Posts Tagged ‘Nagasaki’

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. []
Meditations

The luck of Kokura

Friday, August 22nd, 2014

On the morning of August 9th, 1945, a B-29 bomber left the island of Tinian intending to drop an atomic bomb on the city of Kokura, the location of one of the largest arsenals still standing in Japan. On arriving at the target, the plane found it obscured by clouds. It turned south and went to its secondary target: Nagasaki. 

Supposedly, some in Japan still refer to the “luck of Kokura” in reference to this time in which some bad weather saved the lives of tens of thousands of people there. But what really happened that morning? Was it bad weather, or something else, that obscured, and thus saved, Kokura? 

Surprisingly, there are actually a few different theories floating around, and the uncertainty over the matter is generally not realized or acknowledged.

Model of the Kokura arsenal made for targeting purposes, ca. 1945. North is in the lower-right hand corner. Source: USAAF photos, via Fold3.com.

Model of the Kokura arsenal made for targeting purposes, ca. 1945. North is in the lower-right hand corner. Source: USAAF photos, via Fold3.com.

But first, let’s review the basics of the mission. The Kokura/Nagasaki mission (dubbed CENTERBOARD II), as with the Hiroshima mission before it (CENTERBOARD I), did not involve the bomber flying on its lonesome to the target, as is sometimes imagined. There were a total of six planes involved in the mission, all B-29 bombers. One of them was the strike plane that carried the Fat Man implosion bomb (Bockscar).1  Two other planes (The Great Artiste and Big Stink) were instrument and observation planes. One other plane was a “standby” plane (Full House) that was to serve as backup if the three bombing planes ran into air resistance — because they didn’t, it instead flew back to Iwo Jima instead of on to the target after a rendezvous with the bombing plane. Lastly, there were two weather planes that flew out in advance, one to Nagasaki (the Laggin’ Dragon), the other to Kokura (the Enola Gay, the same plane that had dropped the atomic bomb on Hiroshima a few days earlier, but with a different crew). The weather planes would check out bombing conditions and then circle back, helping the bomber plane determine whether the primary or secondary target would be used. Niigata, a third atomic bombing target, was not considered on this mission because of its great geographical distance from Kokura and Nagasaki.

Bockscar was being piloted by Major Charles Sweeney. It had taken off from the island of Tinian at 3:47am, Tinian time. They had arrived at a rendezvous point at Yakushima Island around 9:15am. It rendezvoused with one of the other B-29s (the instrument plane), but did not spot the other one (the photo plane). At 9:50am, the pilot of Bockscar, Charles Sweeney, gave up and continued on to Kokura, having waited some 30 minutes longer than he was supposed to. At 10:44am, they arrived at Kokura. The flight log records that “Target was obscured by heavy ground haze and smoke.” A crew member of Bockscar rated it as “7/10 clouds coverage – Bomb must be dropped visually but I don’t think our chances are very good.”2

Three bombing runs on Kokura were attempted, but “at no time was the aiming point seen,” as the flight log recorded. Visual bombing had been made a mandatory requirement (they did not trust the accuracy of radar-assisted bombing), so this made Kokura a failed mission. Since Bockscar had limited fuel, Sweeney decided to continue on to the secondary target, Nagasaki. They arrived at Nagasaki at 11:50am, which they also found obscured by smoke and clouds, to the degree that they made the target approach entirely by radar. Right at the last possible moment, the clouds parted just enough for the bombardier to site the target and drop the bomb. (It missed the intended target by a significant margin.) Bockscar circled the target once and then, at 12:05pm, took off for Okinawa, and from there, after refueling, Tinian.

Care about the details of the Hiroshima and Nagasaki bombings? Get this book.

Care about the details of the Hiroshima and Nagasaki bombings? Get John’s book. I’m not just saying that because he says nice things about my blog, either.

An aside: For anyone interested in the nitty-gritty details of the Hiroshima and Nagasaki missions, my go-to reference these days is John Coster-Mullen’s Atom Bombs: The Top Secret Insider Story of Little Boy and Fat Man. I first got a copy of John’s book in 2006 or so. John sent me a new copy a few months ago, and I have been impressed with how much new material he has added over the last 8 years. (And I have managed to find a few useful things for him over the years, which have made it into his book as well — duly credited!) If you’re interested in the history of the Manhattan Project, you can’t not have a copy of John’s book… and if your copy is over 5 years old, considered getting an updated edition! All of these little details about times and planes and whatnot come from John’s book.

So what caused the “heavy ground haze and smoke”?

Theory #1: Bad weather

The most common explanation for the obscuring of Kokura is one of weather. It seems to me to be a valid possibility, but let’s pick it apart a bit.

As noted, the Enola Gay had flown ahead to Kokura to scope out the visual conditions. They had radioed back that the visibility was “3/10 low clouds, no intermediate or high clouds, and forecast of improving conditions.”3 That was a favorable-enough weather report that Kokura, the primary target, was chosen as the first run. Upon arriving, however, Bockscar found the weather conditions were now 7/10 — too obscured to bomb. Is this plausible?

Summer weather patterns in Japan, map made in early 1945. Not great for bombing. Source: Produced for the USAAF's IMPACT magazine, high-res version via Fold3.com.

Summer weather patterns in Japan, map made in early 1945. Not great for bombing. Source: Produced for the USAAF’s IMPACT magazine, high-res version via Fold3.com. There is another wonderful map for winter weather as well.

General Groves, in his 1964 memoir, suggests that it might have been the case that the change in weather conditions was simply a matter of how much time had passed between the forecast and arrival of Bockscar. The strike plane was, as noted, delayed by around half an hour. Groves also implies that there may have been a difference between how visual the target was at an angle — how a bombardier sees it — and how it looks from straight above — how a weather plane sees it). He concludes that the reasons for the haze were “never determined.”4

On the face of it, it’s hard to know whether such a rapid change in visibility is possible through entirely natural causes. In some parts of the world, the weather can be very volatile. Japan is one of these parts of the world, especially around the late fall. The variability of Japanese weather conditions was something that the US Army Air Forces knew very well, and was one of the bane of their bombing plans. It was a major issue in the atomic bombing discussions as well since very early on. At the first Target Committee meeting in April 1945, weather was a major point of discussion:

…it was pointed out that the months in which the initial mission will be run constitute the worst weather months of Japan. […] Dennison pointed out that all weather maps indicated that there were only an average of 6 good bombing days in August and that of those 6 days a conservative estimate would probably result in safely predicting that we would have 3 good days in the month of August but these 3 good days could not be positively predicted in advance of more than 48 hours. 

Elsewhere in the memo it remarks that “3/10ths or less” cloud coverage was considered acceptable for visual bombing. It also notes that “only once in 6 years have there ever been 2 successive good visual bombing days of Tokyo,” which gives some indication of the weather’s variability.

Weather from the nearby city of Shimonoseki for August 8-9, 1945. Click to enlarge, or click here for the Excel file. Source: Japanese M

Weather from the nearby city of Shimonoseki for August 8-9, 1945. Click to enlarge, or click here for the Excel file. Source: Courtesy of the Japanese Meteorological Agency.

So it doesn’t seem impossible that it could have just been according to the weather, though the big difference between the conditions reported by the weather plane and the observed conditions by the strike plane seem, on the face of it, beyond what a half hour’s delay would accomplish. One question I don’t have the answer for is when the weather plane radioed those conditions back. In the case of the Hiroshima run, the weather plane was only 30 minutes earlier than the strike plane. If we assume that was a similar attempt on the second mission, it would mean that the strike plane was reaching the target over an hour after the weather plane had seen it, which could be a significant-enough delay for a serious change in visibility. (And another possibility is that the weather plane could have been, for whatever reason, incorrect — either at the wrong place or had its message garbled.)

There aren’t good weather records from this period, at least none I have seen. The closest site for state weather recording was in Shimonoseki, some 7 miles / 11 km northeast of Kokura. I asked the Japan Meteorological Agency for any records they had from that period and they sent me the above data.5 It is not especially helpful towards answering this question that I can see, but I’m not a meteorologist in the slightest. For me, the big take-away from the data is that it could go from totally clear to totally obscured over the course of an hour, which at least supports the plausibility of the weather theory.

Theory #2: Smoke from firebombing

One of the other causes put forward is that the “smoke and haze” seen over Kokura was actually a result of nearby firebombing. On August 8th, 1945, the 20th AF had sent 221 B-29s to the nearby city of Yahata (Yawata) to drop incendiary bombs.6 Yahata had been bombed several times during the war. It was, in fact, the site of the first B-29 attack on the Japanese homeland in June 1944, and indeed the first bombing attack against the Japanese homeland at all since the Doolittle raid. It had been bombed again in August 1944. The USAAF considered Yahata to be the largest steel producing center in the country, and dubbed it “the Pittsburgh of Japan.” It was the last Japanese city to be hit by a massive B-29 raid, a “night burn job” as a USAAF writer put it, and it was considered “leftover business” that had been scheduled to take place much earlier but delayed because of bad weather.7

Yahata/Yawata target map, March 1945. Kokura arsenal is visible to the east. Source: JapanAirRaids.org. Click here for the uncropped, unadjusted version.

Yahata/Yawata target map, March 1945. Kokura arsenal is visible to the east. Source: JapanAirRaids.org. Click here for the uncropped, unadjusted version.

The weather at Yahata had been 4/10 clouds over the target, but this didn’t matter for B-29 firebombing raids, because accuracy was not as big a concern as with the atomic bombs. The planes had arrived at Yahata around noontime. I’ve found very little in terms of documentation about how much of Yahata was burned out with this raid — perhaps because it was so late in the war, many of the traditional sources for information about incendiary bombing results (especially those contained on the invaluable website JapanAirRaids.org) essentially omit any discussion of this final big raid.

Could the bombing of Yahata have been the cause of the smoke that obscured Kokura? It doesn’t seem impossible, but it seems to me to be somewhat unlikely.

Approximate areas of interest in Yahata and Kokura, as seen on Google Earth today.

Approximate areas of interest in Yahata and Kokura, as seen on Google Earth today.

Bockscar was flying over Kokura just a little under 24 hours after the Yahata raid began. Incendiary raids did produce extreme amounts of smoke cover, as other photographic evidence indicates clearly. Yahata was only around 6 miles / 9 km west of Kokura (and their proximity is emphasized by the fact that both are today just considered wards of a larger city, Kitakyushu).

It seems odd that the Yahata smoke would have caught them off-guard. Wouldn’t the weather plane have noticed that there was smoke over Yahata rolling towards Kokura, or at least threatening it? Yahata is close enough that at the 30,000 feet or so that a weather plane would be flying over Kokura, all they would have to do is glance in its direction to see if there was heavy cloud cover. (One can easily replicate this experience with Google Earth if one chooses.) Could the smoke cloud have been lagged behind by just the amount of time that the weather plane wouldn’t see it, then rush ahead to obscure Kokura an hour later? Could the smoke have gone from non-obscuring to obscuring in just an hour? At the wind speeds measured at Shimonoseki (around 2-12 mph), it doesn’t strike me as super likely, but I’m not an expert in this kind of thing.

Theory #3: Japanese smokescreen

One last, more obscure theory. I first read of this in John Coster-Mullen’s book. I will quote him here:

When [Bockscar] finally arrived at 10:44 AM, smoke and industrial haze had obscured Kokura. Yahata had been firebombed by over 200 of LeMay’s B-29’s the previous day and the smoke had drifted over nearby Kokura. There was also a POW camp right next door to the main downtown power plan. An American prisoner in this camp reported later the Japanese had installed a large pipe that went from the power plant down to the river. He stated that whenever B-29’s were sighted over Kokura, the steam in the plant was diverted through this pipe and into the river. This created enormous condensation clouds that also helped to obscure the city.

John himself seems to have interviewed the POW camp survivor in question, and notes in a footnote that he thinks this was the first time this claim had surfaced in print. I certainly hadn’t seen it anywhere prior to John’s book. John asked Commander Ashworth about this in 1995, and Ashworth replied that this seemed possible, and added “if the Japanese really did that, then they were damn clever!”

German smokescreen use at Wilhelmshaven in June 1943. Caption: "Despite a smoke screen, 168 B-17s of the Eighth Air Force attacked Wilhelmshaven on 11 June. There are three lines of generators to windward of the area covered when the wind is in the north, as it was in this case. Generator boats are at the upper left. Despite the extent of the smoke screen hits are observed inside the circle..." Source: USAAAF IMPACT magazine, vol. 1, No. 5, August 1945, page 18.

German smokescreen use at Wilhelmshaven in June 1943. Caption: “Despite a smoke screen, 168 B-17s of the Eighth Air Force attacked Wilhelmshaven on 11 June. There are three lines of generators to windward of the area covered when the wind is in the north, as it was in this case. Generator boats are at the upper left. Despite the extent of the smoke screen hits are observed inside the circle…” Source: USAAAF IMPACT magazine, vol. 1, No. 5, August 1943, page 18.

A few weeks ago, there was a story carried by Japanese newspapers along these lines:

As the 69th anniversary of the Nagasaki atomic bombing approaches, a former mill worker in the present-day city of Kitakyushu, Fukuoka Prefecture, spoke about his untold story on how he burned coal tar to block the view of U.S. aircraft as they were about to drop the A-bomb on the city. … Of the three workers, Oita resident Satoru Miyashiro, 85, who worked at a can factory in the steel mill at around the end of the war said he burned coal tar to lay a smoke screen on Aug. 9, 1945. … Miyashiro said about two days before the Nagasaki attack Yawata steel workers learned that Hiroshima had been wiped out by the “new bomb” from their colleagues who had come back to Yawata via Hiroshima. He thought the next target would be his city as there were arms factories located in the area.

Note that this isn’t quite the same thing — this is someone in Yahata who was burning coal tar after hearing an air raid drill, and the smoke going downwind (east) to Kokura. I find it a little odd that the worker in question doesn’t mention that Yahata itself was firebombed less than a day before he decided to do this.

Are either of these theories plausible? In terms of, could they have done these things — of course. Turning on an incinerator is not an implausible action, and neither is the steam cloud scenario.

But would this have reduced the visibility over Kokura from 3/10 to 7/10 in the time it took the strike plane to get there? I’m not an atmospheric scientist, so I wouldn’t want to hazard a strong position on this. One can presumably model both of these scenarios and see if either were possible. I would be extremely interested if anyone wanted to that!

Susquehanna Steam Electric Station — just an example of what a very large nuclear power plant can generate in terms of steam. It's a lot of steam. Could it obscure a city downwind of it from a B-29 bomber? Image source.

Susquehanna Steam Electric Station — just an example of what a very large nuclear power plant can generate in terms of steam. It’s a lot of steam. Could it obscure a city downwind of it from a B-29 bomber? Image source.

My gut thought is that they were not super likely to be wholly responsible for the cloud cover. If it had been steam from a single plant, I suspect someone on Bockscar would have noted it as such. We have lots of experience with steam-generating power plants — think of the clouds created by nuclear cooling towers. They certainly can put out a lot of steam. Would it be enough to block off the entire city? I’m kind of dubious.

What about the coal tar possibility? I’m especially dubious that this would have been enough. Setting up honest-to-god smokescreen for an entire city is hard work, even if you are a professional. When the Germans wanted to protect individual places (like plants) from bombers they set up dozens to hundreds of smoke pots to do the job, or used multiple dedicated smoke generators. Some of the larger smokescreen images I have found clearly involve lots of smoke sources placed at good intervals upwind of the target they are meant to protect. So I don’t know.

On the other hand, if the smoke from Yahata was not from the firebombing but instead something deliberate, it would explain the time delay issue. If the wind was going due east at around 5 mph, that would in fact be perfect for putting a smoke cover over Kokura. So it has its merits as a theory.

Conclusion

There are narrative aspects of each theory that appeal, and each of them change what is meant by the “luck of Kokura.” If bad weather is what saved Kokura, then it becomes a metaphor for how serendipitously life and death are dealt out by the hands of fate. If it was smoke from the firebombing of Yahata, then it becomes an ironic story about the Army Air Forces’ zeal for destruction could become counterproductive. If it was the result of deliberate action on behalf of the Japanese, then it becomes something much more complicated, a story about how individual action may have led to the saving of some lives… and the dooming of others. It also would change the standard story of how defenseless the Japanese were against these weapons.

The bombing of Nagasaki. Original source. Slightly edited to improve foreground/background distinction.

Of course, what was lucky for Kokura was not so for Nagasaki.

Looking at these three options, I find the weather theory the easiest one to stomach. Japanese weather patterns were notoriously hard to predict and it was known as the worst season for bombing conditions. That they could change over an hour seems unsurprising to me, especially for a coastal city, where clouds can come and go which impressive rapidity (as someone who has lived in the Berkeley, Boston, and New York areas can attest). I like the irony of the Yahata story, but there are things that just don’t add up — I don’t see why the weather plane would not have mentioned it, and it seems implausible to me that it would take almost exactly 24 hours for the heavy cloud cover to have migrated a mere 5-10 miles. And for reasons indicated, I’m not sure I buy the smokescreen story — it would have been really difficult to pull off that degree of cloud cover reliably. It would have taken tremendous foresight and luck. And it is strange that this story would be “buried” for so long. This doesn’t mean that someone didn’t try it (I am emphatically not calling anyone a liar!). It just means that I’m not sure it would have worked even if they did try it.

A separate possibility is “all of the above.” Maybe the weather was bad. Maybe there was haze from the Yahata bombing. Maybe someone did try to release steam or smokescreen. Maybe all of these things occurred at once, making “the luck of Kokura” something that was the result of multiple causes. That would make Kokura extra lucky, I suppose, and not fit into any of the above pat narratives. And make Nagasaki extra un-lucky in turn.

In the end, it doesn’t really matter which of these things happened. The bare fact is that Kokura didn’t get bombed and Nagasaki did. But I find looking into these kinds of questions useful as a historian. Too often it is easy to take for granted that the explanations given in narrative works of history are “settled,” when really they are often resting on very thin evidence, thinner perhaps than the historian who writes them realizes. I don’t think we really know what happened at Kokura, and I’m not sure we ever truly will.

Notes
  1. Sometimes you see it as “Bock’s Car,” but it said “Bockscar” on the side of the B-29. This is one of those places where I say, “who cares?” but purists are concerned with this kind of detail. []
  2. Flight diary of Lt. Fred Olivi, quoted in Coster-Mullen’s book. []
  3. Bockscar flight log by Commander Frederick Ashworth, included in Norman F. Ramsey, “History of Project A,” (27 September 1945). A full of copy of Ramsey’s report is included in Coster-Mullen’s Atom Bombs book. []
  4. Leslie Groves, Now it Can Be Told, 345: “At Kokura, they found that visual bombing was not possible, although the weather plane had reported that it should be. Whether this unexpected condition was due to the time lag, or to the difference between an observer looking straight down and a bombardier looking at the target on a slant, was never determined.” []
  5. Here is the original Excel file they sent me. []
  6. Most US sources list the city as “Yawata,” but it apparently corresponds with what is today transliterated as the city of Yahata, in Fukoka prefecture, and there is an entirely different city known as Yawata in Kyoto Prefecture. The kanji is the same. Yahata has since been absorbed by Kitakyushu, along with Kokura. []
  7. Tom Prideaux, “Mission to Yawata, 7 Aug. 1945,” IMPACT, vol. 3, no. 9 (September-October 1945), 53. []