later scanned into a PDF file); a typewritten copy of a memo I got from an archive (later photographed by me and turned into a PDF); a hand-drawn diagram (evidence from the Rosenberg trial) that was later deposited into an archive (and later scanned as a TIF file).

A small sampling of the sort of “inscriptions” I deal with regularly, the raw stuff of conjuring up the past: a typewritten report later turned into a microfilm entry (later scanned into a PDF file); a typewritten copy of a memo I got from an archive (later photographed by me and turned into a PDF); a hand-drawn diagram (evidence from the Rosenberg trial) that was later deposited into an archive (and later scanned as a TIF file).

All of which might seem a little obvious once I say it. We need sources, of some sort, to do history? Tell me more. But the reason to point this out is to mention that historians are very aware that there’s lots of things that happened in the past that don’t get inscribed, and that the modes of inscription are not always reliable (even when people are trying to do their best, much less when they aren’t), and that the archive is just a proxy for understanding the past, and not in any way a full representation of the past. The job of the historian, stated in this way, is to piece together a fuller, more synthetic understanding of the past based on what is really a very shallow evidentiary base. We take half a dozen pieces of paper marked with symbols, and use those to try and conjure up an entire lost world. We take scribbles on paper and use them to try and reconstruct the subjective states of other human minds. When you put it like that, it is a pretty wonderfully mystical, kind of medieval, style of knowledge production. Which is why I love it — its flaws are obvious, its possibilities are endless, and it requires a very diverse group of skills that both empirical and creative.

But there are other ways to know the past. Being in the physical places of the past does seem to trigger a different response to it, as opposed to just reading about said places. This is one of the reasons I am so supportive of the Manhattan Project National Historic Park initiative. There is something about witnessing a historical landscape in person, that encourages a different sort of empathy with those who lived past, a seeing with other eyes.

A view from the car window, driving from Albuquerque to Santa Fe. One of about 10 million photographs I took on my trip. Eventually I will post some more. Separately, if you want a Los Alamos Ranch School mug, I was inspired to make them after my trip, and they are based on the actual seal of the school, which I saw for the first time while out there.

A view from the car window, driving from Albuquerque to Santa Fe. One of about 10 million photographs I took on my trip. Eventually I will post some more. Separately, if you want a Los Alamos Ranch School mug, I was inspired to make them after my trip, and they are based on the actual seal of the school, which I saw for the first time while out there.

I haven’t personally been to a lot of these Manhattan Project sites. Sometimes this surprises people, but it’s just been a matter of time and money. For my last Spring Break, though, I had the opportunity to spend a week in New Mexico, teaching a couple classes for my friend Luis Campos at the University of New Mexico (whose book on the history of radium was just published). My wife and I spent a few days in Santa Fe as a guest of the wonderful Cheryl Rofer, who also gave us the best unofficial tour of Los Alamos you could ask for, with assistance from Alan Carr (the Historian for Los Alamos National Laboratory) and the irrepressible Ellen Bradbury Reid, described aptly in an article as the “Eloise of Los Alamos,” which is a phrase I so wish I had come up with.

I had not previously spent too much time in the Southwest before. The landscape out there is stunning and other-worldly. On your left will be nothing but flat, scrubby desert. On your right, a towering mountain. Drive a little further and you find lushness and trees. Drive a little more and you find dryness and rock. Go up high enough and it might be snowing. Look around, feel the vastness of the area. Walk around and see the legacy of the three different peoples who have lived there: the Indians, the Spanish, the Anglos. It is an unusual place that feels as unlike the parts of California I am from as it does the East Coast urban metropolises I have lived for the last ten years. They don’t call it the “Land of Enchantment” for nothing.

All of which deepened, I like to believe, my feeling for Los Alamos during the war. What it must have meant to travel out there, to take the one good road from Santa Fe up onto the Mesa (there is a highway now, of course, but the old road is still there, albeit better paved). The way in which the various Technical Areas were nestled into the tree-lined valleys, and how you could go up those hills and look down on just miles and miles around. Today, of course, Los Alamos is a huge, sprawling laboratory. We didn’t really get to go inside of it to any real extent (there are a lot of rules governing that sort of thing), but Alan Carr took us up a hill which gave us great panoramas of the whole site. The hills around the lab are today full of dead, burned trees, the result of several forest fires that devastated them. But when you drive around the mesas near Bandelier National Monument, you get a sense for that rustic, rocky environment that so appealed to J. Robert Oppenheimer, that seemed such incredible contrast to his secular Jewish upbringing on Manhattan’s Upper West Side.

Nagasaki Mayor Tomihisa Taue, Atomic Heritage Foundation President Cynthia Kelly and Hiroshima Mayor Kazumi Matsui at the meeting in New York, just across from the United Nations building. I was sitting a little out of frame, near Mayor Matsui. Source: Japan Times.

Nagasaki Mayor Tomihisa Taue, Atomic Heritage Foundation President Cynthia Kelly and Hiroshima Mayor Kazumi Matsui at the meeting in New York, just across from the United Nations building. I was sitting a little out of frame, near Mayor Matsui. Source: Japan Times.

About a month afterwards, I had another unusual opportunity to experience history in the flesh. Connected with my work with the Atomic Heritage Foundation (I have joined their Advisory Committee), I was invited to take part in a meeting with the mayors of Hiroshima and Nagasaki, as well as several hibakusha, survivors of the atomic bombings.1 The Japanese delegation was in town for the NPT Review conference, but they wanted to meet with the Atomic Heritage Foundation in a public forum to talk about concerns they had with the Manhattan Project National Historic Park. Most of their concerns were understandable and shared by us: they want the history of the atomic bomb to not be presented in a celebratory mode, and to give credence to the many different perspectives that are held on it. They want the human consequences of the bombings to be made loud and clear. They want these sites to be places where people are encouraged to make up their own minds, rather than simply being told what to think about the past. On this I think everyone was in complete agreement. The details, of course, will be tricky in practice, but such is the nature of these things.

I had never seen hibakusha before, and I was greatly honored to meet them. There are not so many of them left. Many of those who are still alive, as with the remaining Holocaust survivors, were children during World War II. Which points, inadvertently, to the immense human costs of these events, to the innocents swept up into the maw of war. I have of course read much about the Japanese victims of the bomb, but it is another thing to meet them. The incident inspired me to re-read John Hersey’s Hiroshima for the first time in a long while, and the raw humanity of his account hit me in a way that it hadn’t before — the depth of my historical empathy increased measurably.

Which doesn’t tell one how to think about the use of the atomic bomb, I feel compelled to point out. Having sympathy and empathy with the past does not tell one which particular historical point of view one should subscribe to. There are many possible points of view to even non-controversial events, much less intensely controversial ones.2

Several of the still-living Manhattan Project veterans/

Several of the still-living Manhattan Project veterans. It is unclear how many of the nearly half-million people who worked on Manhattan Project are still alive. 

Next week (June 2-3, 2015), as part of a really wonderful symposium on the 70th Anniversary of the Manhattan Project hosted by the Atomic Heritage Foundation in Washington, DC, I will also get to spend some more time with other Manhattan Project veterans. These too are becoming an endangered species, along with all World War II-era veterans. It’s not the specific stories or experiences of these people that I often get the most out of. There’s something about just spending time around these historical actors (as historians like to call our human subjects) that helps you understand their world, remind you of the human content of the past.

If you are in town, the talks will be worth going to. Aside from my own talk (which will be great fun, I assure you), the other committed speakers include Kai Bird, Denise Kiernan, Robert S. Norris, Richard Rhodes, and Martin Sherwin. I have it on good authority that John Coster-Mullen will be in attendance, too. There is still time to register.

In a decade it will be the 80th anniversary of the Manhattan Project and World War II. There will probably not be any veterans to talk to then. There is an advantage to that, for the historian: living historical actors are tricky. They can disagree with you. Their individual perspectives can be intoxicating, charismatic, misleading. They can insist that their perspectives on history take precedence over the synthetic version you have constructed from inscriptions. They aren’t always right on that, as all history students are taught, but that doesn’t mean they can’t make trouble for you — the Smithsonian Enola Gay controversy in 1995 was one in part such a conflict of perspectives. It is in some ways easier to deal with the long-since deceased, because you can regard their inscriptions from something of a remove. But you do miss out on something, and its not just nostalgia. You have to work harder to reconstruct these other worlds, these other subjective states, in the absence of a working, functioning example sitting in front of you. This is why we have to preserve these spaces, and these voices, just as diligently as we have to preserve the documents, the inscriptions.

Notes
  1. Among other things, I learned that to an American ear, it is pronounced heh-bak-sha, with the u being essentially silent. []
  2. This was one of the great fallacies of the 1995 Enola Gay controversy — the idea that by talking about the victims of the bombs, you somehow took away from those who thought the bombs were necessary or important. History is complex, and we need to treat the audiences of history as if they were intelligent human beings capable of understanding multiple, possibly contradictory perspectives. If we don’t do that, we are just doing some form of crude activism for one cause or another, and the world has enough of that to go around as it is. []
Redactions

To demonstrate, or not to demonstrate?

Friday, March 6th, 2015

As the atomic bomb was becoming a technological reality, there were many scientists on the Manhattan Project who found themselves wondering about both the ethics and politics of a surprise, unwarned nuclear attack on a city. Many of them, even at very high levels, wondered about whether the very threat of the bomb, properly displayed, might be enough, without the loss of life that would come with a military attack.

1945-06-12 - Franck Report

The Franck Report, written in June 1945 by scientists working at the University of Chicago Metallurgical laboratory, put it perhaps most eloquently:

the way in which nuclear weapons, now secretly developed in this country, will first be revealed to the world appears of great, perhaps fateful importance. … It will be very difficult to persuade the world that a nation which was capable of secretly preparing and suddenly releasing a weapon, as indiscriminate as the rocket bomb and a thousand times more destructive, is to be trusted in its proclaimed desire of having such weapons abolished by international agreement…. 

From this point of view a demonstration of the new weapon may best be made before the eyes of representatives of all United Nations, on the desert or a barren island. The best possible atmosphere for the achievement of an international agreement could be achieved if America would be able to say to the world, “You see what weapon we had but did not use. We are ready to renounce its use in the future and to join other nations in working out adequate supervision of the use of this nuclear weapon.”

They even went so far as to suggest, in a line that was until recently totally etched out of the historical record by the Manhattan Project censors, that “We fear its early unannounced use might cause other nations to regard us as a nascent Germany.” 

The evolution of the "Trinity" test fireball, at constant scale, with the Empire State Building for additional scale reference.

The evolution of the “Trinity” test fireball, at constant scale, with the Empire State Building for additional scale reference.

The idea of a “demonstration” was for many scientists a compelling one, and news of the idea spread to the various project sites. The idea would be to let the Japanese know what awaited them if they did not surrender. This would be more than just a verbal or textual warning, which could be disregarded as propaganda — they would set the bomb off somewhere where casualties would be low or minimal, but its nature easy to verify. If the demonstration did not work, if the Japanese were not receptive, then the bomb could be used as before. In the eyes of these scientists, there would be no serious loss to do it this way, and perhaps much to gain.

Of course, not all scientists saw it this way. In his cover letter forwarding the Franck Report to the Secretary of War, the physicist Arthur Compton, head of the Chicago laboratory, noted his own doubts: 1. if it didn’t work, it would be prolonging the war, which would cost lives; and 2. “without a military demonstration it may be impossible to impress the world with the need for national sacrifices in order to gain lasting security.” This last line is the more interesting one in my eyes: Compton saw dropping the bomb on a city as a form of “demonstration,” a “military demonstration,” and thought that taking a lot of life now would be necessary to scare the world into banning these weapons in the future. This view, that the bombs were something more than just weapons, but visual arguments, comes across in other scientists’ discussions of targeting questions as well.

Truman was never asked or told about the demonstration option. It is clear that General Groves and the military never gave it much thought. But the Secretary of War did take it serious enough that he asked a small advisory committee of scientists to give him their thoughts on the matter. A Scientific Panel, composed of J. Robert Oppenheimer, Arthur Compton, Enrico Fermi, and Ernest Lawrence, weighed in on the matter formally, concluding that: “we can propose no technical demonstration likely to bring an end to the war; we see no acceptable alternative to direct military use.”1

"Recommendations on the Immediate Use of Atomic Weapons," by the Scientific Panel of the Interim Committee, June 16, 1945. The full report (which also discusses the possibility of the H-bomb and many other things) is extremely interesting, as well — click here to read it in its entirety.

“Recommendations on the Immediate Use of Atomic Weapons,” by the Scientific Panel of the Interim Committee, June 16, 1945. The full report (which also discusses the possibility of the H-bomb and many other things) is extremely interesting, as well — click here to read it in its entirety.

I find this a curious conclusion for a few reasons. For one thing, are these four scientists really the best experts to evaluate this question? No offense, they were smart guys, but they are not experts in psychological warfare, Japanese political thought, much less privy to intercepted intelligence about what the Japanese high command was thinking at this time. That four physicists saw no “acceptable alternative” could just be a reflective of their own narrowness, and their opinion sought in part just to have it on the record that while some scientists on the project were uncomfortable with the idea of a no-warning first use, others at the top were accepting of it.

But that aside, here’s the other fun question to ponder: were they actually unanimous in their position? That is, did these four physicists actually agree on this question? There is evidence that they did not. The apparent dissenter was an unlikely one, the most conservative member of the group: Ernest Lawrence. After the bombing of Hiroshima, Lawrence apparently told his friend, the physicist Karl Darrow, that he had been in favor of demonstration. Darrow put this into writing on August 9, 1945, to preserve it for posterity should Lawrence come under criticism later. In Darrow’s recollection, Lawrence debated it with the other scientists for “about an hour” — a long-enough time to make it seem contentious. On August 17, after the bomb had “worked” to secure the peace, Lawrence wrote back to Darrow, somewhat denying this account, saying that it was maybe only ten minutes of discussion. Lawrence, in this later account, credits Oppenheimer as being the hardest pusher for the argument that unless the demonstration took out a city, it wouldn’t be compelling. I’m not sure I completely believe Lawrence’s later recant, both because Darrow seemed awfully convinced of his recollection and because so much changed on how the bomb was perceived after the Japanese surrendered, but it is all an interesting hint as some of the subtleties of this disagreement that get lost from the final documents alone. In any case, I don’t know which is more problematic: that they debated for an hour and after all that, concluded it was necessary, or that they spent no more than ten minutes on the question.2

1945-08-10 - Groves memo on next bombs

As an aside, one question that sometimes gets brought up at this point in the conversation is, well, didn’t they only have two bombs to use? So wouldn’t a demonstration have meant that they would have only had another bomb left, perhaps not enough? This is only an issue if you consider the timescale to be as it was played out — e.g., using both bombs as soon as possible, in early August. A third plutonium bomb would have been ready by August 17th or 18th (they originally thought the 24th, but it got pushed up), so one could imagine a situation in which things were delayed by a week or so and there would have been no real difference even if one bomb was expended on a demonstration. If they had been willing to wait a few more weeks, they could have turned the Little Boy bomb’s fuel into several “composite” core implosion bombs, as Oppenheimer had suggested to Groves after Trinity. I only bring the above up because people sometimes get confused about their weapon availability and the timing issue. They made choices on this that constrained their options. They had reasons for doing it, but it was not as if the way things happened was set in stone. (The invasion of Japan was not scheduled until November 1st.)3

So, obviously, they didn’t choose to demonstrate the bomb first. But what if they had? I find this an interesting counterfactual to ponder. Would dropping the bomb in Tokyo Bay have been militarily feasible? I suspect so. If they could drop the bombs on cities, they could probably drop them near cities. To put it another way: I have faith they could have figured out a way to do it operationally, because they were clever people.4

But would it have caused the Japanese high command to surrender? Personally, I doubt it. Why? Because it’s not even clear that the actual atomic bombings were what caused the Japanese high command to surrender. There is a strong argument that it was the Soviet invasion of Manchuria that “shocked” them into their final capitulation. I don’t know if I completely buy that argument (this is the subject of a future blog post), but I am convinced that the Soviet invasion was very important and disturbing to the Japanese with regards to their long-term political visions for the country. If an atomic bomb dropped on an actual city was not, by itself, entirely enough, what good would seeing a bomb detonated without destruction do? One cannot know, but I suspect it would not have done the trick.

The maximum size of a 20 kiloton mushroom cloud in Tokyo Bay, as viewed from the roof of the Imperial Palace today, as visualized by NUKEMAP3D. Firebombed Tokyo of 1945 would have afforded a less skyscraper-cluttered view, obviously.

The maximum size of the mushroom cloud of a 20 kiloton nuclear detonation in Tokyo Bay, as viewed from the roof of the Imperial Palace today, as visualized by NUKEMAP3D. Firebombed Tokyo of 1945 would have afforded a less skyscraper-cluttered view, obviously.

Of course, the Chicago scientists suspected that as well, but said it was necessary from a moral point of view. Sure, the Japanese might not surrender, but then, at least, you can say you showed them what was coming first.  As it was, we gave no real warning whatsoever before dropping it on Hiroshima. But here’s the question I come to next: could you demonstrate it, and then drop it on a city? That is, could the United States really say: “we have made this apocalyptic weapon, unleashed the atom, and many other peril/hope clichés — and we have chosen not to use it to take life… yet. But if you don’t give in to our demands, we will unleash it on your people.” How could that not look like pure blackmail, pure terrorism? Could they then turn around and start killing people by the tens of thousands, having announced their capability to do so? Somehow I suspect the public relations angle would be almost impossible. By demonstrating it first, they would be implying that they knew that it was perhaps not just another weapon, not just another way to wage war. And that acknowledgment would mean that they would definitely be seen as crossing a line if they then went on to use it.

As it was, that line, between the bomb as “just another weapon” and something “special,” was negotiated over time. I think the demonstration option was, for this reason, never really going to be on the table: it would have forced the American policymakers to come to terms with whether the atomic bomb was a weapon suitable for warfare on an earlier schedule than they were prepared to. As it was, their imagery, language, and deliberations are full of ambiguity on this. Sometimes they thought it would have new implications for “man’s position in the universe” (and other “special bomb” notions), sometimes they thought it was just an expedient form of firebombing with extra propaganda value because it would be very bright and colorful. Secrecy enabled them to hedge their bets on this question, for better or worse.

Without imagery like this, would the world fear nuclear weapons more, or less?

Without imagery like this, would the world fear nuclear weapons more, or less? When, if ever, would the first use of nuclear weapons in warfare have been?

So who was right? I don’t know. We can’t replay history to see what happened, obviously. I think the idea of a demonstration is an interesting expression of a certain type of ethical ideal, though it went so far against the practical desires of the military and political figures that it is hard to imagine any way it would have been pursued. I am not sure it would even have been successful, or resolved the moral bind of the atomic bomb.

I do find myself somewhat agreeing with those scientists who said that perhaps it was better to draw blood with the smaller, cruder bombs, before the really big ones came around — and they knew those were coming. If we didn’t have Hiroshima and Nagasaki, what would we point to, to talk about why not to use nuclear weapons? Would people think the bombs were not that impressive, or even more impressive than they were? I don’t know, but there is something to the notion that knowing the gritty, gruesome reality (and its limitations) is better than not. It took the Holocaust for the world to (mostly) renounce genocide, maybe it took Hiroshima and Nagasaki for the nuclear taboo to be established (arguably). That, perhaps, is the most hopeful argument here, the one that sees Hiroshima and Nagasaki as not just the first cities to be atomic bombed, but the last, but I am sure this is little solace to the people who were in those cities at the time.

Notes
  1. This was part of a larger set of recommendations these scientists made, including those which touched on the “Super” bomb, future governance of the atom, and other topics of great interest. Report of the Scientific Panel of the Interim Committee (16 June 1945), Harrison-Bundy Files Relating to the Development of the Atomic Bomb, 1942-1946, microfilm publication M1108 (Washington, D.C.: National Archives and Records Administration, 1980), Roll 6, Target 5, Folder 76, “Interim Comittee — Scientific Panel.” []
  2. Karl Darrow to Ernest Lawrence (9 August 1945), copy in Nuclear Testing Archive, NV0724362 [note the NTA has the wrong name and date on this in their database]; Ernest Lawrence to Karl Darrow (17 August 1945), copy in Nuclear Testing Archive,NV0724363. []
  3. On the composite core question, see J. Robert Oppenheimer to Leslie Groves (19 July 1945), copy in Nuclear Testing Archive, NV0311426; Leslie Groves to J. Robert Oppenheimer (19 July 1945), Correspondence (“Top Secret”) of the Manhattan Engineer District, Roll 1, Target 6, Folder 5B: “Directives, Memorandums, etc to and from Chief of Staff, Secretary of War, etc.” []
  4. To answer one other question that comes up: would such a demonstration create deadly fallout? Not if it was set to detonate high in the air, like at Hiroshima and Nagasaki. If it was detonated underwater the fallout would be mostly limited to the area around the bomb detonation itself. It would be hard to actually create a lot of fallout with a bomb detonated over water and not land, in any case. “Local fallout,” the acutely deadly kind, is caused in part by the mixing of heavier dirt and debris with the radioactive fireball, which causes the fission products to descend very rapidly, while they are still very “hot.” []
Redactions

The Fat Man’s uranium

Monday, November 10th, 2014

What a long set of weeks it has been! On top of my usual teaching load (a few hours of lecture per week, grading, etc.), I have given two public talks and then flown to Chicago and back for the annual History of Science Society meeting. So I’ve gotten behind on the blog posting, though I have more content than usual for the next few weeks built up in my drafts folder, without time for me to finish it up. During this busy time, by complete coincidence, I also got briefly interviewed for both The Atlantic (on plutonium and nuclear waste) and The New York Times (on the apparent virality of nuclear weapons history).

Louis Slotin and Herb Lehr at the assembly of the Trinity "Gadget." Source: Los Alamos National Laboratory Archives, photo TR-229.

Louis Slotin and Herb Lehr at the assembly of the Trinity “Gadget.” Source: Los Alamos National Laboratory Archives, photo TR-229.

The Times article had a phrase in it that has generated a few e-mails to me from a confused reader, so I thought it was worth clarifying on here, because it is actually an interesting detail. It is one of those funny phrases that if you knew nothing about the bomb you’d never notice it, and if you knew a good deal about the bomb you’d think it was wrong, but if you know a whole lot more than most people care to know unless they are serious bomb nerds you actually see that it is correct.

Here’s the quote:

First, he glanced at the scientists assembling what they called “the gadget,” a spherical test device five feet in diameter. Then, atop a wooden crate nearby, he noticed a small, blocky object, nondescript except for the role he suddenly realized it played: It was a uranium slug that held the bomb’s fuel. In July 1945, its detonation lit up the New Mexican desert and sent out shock waves that begot a new era.

I’ve added emphasis to the part that may seem confusing. The Trinity “Gadget” and the Fat Man bomb, as everyone knows, were fueled by fission reactions in a sphere of plutonium. The Little Boy bomb dropped on Hiroshima, by contrast, was fueled by enriched uranium. So what’s this reference to a uranium slug inside the Trinity Gadget? Isn’t that wrong?

Detail from the above photo showing the tamper plug cylinder. Inset is a rare glimpse of what the tamper probably looked like, taken from a different Los Alamos photo related to Slotin's criticality accident. (It is in the middle-right of the linked photo. Yes, I cop to spending time searching the edges of photos like this for interesting things...) You can see how the tamper plug, rotated, would be inserted into the middle of the tamper sphere.

Detail from the above photo showing the tamper plug cylinder. Inset is a rare glimpse of what the tamper probably looked like, taken from a different Los Alamos photo related to Slotin’s criticality accident. (It is in the middle-right of the linked photo. Yes, I cop to spending time searching the edges of photos like this…) You can see how the tamper plug, rotated, would be inserted into the middle of the tamper sphere.

Perhaps surprisingly — no, it’s not. There was uranium inside both the “Gadget” and Fat Man devices — in the tamper. The tamper was a sphere of uranium that encased the plutonium pit, which itself encased a polonium-beryllium neutron source, Russian-doll style. Here uranium was chosen primarily for its physical rather than its nuclear properties: it was naturalunenriched uranium (“Tuballoy,” in the security jargon of the time), and its purpose was to hold together the core while the core did its best to try and explode. (It also helped reflect neutrons back into the core, which also worked to improve the efficiency.)

The inside of an exploding fission bomb can be considered as a race between two different processes. One is the fission reaction itself, which, as it progresses, rapidly heats the core. This heating of the core, however, causes the core to rapidly expand — the core is trying to blow itself apart. If the core expands beyond a certain radius, the fission chain reaction stops, because the fission neutrons won’t find further plutonium nuclei to react with. If you are a bomb designer, and want your bomb to have a pretty big boom, you want to hold the bomb core together as long as possible, because every 10 nanoseconds or so you can hold it together equals another generation of fission reactions, and each generation releases exponentially more energy than the previous.1

An image that somewhat evokes how bomb designers talk about the dueling conditions inside of the bomb, when they are talking to each other. The "snowplow region" is where the expanding bomb core runs into the tamper and is compressing it from the inside. This is a level of bomb design that I would have normally assumed would be classified but it has been very clearly declassified here, so I guess not. From Glasstone, "Weapons Activities of Los Alamos, Part I" (see footnotes).

An image that somewhat evokes how bomb designers talk about the dueling conditions inside of the bomb, when they are talking to each other. The “snowplow region” is where the expanding bomb core runs into the tamper and is compressing it from the inside. This is a level of bomb design that I would have normally assumed would be classified but it has been very clearly declassified here, so I guess not. From Glasstone, “Weapons Activities of Los Alamos, Part I” (see footnotes).

So in the Fat Man and Trinity bombs, this is accomplished with a heavy sphere of natural uranium metal. Uranium is heavy and dense, and the process of making plutonium and enriched uranium required the United States to stockpile thousands of tons of it, so the relatively small amount needed for a tamper was easily at-hand. It makes a good substance with which to try and hold an exploding atomic bomb together. The Little Boy bomb, as an aside, used a tungsten tamper, for some reason (maybe to avoid excessive background neutrons, I don’t know).

Now to add one more little bit of detail: we tend to think of the Trinity/Fat Man implosion bombs as just being a set of spheres-inside-spheres. This is a convenient simplification of the actual geometry, which had other factors that influenced it. The tamper, for example, was not just two halves of a hollow sphere that could fit together. Rather, it was more like a solid sphere out of which a central cylinder had been removed. The cylinder was known as the “tamper plug,” and was itself made of two halves that, when assembled, had room for the plutonium pit inside of them.

Why do it this way? Because the scientists and engineers wanted to be able to insert the fissile pit portion into the bomb as one of the final additions. This makes good sense from a safety point of view — they wanted it to be relatively easy to add the final, “nuclear” component of the bomb and to keep it separate from the non-nuclear components (like the high explosives) as long as possible. I don’t want to over-emphasize the “ease” of this operation, because it was not a quick, last-minute action to put the pit inside the bomb. (Some later bomb designs which featured in-flight core insertion were designed to be just this, but this was some years away.) It was still a tetchy, careful operation. But they could assemble the entire rest of the tamper, pusher, and high explosives, then remove one layer of high explosives, remove the top of the pusher, and then lower the tamper plug (with pit) into the center, then replace all of the other parts, hook up the detonators and electrical system, and so on.

A rendering I made in Blender to illustrate the principle here. The pit and initiator are inside of the plug (expanded at right), which is then sealed into a cylinder and inserted into the tamper sphere at the center of the bomb. The tamper is itself embedded in a boron shell which is inside of an aluminum shell which is inside of the explosive lenses which is inside of the casing. This is part of a modeling/visualizing project I've been working on for a little while now and will post more on at a future date. 

A rendering I made in Blender to illustrate the principle here. The pit and initiator are inside of the plug (expanded at right), which is then sealed into a cylinder and inserted into the tamper sphere at the center of the bomb. The tamper is itself embedded in a boron shell which is inside of an aluminum shell which is inside of the explosive lenses which is inside of the casing. This is part of a modeling/visualizing project I’ve been working on for a little while now and will post more on at a future date. The dimensions are roughly correct though there are still many simplified detail (e.g. exactly how the plug fits together — there were uranium screws!).

So when John Coster-Mullen describes, as in the previously-quoted New York Times article, finding a picture of the tamper plug, it’s kind of a cool thing. There’s only one picture that shows it (the one at the beginning of this post), and it is one of those things that you don’t even usually notice about that picture until someone points it out to you. I never noticed it until John pointed it out for me, even though I’d seen the picture many times before. Usually one’s attention is drawn to the Gadget sphere itself, and the people standing around (including Louis Slotin, who would later be killed by playing with a core). It’s kind of surprising it was declassified, since the length of the tamper plug is the diameter of the tamper, and the width of the plug is just a little bigger than the diameter of the plutonium core. The US government usually doesn’t like to reveal, even inadvertently, those kinds of numbers.

There is also one little fact about the natural uranium in the Gadget and Fat Man bomb that is not well appreciated, and I didn’t appreciate well until reading John’s book. (Which I have heard people say is rather expensive for a self-published production, but if you’re a serious Manhattan Project geek it is hard to imagine how you’d get by without a copy of it — it is dense with technical details and anecdotes. It is one of the only books that I don’t often bother to put back in the bookcase because I end up needing to reference it every week or so.)

Neutron cross-sections for the fissioning of uranium and plutonium. The higher the cross-section, the more likely that fission will occur. (Not shown on here is the competing capture cross-section, which matters a lot for U-238.) The indicated "fission neutron energy" means that that is the approximate energy level of neutrons released from fission reactions. So you can see why, in a reactor, those are slowed down by the moderator to increase the likelihood of fissioning. In a bomb, there is no time for slowing things down, so you need much more fissile material in much higher concentrations. Source: World Nuclear  Association.

Neutron cross-sections for the fissioning of uranium and plutonium. The higher the cross-section, the more likely that fission will occur. The indicated “fission neutron energy” means that that is the approximate energy level of neutrons released from fission reactions. So you can see why, in a reactor, those are slowed down by the moderator to increase the likelihood of fissioning. In a bomb, there is no time for slowing things down, so you need fissile material in much higher concentrations. Source: World Nuclear Association.

In talking about which elements are fissile — that is, can sustain a nuclear fission chain reaction — technical people tend to talk about neutron cross sections. This just means, in essence, that the likelihood of a giving elemental isotope (e.g. uranium-235, plutonium-239) undergoing fission when encountering a neutron is related to the energy of that neutron. At the size of neutrons, energy, speed, and temperature all considered to be the same thing. If you look at a neutron cross section chart, like the one above, you will see that uranium-235 has a high likelihood of fissioning from slow neutrons, and a low-but-not-zero likelihood of fissioning from faster neutrons. You will also see that the neutrons released by fission reactions are pretty fast. This is why to sustain a chain reaction in uranium you either need to slow the neutrons down (like in a nuclear reactor, which uses a moderator to do this), or pack in so many U-235 atoms that even the low probability of fissioning from fast neutrons doesn’t mean that a chain reaction won’t happen (like in a nuclear bomb, where you enrich the uranium to be mostly U-235).

Still with me? If you look a little further on the graph, you’ll see that uranium-238 also has a possibility of fissioning, but it is a pretty low one and only even becomes possible with pretty fast neutrons. This is why, in a nutshell, that unenriched uranium can’t power an atomic bomb by itself: it is fissionable but not fissile, because it can’t reliably take fission neutrons and turn them into further fission reactions. But people who have studied how thermonuclear weapons are used know that even uranium-238 can contribute a lot of explosive energy, if it is in the presence of a lot of high-energy neutrons. In a multistage hydrogen bomb, at least 50% of the final explosive energy is derived from the fissioning of U-238, which is made possible by the high-energy neutrons produced from the nuclear fusion stage of the bomb (which itself is set off by an initial fission stage). The neutrons produced by deuterium-tritium fusion are around 14 times more energetic than fission neutrons, so that lets them fission U-238 easily. From the cross-section chart above, you can see that U-238 fissioning can happen from fission neutrons, but only if they happen to be pretty high energy to begin with and stay that way. In practice, neutrons lose energy rather quickly. Still, according to a rather sophisticated analysis of the glassified remains of the Trinity test (“Trinitite”) done a few years back by the scientistsThomas M. Semkow, Pravin P. Parekh, and Douglas K. Haines, a significant portion of the final fissioning output at Trinity (and presumably also Nagasaki) came from the fast fissioning of the tamper, with some of that energy released from the U-238 fissioning.2

For the hardcore bomb geeks, here is a sort of "conclusion table" from the Semkow et al. article. Note that they calculate at least 30% fissioning from uranium, and give some indication the amount of compression of the core, the number of neutrons created, and so on.

For the hardcore bomb geeks, here is a sort of “conclusion table” from the Semkow et al. article. Note that they calculate at least 30% fissioning from uranium, and give some indication the amount of compression of the core, the number of neutrons created, and so on. Their terminology of the “eyeball” is taken from Richard Rhodes, who uses the term in passing in The Making of the Atomic Bomb, and refers to the confined area where the fission chain reaction is taking place.

How significant? Semkow et al. calculate that about 30% of the total yield of the Trinity test came from fissioning of the uranium tamper, which translates to about 6 kilotons of energy. If they had made the tamper out of tungsten (as was the Little Boy tamper), then the total yield of the Gadget would have only been around 14-15 kilotons — not that different from Little Boy (which was ~13-15 kt). And presumably if the Little Boy bomb had used a uranium tamper, assuming that didn’t cause problems with the design (which it probably would have, otherwise they probably would have used one), it would have had the same yield. (This doesn’t mean that Little Boy wasn’t, in fact, horribly inefficient — it got about the same yield but it required 10X the fissile the material to do so!) The total mass of the tamper was around 120 kg of natural uranium, so if it contributed 6 kilotons of yield that means around 350 grams of the tamper underwent fission, and that is about 0.3% of the total mass.3

So the fact that Trinity and Fat Man had uranium inside of them is already kind of interesting, but the fact that a large portion of the blast derived from that uranium is sort of a neat detail. Why don’t we generally learn about this? It isn’t that it is so terribly classified, per se, but it does require a lot of detailed explanation, as evidenced by the length of this post. We tend to abstract the mechanics of the bombs for explaining their conceptual role, and explaining the basic concepts of how they work. I have no problem with this, personally, because hey, let’s be honest, the exact amount of energy derived from different types of fissioning in the bombs is a pretty wonky thing to care about! But every once in awhile you need to understand the wonky things if you want to talk about, say, what that funny little “plug” is in the top-most photograph, and its role in the bomb. I suppose one of the points of the phenomena described by the Times article, where the geek population on the Internet is providing a newfound audience to Manhattan Project details, is that these sorts of wonky aspects are no longer limited to people like John Coster-Mullen, Carey Sublette, or myself. There are some people who might see this focusing on the technical details as missing the broader picture. I don’t happen to think that myself — much of the broader picture is in fact embedded in the technical details, and “new” discussions of technical details are one way of shaking people out of the calcified narratives of the Manhattan Project, something which, as we approach the 70th anniversary of Hiroshima and Nagasaki, seems to me a valuable endeavor.

Notes
  1. Calculating the efficiency of the bomb as a function of how well you can hold it together is apparently the essence of the still mostly-classified Bethe-Feynman formula. It is described qualitatively in Samuel Glasstone, “Weapons Activities of Los Alamos Scientific Laboratory, Part I,” LA-1632 (January 1954), 34-37. My copy of this report comes from the NNSA’s FOIA Reading Room. I downloaded the file in 2009, and sometime since then all of their PDFs have gotten corrupted somehow, and so many of the pages of the PDFs now available on their site are unreadable. For those who are curious, at a technical level, the corruption involved a systematic stripping out of the carriage return (0D) ASCII characters from the PDFs — there are none in any of the files, and there should be several thousand of them. Here is a screenshot from a hex editor showing the corrupted file (on left) versus the uncorrupted one (on the right). There seems to be no easy fix for this problem. I have tried to contact the NNSA about this but have gotten no response. It is one of many troubling incidents revealing, in my view, the very low priority that public release of information, and poor understanding of public-facing information technology, with regards to the present nuclear agencies. []
  2. Thomas M. Semkow, Pravin P. Parekh, and Douglas K. Haines, “Modeling the Effects of the Trinity Test,” Applied Modeling and Computations in Nuclear Science, ACS Symposium Series (American Chemical Society: Washington, DC, 2006), 142-159. The authors do not estimate the amount of tamper energy to have been released from U-238 fissioning as opposed to U-235 fissioning. []
  3. A 120 kg tamper of natural uranium ought to contain around 840 grams of U-235 in it, as an aside, which if that all fissioned at once would release around 14 kilotons of energy. The rule of thumb for uranium is that every kilogram which fissions releases about 17 kilotons. []
Meditations

Tokyo vs. Hiroshima

Monday, September 22nd, 2014

How many people would have died if an atomic bomb had been dropped on Tokyo in early 1945, instead of firebombs? Before you accuse me of excessive obsession with morbidity (as one anonymous e-mailer recently did), let me explain to you how I came to ask myself this question, and what the consequences of the answer are.

Before the dropping of the atomic bomb on Hiroshima and Nagasaki, there was the burning of Tokyo. Operation Meetinghouse, the early March 1945 raid on Tokyo that involved over 330 B-29s dropping incendiary bombs from low-altitude at night, killed roughly 100,000 people, and may have injured and made homeless an order of magnitude more. As with all statistics on the damage caused by strategic bombing during World War II, there are debatable points and methodologies, but most people accept that the bombing of Tokyo probably had at least as many deaths as the Hiroshima bombing raid, and probably more. It is sometimes listed as the most single deadly air raid of all time as a consequence.

The ruins of 1945: Tokyo, left, and Hiroshima, right.

The ruins of 1945: Tokyo, left, and Hiroshima, right.

So it is understandable that many people, including myself, point to Tokyo whenever people want to talk about Hiroshima and Nagasaki. You can’t see the atomic bombings in isolation. The practice of targeting civilian areas with massively destructive aerial bombing had already been done before. And to some, the atomic bombs were just a refinement of the art of area bombing — a more efficient means to accomplish the same ends.1

However, there are a few points that I fear get missed in that kind of equivalence. I certainly agree that the philosophy of bombing used at Hiroshima and Nagasaki wasn’t a new one. Indeed, the experience of firebombing gave a lot of guidance to the question of nuclear targeting. The goals were similar, though the people planning the atomic bombs emphasized the raw terror that they hoped such a spectacle would inspire.

But I depart from the standard comparison in two places. The first is the idea that since the atomic bombings were not original in targeting civilians, then they do not present a moral or ethical question. As I’ve written about before, I think the question of morality gets more problematic. If the atomic bombings were one-off events, rare interventions to end the war, then it might (for some) be compelling to say that they were worth the price of crossing over some kind of line regarding the deliberate burning of civilians to death en masse. But if they were instead the continuation of a well-established policy of burning civilians to death en masse, then the moral question gets much broader. The question changes from, Was it morally justified to commit a civilian massacre two times?, to Was it morally justified to make civilian massacre a standard means of fighting the war? 

I want to state explicitly that I don’t think, and I don’t want my phrasing to imply, that the answer to the above is necessarily an unequivocal “no.” There are certainly many moral frameworks that can allow for massacres (e.g. ends-justify-the-means). But I prefer to not dress this sort of thing up in euphemisms, whether we think it justified or not.  Massacre means to deliberately and indiscriminately kill people. That is what you get when you bomb densely-populated cities with weapons that cannot distinguish between civilians and members of the military. Incendiary raids and atomic bombs certainly fall in this category, whether one thinks that the circumstances required them or not.

Japanese cities destroyed by strategic bombing in World War II. More information about this map here.

Japanese cities destroyed by strategic bombing in World War II. More information about this map here.

The second place I depart is a technical one. There are several important differences between the effects of firebombing and atomic bombing. They are not, even in the case of the bombing of Japan, strictly equivalent from the point of view of their effects or their outcomes.

The Tokyo firebombing raid was a relatively slow (compared to an atomic bomb), massively-distributed attack. The Tokyo raid involved hundreds of B-29 bombers arriving and attacking over the course of several hours. Such massive groups of B-29s could be heard and tracked from a considerable distance. They spread their bombs over a large area of the city, with the goal of creating a mass conflagration that would be impossible to control. They could be fought against with interceptors and anti-aircraft guns; air-raid alarms could be sounded; civilians could flee to shelter, or outside of the city itself.  This is not to imply that any of these strategies were necessarily effective, and it does not necessarily make firebombing raids any more “humane.” But it does change the outcome quite a bit, when compared to an atomic bomb attack.

The atomic bombing raids of Hiroshima and Nagasaki were fast, near-instantaneous attacks. They involved a single B-29 weather plane in advance, and then two or three B-29s approaching the city, one with the bomb itself. This means that effective air-raid warning was minimal, because it was not possible to distinguish an atomic bomb attack from a reconnaissance or weather flight, all of which were common by that late stage in the war. (And obviously any hope of detecting an atomic bomb attack was impossible prior to Hiroshima.)

Drawing by Goro Kiyoyoshi of his memories of the Hiroshima attack. "I got on a streetcar of the Kabe line about 8:10 AM. The door was open and I was standing there. As I heard the starting bell ring, I saw a silver flash and heard an explosion over the platform on which l had just walked. Next moment everything went dark. Instinctively I jumped down to the track and braced myself against it. Putting a handkerchief to my mouth, I covered my eyes and ears with my hands."

Drawing by Goro Kiyoyoshi of his memories of the Hiroshima attack. “I got on a streetcar of the Kabe line about 8:10 AM. The door was open and I was standing there. As I heard the starting bell ring, I saw a silver flash and heard an explosion over the platform on which l had just walked. Next moment everything went dark. Instinctively I jumped down to the track and braced myself against it. Putting a handkerchief to my mouth, I covered my eyes and ears with my hands.” From Unforgettable Fire: Drawings by Atomic Bomb Survivors (1977).

The primary acute effects of the atomic bombs were blast and thermal radiation. The former travels at the speed of sound, the latter significantly faster. (The rays are transmitted at more or less the speed of light, but the intensity and duration of the thermal pulse is a more complex phenomena and unfolds over the course of several seconds.) The blast knocks down buildings. The thermal radiation heats and burns. Both contribute to the starting of fires — the thermal radiation directly (for certain materials), the blast wave indirectly by knocking over flammable materials, stoves, candles, etc. After Hiroshima there was a significant firestorm, as with incendiary bombing, but there was not after Nagasaki. There was no effective preparation for such an attack — perhaps if they had the foresight of some later Civil Defense techniques, some lives could have been saved (different shelter types did affect the fatality rates significantly, even close in to the zero point), but obviously this was not quite in the cards during the war itself, when the atomic bomb was such a novelty. There was no time for shelters, no time to flee the city, no time even for real comprehension of what was happening — a bright light followed by a crushing blast, followed by fire. For those who survived the blast and fire, there were radiation effects, if they were with a few kilometers of the epicenter. This could range from acute radiation sickness and death with several weeks, to an increased cancer risk over the course of their lives.

Are the atomic bomb effects significantly different from firebombing to warrant putting them into different ethical or moral categories? One could argue the point either way. I tend to think that they are both pretty terrible forms of suffering, but they are not identical. In many ways the atomic bombing effects were significantly worse for the people living in the target cities — all of the suffering of firebombing accelerated, with a few new terrors added into the mix, and with less warning.

Table from a 1963 Office of Civil Defense report, "Survey of the Thermal Threat of Nuclear Weapons," by Jack C. Rogers and T. Miller. These numbers are not necessarily authoritative, but they give some indication of the relative mortality rates differences I am talking about.

Table from a 1963 Office of Civil Defense report, “Survey of the Thermal Threat of Nuclear Weapons,” by Jack C. Rogers and T. Miller. These numbers are not necessarily authoritative, but lay out the situation well: atomic bombs have much higher mortality and casualty rates per square mile than firebombing, but destroy proportionally smaller amounts of area.

But the equivalence argument also misses some important differences in how deadly the atomic bombs were. The firebombing of Tokyo did, indeed, kill the most people of any air raid in history — from 80,000 to over 100,000 dead in a single raid. But the city of Tokyo had some 5 million people living in it. In the areas targeted, there were 1.5 million people living. So that means that it killed no more than 2% of the total population of the city, and no more than 7% of the people who lived in the targeted areas. The bombing of Hiroshima killed between 90,000 and 160,000 people in a city of 345,000 or so. So that is a fatality rate of 26-46%, depending on whose fatality estimates you go with. The bombing of Nagasaki killed between 39,000 to 80,000 people in a city of 260,000 people or so. So that is a fatality rate of 15-30%.

So to put it another way, the Hiroshima bombing was around 5 times more deadly than the Tokyo raid per capita, and the Nagasaki bombing was maybe 4 times more deadly. The total number dead is similar in all three cases, but the total number of people possible to kill in Tokyo was much higher than the number of people in Hiroshima and Nagasaki.

This isn’t the whole story, though. There is a subtle technical difference mixed in here. Firebombing on par with the Tokyo raid spread a moderate chance of death over a large area. The atomic bombs dropped in World War II spread a very high chance of death over a relatively small area. So depending on the target in question, the difference in fatalities might or might not matter. The Hiroshima bomb was perfectly capable of killing something like half of the city — but it was a pretty small city, compared to Tokyo. Tokyo has areas of incredibly high density, but also large areas of relatively moderate to low density.

So why does this matter? From an ethical standpoint, I’m not sure it does. The targeting of civilians for mass destruction seems to be the core ethical issue, whether you do this by means of fire, neutrons, or toxic gas. But I do think we end up underestimating the effects of the atomic bombs if we see them as exactly equivalent to firebombs. There is an error in seeing the atomic bombs as just an expeditious form of firebombing — it both overstates the deadliness of firebombing while understating the deadliness of atomic bombs.

This map gives a rough indication of the methodology used to construct the casualty estimates for a Little Boy bomb targeted on World War II Tokyo. Percentages are expected average fatality rates. The actual method used (see below) used many more gradations of difference. One can see, though, the way in which the most intense of the effects of the atomic bomb are highly localized relative to the total size of Tokyo.

This map gives a rough indication of the methodology used to construct the casualty estimates for a Little Boy bomb targeted on World War II Tokyo. Percentages are expected average fatality rates. The actual method used (see below) used many more gradations of difference. One can see, though, the way in which the most intense of the effects of the atomic bomb are highly localized relative to the total size of Tokyo. The underlying population density map of Tokyo comes from the very useful Japanairraids.org.

All of this is what led me to the question I opened with: What if, in some hypothetical alternative universe, instead of launching a firebombing raid in early March 1945, the US was able to drop the Little Boy atomic bomb onto Tokyo? What would the casualties have been for that raid?

Obviously an exact answer is not possible. But we do have population density maps of Tokyo, and we do have records on the relationship between distance from “ground zero” and percentage of population killed. There are lots of uncertainties, here, regarding the types of buildings, the differences in geography, and other things that are hard to estimate. But let’s do a rough estimation.

If we transpose the effects of Hiroshima — a 15 kiloton bomb detonated around 1,968 feet above the ground — to the population densities of Tokyo, what is the result? I don’t want to clog up the blog post with a detailed explanation of the methodology I’ve used, so I’m putting it at the end with the footnotes. The basic gist of it was this: I took a population density map of Tokyo from 1940, divided the different density areas into different layers in Photoshop, then selected radii based on bomb effects and did pixel counting. I used all of this to come up with rough minimum-maximum estimates of how many people lived in areas at different regions from the bomb blast, and then multiplied those population counts against known average fatality/casualty rate data taken from Hiroshima.

I looked at two ground zeros, to further emphasize the intense locality of a Hiroshima-sized atomic bomb attack (compared to a firebombing raid). If targeted on the moderately-dense Honjo area (which is more or less the center of the firebombing attack), one could roughly expect there to be between 213,000 and 344,000 fatalities, and between 442,000 and 686,000 injuries. This is the ground zero shown in the above image. If you move it north-west by only 1 km, though, to the more densely populated Asakusa area, the numbers change to 267,000 to 381,000 dead and 459,000 to 753,000 injured.

So if the Hiroshima bomb had been dropped on Tokyo, it probably would have destroyed less area than the March 1945 Tokyo firebombings — something like 5 square miles, compared to the 15 square miles destroyed by firebombing. However it would have killed between two and four times as many people who died in the firebombings, and injured possibly fewer or the same amount of people.

These numbers seem roughly plausible to me, even given all of the uncertainties involved, and they align with the rough guess one would make from the relative area destruction and casualty rates cited earlier. It is of note that the shifting of an atomic bomb’s aiming point can increase total casualties by several tens of thousands of people in a city the density of Tokyo; firebombing is probably not quite as dependent on any given aiming point, given how much lower the accuracy was.

Finally, it is worth noting that the Tokyo firebombing was much more fatal than most of the other firebombing raids. As the first low-altitude, massed night B-29 incendiary raid, against Japan’s highest-density city, it was especially fatal. Later raids killed, on average, orders of magnitudes less, both for the reasons given at the beginning (e.g. fleeing when you hear hundreds of B-29s in the distance), and because of much lower population densities. Had Hiroshima been firebombed, the fatalities would have certainly been much lower than the atomic bombings, because the Tokyo case is in fact an anomalously high one.

Atomic bombings may be ethically no better or worse than firebombing raids like Tokyo, but to regard them as simply an expedient form of firebombing misses a key point about their relative deadliness: If you have to pick, and you get to pick, one should choose to be firebombed, not atomic bombed — unless you know exactly where the bombs are going to go off.

Click for the full casualty calculation methodology.

Notes
  1. On this, see esp. Michael Gordin’s Five Days in August, and, perhaps,  my review of it. []