Posts Tagged ‘Manhattan Project’


Silent Nagasaki

Friday, February 7th, 2014

Teaching and other work has bogged me down, as it sometimes does, but I’m working on a pretty fun post for next week. In the meantime, here is something I put together yesterday. This is unedited (in the sense that I didn’t edit it), “raw” footage of the loading of the Fat Man bomb into the Bockscar plane on the island of Tinian, August 9th, 1945. It also features footage of the bombing of Nagasaki itself. I got this from Los Alamos historian Alan Carr a while back. I’ve added YouTube annotations to it as well, calling out various things that are not always known.

You have probably seen snippets of this in documentaries and history shows before. But I find the original footage much more haunting. It was filmed without sound, so any sound you hear added to this kind of footage is an artifact of later editing. The silent footage, however, makes it feel more “real,” more “authentic.” It removes the Hollywood aspect of it. In that way, I find this sort of thing causes people to take the events in the footage more seriously as an historical event, rather than one episode in “World War II, the Movie.”

I posted it on Reddit as well, and while there was some share of nonsense in the ~700 comments that it accrued, there was also a lot of expression of empathy and revelation, and a lot of good questions being asked (e.g. Did the people loading Fat Man into the plane know what they were loading? Probably more than the people who loaded Little Boy did, because they knew what had happened at Hiroshima). So I think some learning has happened, and I think the fact that this has gotten +100,000 views in just a day is some sign that there is quite an audience out there for this sort of stripped-down history.

There is also Hiroshima footage, but it isn’t quite as good, on the whole. It is largely concerned with the crew of the plane taking off and arriving. Which is interesting, in a sense, but visually doesn’t mean much unless you know who everybody is.

There is a lot of Trinity test footage as well which I will upload and annotate in the future as well.

Until next week!


The trouble with airbursts

Friday, December 6th, 2013

Both the Little Boy and Fat Man atomic bombs were detonated high in the air above their target cities. That they did this was no accident — specialized circuitry, some invented just for the atomic bombs, was used so that the bombs could detect their height off of the ground and detonate at just the right moment. Little Boy detonated 1,968±50 feet above Hiroshima, Fat Man detonated 1,650±10 feet above Nagasaki. At least as early as the May 1945 Target Committee meeting at Los Alamos, “the criteria for determining height” of detonation had been agreed upon: the goal was to maximize the 5 psi (pounds-per-square-inch) overpressure blast radius of the bombs, with a knowledge that this was going to be a tricky thing since they weren’t really sure how explosively large the bombs would be, and a bomb either too big or too large would reduce the total range of the 5 psi radius. At the time, they estimated Little Boy would be between 5 and 15 kilotons, Fat Man between 0.7 and 5 kilotons — obviously this was pre-”Trinity,” which showed the Fat Man model could go at least up to 18-20 kilotons.

I was on the road quite a lot the last month, so I apologize about the radio silence for the past couple of weeks. But I’m happy to report to you that I managed to recently update the NUKEMAP’s effects code in a way I’ve been meaning to for a long while: you can now set arbitrary heights for detonations. I thought I would explain a little bit about how that works, and why that matters, in today’s post.

The 1962 edition of Glasstone and Dolan's The Effects of Nuclear Weapons and the Lovelace Foundation's "Nuclear Bomb Effects Computer."

The 1962 edition of Glasstone’s The Effects of Nuclear Weapons and the Lovelace Foundation’s “Nuclear Bomb Effects Computer.”

Why did it take me so long to add a burst height feature? (A feature that, to both me and many others alike, was obviously lacking.) Much of the NUKEMAP’s code is based on the calculations that went into making the famous Lovelace Foundation “Nuclear Bomb Effects Computer,” which itself were based on equations in Samuel Glasstone’s classic The Effects of Nuclear Weapons. This circular slide rule has some wonderful retro charm, and is a useful way of boiling down a lot of nuclear effects data into a simple analog “computer.” However, like most nuclear effects calculations, it wasn’t really designed with the kind of visualization that the NUKEMAP had in mind. For something like the NUKEMAP, one wants to be able to plug in a yield and a “desired” overpressure (such as 5 psi), and get a measurement of the ground range of the effect as a result. But this isn’t how the Lovelace Computer works. Instead, you put in your kilotonnage and the distance you want to know the overpressure at, and in return you get a maximum overpressure in the form of pounds-per-square-inch. In other words, instead of asking, “what’s the distance for 5 psi for a 15 kiloton surface burst?,” you are only allowed to ask, “if I was 2 miles from a 15 kiloton surface burst, what would the overpressure be?”

For surface bursts and a few low height (400 feet and under) airbursts, the Lovelace Foundation did, in a separate report, provide equations of the sort useful for the NUKEMAP, and the NUKEMAP’s code was originally based on these. But they didn’t allow for anything fancy with regards to arbitrary-height airbursts. They let one look for pressure information at “optimal” airburst heights, but did not let one actually set a specific airburst height. For awhile I thought this might just have been a strange oversight, but the more I dug into the issue, I realized this was probably because the physics of airbursts is hard.

Grim geometry: calculating the ground range of the 500 rem radiation exposure radius for a Hiroshima-sized nuclear weapon set off at the height of the Hiroshima bomb. Most objects roughly to scale.

Grim geometry: calculating the ground range of the 500 rem radiation exposure radius for a Hiroshima-sized nuclear weapon set off at the height of the Hiroshima bomb. Most objects roughly to scale.

There are three immediate effects of nuclear weapons that the NUKEMAP models: thermal radiation (heat), ionizing radiation (radioactivity), and overpressure (blast). Thermal and ionizing radiation pretty much travels in a straight line, so if you know the slant-line distance for a given effect, it’s no problem figuring out the ground distance at an arbitrary height through a simple application of the Pythagorean theorem, as shown above. The report the Lovelace Computer was based on allowed for the calculation of slant-line airburst distances for both of these, so that was a snap to implement. Somewhat interestingly, the ranges of the “interesting” thermal radiation categories (e.g. burns and burning) are so large that except with very high airbursts one often finds almost no difference between ground ranges computed using slant versus straight-line distances. Ionizing radiation, however, is relatively short in its effects, and so the height of the burst really does matter in practical terms for how much radiation the ground receives. This has a relevance to Hiroshima and Nagasaki that I will return to.

But this isn’t how the physics of blast pressure wrks. The reason is somewhat subtle but important for understanding nuclear weapons targeting decisions. The pressure wave that emerges from the nuclear fireball does not stop when it hits the ground. Rather, it reflects — bounces upward again — like so:

Reflection of the shockwave of a 20 kiloton nuclear explosion exploded at 1,770 foot altitude. Via Wikipedia.

Reflection of the shockwave of a 20 kiloton nuclear explosion exploded at 1,770 foot altitude. Via Wikipedia.

You don’t have to take my word for it (or Wikipedia’s, for that matter) — you can actually see the reflection of the shockwave in some nuclear testing photography, like this photograph of Shot Grable, the “atomic cannon” test from 1953:

Shot Grable, Operation Upshot-Knothole — a 15 kiloton nuclear artillery shell detonated at an altitude of 524 feet.

Shot Grable, Operation Upshot-Knothole — a 15 kiloton nuclear artillery shell detonated at an altitude of 524 feet, with the reflection of the blast wave clearly visible under the fireball.

The initial blast wave is the “incident” or “primary” blast wave. The bounded wave in the “reflected” wave. When they touch, as shown in the Wikipedia diagram, they combine — which dramatically increases the overpressure at that location. So, referring the Wikipedia diagram again, by the time the primary shockwave was at the final radius of the diagram, it would have lost a considerable amount of energy. But when it merges with the reflected shockwave, it forms a single, vertical shock front known as the “Mach stem.” In the diagram above, that has an overpressure of 15 psi — enough to destroy pretty significant buildings. If the shockwave did not work in this fashion, the primary shockwave would itself be considerably less than 15 psi at that point.

So the overall point here is that blast reflection can dramatically increase the blast pressure of the bomb at the point where it occurs. But the location at this point varies depending on the height of the bomb detonation — so you can use the choice of bomb detonation altitude to maximize certain pressures in particular. So this is what the Target Committee was talking about in May 1945: they wanted to maximize the radius of the 5 psi overpressure range, and they recognized that this involved finding the correct detonation height and knowing the correct yield of the bomb. They knew about the reflection property and in fact referred to the Mach stem explicitly in their discussion. Why 5 psi? Because that is the overpressure used to destroy “soft” targets like the relatively flimsy houses used by Japanese civilians, which they had already realized would be much easier to destroy than German-style houses.

For the NUKEMAP, this reflection made the modeling difficult. There are lots of models out there for calculating overpressure based on altitude, but they all do it similar to the Lovelace Foundation’s “Computer”: they tell you the maximum overpressure at a pre-specified point from ground zero. They don’t let you ask, “where would the 5 psi radius be for a blast of 15 kilotons and a height of 1,968 feet?” Which was inconvenient for me. The data is out there, though — just not in computational form. Graphs of pressure ranges plotted on axes of ground range and burst height are quite common in the nuclear literature, where they are sometimes known as “knee curves” because of the characteristic “bulge” in ground range produced by the aforementioned Mach reflection, the spot where the pressure range dramatically enlarges. Glasstone and Dolan’s 1977 Effects of Nuclear Weapons contains three of these graphs for pressure ranges between 10,000 and 1 psi. Here is the “low-pressure” graph showing the characteristic “knees”:

Glasstone and Dolan Fig 3-73c - Peak overpressures

Reading these is fairly straightforward once you understand what they show. If you want to maximize the 2 psi pressure range, find the point at which the “2 psi” curve is as far to the right as possible. Then look at the vertical axis to find what the corresponding height of burst is. Or, if you want to know what the pressure will be on the ground at a given distance from a bomb detonated at a given burst height, simply figure out which pressure regions that point is between on the graph. The graphs are always given for 1 kiloton bursts, but scaling from these to arbitrary detonations (with the caveat that very high and very low yields can sometimes be a little different) is pretty straightforward according to the scaling laws given in the text.

I searched high and low for a computational solution to the airburst question, without much luck. I had attempted to do polynomial curve fits on the graphs above, and just found them to be too irregular — the equations I was able to produce made huge errors, and splitting them up into sub-curves produced a mathematical mess. The only other computational solution I found was someone else who had done curve fits and also come up with equations that produced relatively large errors. I wasn’t happy with this. I discussed my frustrations with a few people (let me do a shout out to Edward Geist, currently a Stanton Fellow at the Rand Corporation, who has been doing his own modeling work regarding Soviet nuclear effects handbooks, and to Alex Montgomery at Reed College, both of whom were extremely helpful as people to talk to about this), and gradually came to the conclusion that there probably wasn’t an obvious analytical solution to this problem. So I did the next-best thing, which was to take samples of all of the curve values (less tedious than it sounds because of a little script I whipped up for the job) and just set up some tables of data that could then be sifted through very quickly by the computer. In other words, the way the NUKEMAP’s code works is pretty much the Javascript equivalent to consulting the graphs in Glasstone and Dolan’s book — it treats it as a simple interpolation problem between known values. Which turns out to give results which are no worse than those involved with using the book itself:

The NUKEMAP's overpressure data, graphed using R. Point samples are represented by circles, lines connect given pressure ranges. Color corresponds (logarithmically) with pressure ranges from 1 to 10,000 psi.

The NUKEMAP’s overpressure data, graphed using R. Point samples are represented by circles, lines connect given pressure ranges. Color corresponds (logarithmically) with pressure ranges from 1 to 10,000 psi. Unknown points on the graph are interpolated between known values.

The end result is that now the NUKEMAP can do arbitrary-burst height airbursts. In fact, the NUKEMAP pressure model goes all the way up to 10,000 psi — a pressure zone equivalent to being 4 miles under the ocean. Yow.

With this data in hand, and the NUKEMAP model, let’s go back to the Hiroshima and Nagasaki question. They knew about the Mach reflection, they knew about the height of the burst. It’s not clear that their assumptions for how this would work would line up exactly with those in Glasstone and Dolan, since those were modified according to actual empirical experience with airbursts in the kiloton range, something that they did not have on hand in 1945, even if they intuited much of the physics behind it. What can we say about their knowledge, and their choices, with regards to what they actually did with selecting the blast heights?

The Hiroshima yield has been calculated as about 15 kilotons, and the Nagasaki yield was about 21 kilotons. According to the Glasstone and Dolan model, to optimize the 5 psi pressure range for each, you’d want a burst height of ~2,500 feet for Little Boy and ~2,800 feet for Fat Man. Those are significantly higher altitudes than the actual detonation heights of 1,968 and 1,650 feet. The Target Committee meeting shows that they were assuming that 2,400 feet was the correct height for a 15 kiloton bomb — which is about right. Which means either than the detonating circuitry fired late (not impossible though I haven’t seen it mentioned), or they changed their blast range criteria (for a 15 kiloton bomb, 1,940 feet maximizes the 9 psi radius rather than the 5 psi radius), or that they were being very conservative about the yields (a 1,960 feet burst height corresponds with maximizing the 5 psi radius of a 7 kiloton burst, whereas 1,700 feet corresponds to a 5 kiloton burst). My guess is that the latter was what was going on — they were being very conservative about the yield.

The net result is that at both Hiroshima and Nagasaki, you had lower burst heights than were optimal. The effect on the ground is that while the 5 psi blast radius didn’t go quite as far out as it might have ideally, the range of radiation effects and radiation around Ground Zero was significantly increased, and the maximum overpressures around Ground Zero were substantially higher. Overall, it is interesting to see that they were apparently, even after Trinity, still being pretty un-optimistic regarding the explosive yields of the bombs, calibrating their burst heights to half or even one quarter of what the actual blasts were. For a “soft” targets, like Hiroshima and Nagasaki, this doesn’t matter too much, as long as the fireball is above the altitude which produces local fallout, but for a “hard” target, where the goal is to put a lot of pressure in one spot, this would be a serious miscalculation.


Liminal 1946: A Year in Flux

Friday, November 8th, 2013

There are lots of important and exciting years that people like to talk about when it comes to the history of nuclear weapons. 1945 obviously gets pride of place, being the year of the first nuclear explosion ever (Trinity), the first  and only uses of the weapons in war (Hiroshima and Nagasaki), and the end of World War II (and thus the beginning of the postwar world). 1962 gets brought up because of the Cuban Missile Crisis. 1983 has been making a resurgence in our nuclear consciousness, thanks to lots of renewed interest in the Able-Archer war scare. All of these dates are, of course, super important.

Washington Post - January 1, 1946

But one of my favorite historical years is 1946. It’s easy to overlook — while there are some important individual events that happen, none of them are as cataclysmic as some of the events of the aforementioned years, or even some of the other important big years. But, as I was reminded last week while going through some of the papers of David Lilienthal and Bernard Baruch that were in the Princeton University archives, 1946 was something special in and of itself. It is not the big events that define 1946, but the fact that it was a liminal year, a transition period between two orders. For policymakers in the United States, 1946 was when the question of “what will the country’s attitude towards the bomb be?” was still completely up for grabs, but over the course of the year, things became more set in stone.

1946 was a brief period when anything seemed possible. When nothing had yet calcified. The postwar situation was still fluid, and the American approach towards the bomb still unclear.

Part of the reason for this is because things went a little off the rails in 1945. The bombs were dropped, the war had ended, people were pretty happy about all of that. General Groves et al. assumed that Congress would basically take their recommendations for how the bomb should be regarded in the postwar (by passing the May-Johnson Bill, which military lawyers, with help from Vannevar Bush and James Conant, drafted in the final weeks of World War II). At first, it looked like this was going to happen — after all, didn’t Groves “succeed” during the war? But in the waning months of 1945, this consensus rapidly deteriorated. The atomic scientists on the Manhattan Project who had been dissatisfied with the Army turned out to make a formidable lobby, and they found allies amongst a number of Senators. Most important of these was first-term Senator Brien McMahon, who quickly saw an opportunity to jump into the limelight by making atomic energy his issue. By the end of the year, not only did Congressional support fall flat for the Army’s Bill, but even Truman had withdrawn support for it. In its place, McMahon suggested a bill that looked like something the scientists would have written — a much freer, less secret, civilian-run plan for atomic energy.

So what happened in 1946? Let’s just jot off a few of the big things I have in mind.

January: The United Nations meets for the first time. Kind of a big deal. The UN Atomic Energy Commission is created to sort out questions about the future of nuclear technology on a global scale. Hearings on the McMahon Bill continue in Congress through February.

Igor Gouzenko (masked) promoting a novel in 1954. The mask was to help him maintain his anonymity, but you have to admit it adds a wonderfully surreal and theatrical aspect to the whole thing.

Igor Gouzenko (masked) promoting a novel in 1954. The mask was to help him maintain his anonymity, but you have to admit it adds a wonderfully surreal and theatrical aspect to the whole thing.

February: The first Soviet atomic spy ring is made public when General Groves leaks information about Igor Gouzenko to the press. Groves wasn’t himself too concerned about it — it was only a Canadian spy ring, and Groves had compartmentalized the Canadians out of anything he considered really important — but it served the nice purpose of dashing the anti-secrecy lobby onto the rocks.

Also in February, George F. Kennan sends his famous “Long Telegram” from Moscow, arguing that the Soviet Union sees itself in essential, permanent conflict with the West and is not likely to liberalize anytime soon. Kennan argues that containment of the USSR through “strong resistance” is the only viable course for the United States.

March: The Manhattan Engineer District’s Declassification Organization starts full operation. Groves had asked the top Manhattan Project scientists to come up with the first declassification rules in November 1945, when he realized that Congress wasn’t going to be passing legislation as soon as he expected. They came up with the first declassification procedures and the first declassification guides, inaugurating the first systematic approach to deciding what was secret and what was not.

Lilienthal's own copy of the mass-market edition of the Acheson-Lilienthal Report, from the Princeton University Archives.

Lilienthal’s own copy of the mass-market edition of the Acheson-Lilienthal Report, from the Princeton University Archives.

March: The Acheson-Lilienthal Report is completed and submitted, in secret, to the State Department. It is quickly leaked and then was followed up by a legitimate publication by the State Department. Created by a sub-committee of advisors, headed by TVA Chairman David Lilienthal and with technical advice provided by J. Robert Oppenheimer, the Acheson-Lilienthal Report argued that the only way to a safe world was through “international control” of atomic energy. The scheme they propose is that the United Nations create an organization (the Atomic Development Authority) that would be granted full control over world uranium stocks and would have the ability to inspect all facilities that used uranium in significant quantities. Peaceful applications of atomic energy would be permitted, but making nuclear weapons would not be. If one thought of it as the Nuclear Non-Proliferation Treaty, except without any authorized possession of nuclear weapons, one would not be too far off the mark. Of note is that it is an approach to controlling the bomb that is explicitly not about secrecy, but about physical control of materials. It is not loved by Truman and his more hawkish advisors (e.g. Secretary of State Byrnes), but because of its leak and subsequent publication under State Department header, it is understood to be “the” position of the United States government on the issue.

April: The McMahon Act gets substantial modifications while in committee, including the creation of a Military Liaison Committee (giving the military an official position in the running of the Atomic Energy Commission) and the introduction of a draconian secrecy provision (the “restricted data” concept that this blog takes its name from).

June: The Senate passes the McMahon Act. The House starts to debate it. Several changes are made to the House version of the bill — notably all employees with access to “restricted data” must now be investigated by the FBI and the penalty for misuse or espionage of “restricted data” is increased to death or life imprisonment. Both of these features were kept in the final version submitted to the President for signature in July.

June: Bernard Baruch, Truman’s appointee to head the US delegation of the UN Atomic Energy Commission, presents a modified form of the Acheson-Lilienthal Report to the UNAEC, dubbed the Baruch Plan. Some of the modifications are substantial, and are deeply resented by people like Oppenheimer who see them as torpedoing the plan. The Baruch Plan, for example, considered the question of what to do about violations of the agreement something that needed to be hashed out explicitly and well in advance. It also argued that the United States would not destroy its (still tiny) nuclear stockpile until the Soviet Union had proven it was not trying to build a bomb of their own. It was explicit about the need for full inspections of the USSR — a difficulty in an explicitly closed society — and stripped the UN Security Council of veto power when it came to enforcing violations of the treaty. The Soviets were, perhaps unsurprisingly, resistant to all of these measures. Andrei Gromyko proposes a counter-plan which, like the Baruch Plan, prohibits the manufacture and use of atomic weaponry. However, it requires full and immediate disarmament by the United States before anything else would go into effect, and excludes any international role in inspection or enforcement: states would self-regulate on this front.

Shot "Baker" of Operation Crossroads — one of the more famous mushroom clouds of all time. Note that the mushroom cloud itself is not the wide cloud you see there (which is a brief condensation cloud caused by it being an underwater detonation), but is the more bulbous cloud you see peaking out of the top of that cloud. You can see the battleships used for target practice near base of the cloud. The dark mark on the right side of the stem may be an upturned USS Arkansas.

Shot “Baker” of Operation Crossroads — one of the more famous mushroom clouds of all time. Note that the mushroom cloud itself is not the wide cloud you see there (which is a brief condensation cloud caused by it being an underwater detonation), but is the more bulbous cloud you see peaking out of the top of that cloud. You can see the battleships used for target practice near base of the cloud. The dark mark on the right side of the stem may be an upturned USS Arkansas.

July: The first postwar nuclear test series, Operation Crossroads, begins in the Bikini Atoll, Marshall Islands. Now this is a curious event. Ostensibly the United States was in favor of getting rid of nuclear weapons, and in fact had not yet finalized its domestic legislation about the bomb. But at the same time, it planned to set off three of them, to see their effect on naval vessels. (They decided to only set off two, in the end.) The bombs were themselves still secret, of course, but it was decided that this event should be open to the world and its press. Even the Soviets were invited! As one contemporary report summed up:

The unique nature of the operation was inherent not only in its huge size — the huge numbers of participating personnel, and the huge amounts of test equipment and number of instruments involved — it was inherent also in the tremendous glare of publicity to which the tests were exposed, and above all the the extraordinary fact that the weapons whose performance was exposed to this publicity were still classified, secret, weapons, which had never even been seen except by a few men in the inner circles of the Manhattan District and by those who had assisted in the three previous atomic bomb detonations. It has been truly said that the operation was “the most observed, most photographed, most talked-of scientific test ever conducted.” Paradoxically, it may also be said that it was the most publicly advertised secret test ever conducted.1

August: Truman signs the McMahon Act into law, and it becomes the Atomic Energy Act of 1946. It stipulates that a five-person Atomic Energy Commission will run all of the nation’s domestic atomic energy affairs, and while half of the law retains the “free and open” approach of the early McMahon Act, the other half has a very conservative and restrictive flavor to it, promising death and imprisonment to anyone who betrays atomic secrets. The paradox is explicit, McMahon explained at the time, because finding a way to implement policy between those two extremes would produce rational discussion. Right. Did I mention he was a first-term Senator? The Atomic Energy Commission would take over from the Manhattan Engineer District starting in 1947.

A meeting of the UN Atomic Energy Commission in October 1946. Bernard Baruch is the white-haired man sitting at the table at right behind the “U.S.A” plaque. At far top-right of the photo is Robert Oppenheimer. Two people above Baruch, in the very back, is General Groves. Directly below Groves is Manhattan Project scientist Richard Tolman. British physicist James Chadwick sits directly behind the U.K. representative at the table.

A meeting of the UN Atomic Energy Commission in October 1946. At front left, speaking, is Andrei Gromyko. Bernard Baruch is the white-haired man sitting at the table at right behind the “U.S.A” plaque. At far top-right of the photo is a pensive J. Robert Oppenheimer. Two people above Baruch, in the very back, is a bored-looking General Groves. Directly below Groves is Manhattan Project scientist Richard Tolman. British physicist James Chadwick sits directly behind the U.K. representative at the table.

September: Baruch tells Truman that international control of atomic energy seems nowhere in sight. The Soviet situation has soured dramatically over the course of the year. The Soviets’  international control plan, the Gromyko Plan, requires full faith in Stalin’s willingness to self-regulate. Stalin, for his part, is not willing to sign a pledge of disarmament and inspection while the United States is continuing to build nuclear weapons. It is clear to Baruch, and even to more liberal-minded observers like Oppenheimer, that the Soviets are probably not going to play ball on any of this, because it would not only require them to forswear a potentially important weapon, but because any true plan would require them to become a much more open society.

October: Truman appoints David Lilienthal as the Chairman of the Atomic Energy Commission. Lilienthal is enthusiastic about the job — a New Deal technocrat, he thinks that he can use his position to set up a fairly liberal approach to nuclear technology in the United States. He is quickly confronted by the fact that the atomic empire established by the Manhattan Engineer District has decayed appreciably in year after the end of the war, and that he has powerful enemies in Congress and in the military. His confirmation hearings start in early 1947, and are exceptionally acrimonious. I love Lilienthal as an historical figure, because he is an idealist who really wants to accomplish good things, but ends up doing almost the opposite of what he set out to do. To me this says a lot about the human condition.

November: The US Atomic Energy Commission meets for the first time in Oak Ridge, Tennessee. They adopt the declassification system of the Manhattan District, among other administrative matters.

December: Meredith Gardner, a cryptanalyst for the US Army Signal Intelligence Service, achieves a major breakthrough in decrypting wartime Soviet cables. A cable from 1944 contains a list of scientists working at Los Alamos — indications of a serious breach in wartime atomic security, potentially much worse than the Canadian spy ring. This information is kept extremely secret, however, as this work becomes a major component in the VENONA project, which (years later) leads to the discovery of Klaus Fuchs, Julius Rosenberg, and many other Soviet spies.

On Christmas Day, 1946, the Soviet Union’s first experimental reactor, F-1, goes critical for the first time.

The Soviet F-1 reactor, in 2009. It remains operational today — the longest-lived nuclear reactor by far.

The Soviet F-1 reactor, in 2009. It remains operational today — the longest-lived nuclear reactor by far.

No single event on that list stands out as on par with Hiroshima, the Cuban Missile Crisis, or even the Berlin Crisis. But taken together, I think, the list makes a strong argument for the importance of 1946. When one reads the documents from this period, one gets this sense of a world in flux. On the one hand, you have people who are hoping that the re-ordering of the world after World War II will present an enormous opportunity for creating a more peaceful existence. The ideas of world government, of the banning of nuclear weapons, of openness and prosperity, seem seriously on the table. And not just by members of the liberal elite, mind you: even US Army Generals were supporting these kinds of positions! And yet, as the year wore on, the hopes began to fade. Harsher analysis began to prevail. Even the most optimistic observers started to see that the problems of the old order weren’t going away anytime soon, that no amount of good faith was going to get Stalin to play ball. Which is, I should say, not to put all of the onus on the Soviets, as intractable as they were, and as awful as Stalin was. One can imagine a Cold War that was less tense, less explicitly antagonistic, less dangerous, even with limitations that the existence of a ruler like Stalin imposed. But some of the more hopeful things seem, with reflection, like pure fantasy. This is Stalin we’re talking about, after all. Roosevelt might have been able to sweet talk him for awhile, but even that had its limits.

We now know, of course, that the Soviet Union was furiously trying to build its own atomic arsenal in secret during this entire period. We also know that the US military was explicitly expecting to rely on atomic weapons in any future conflict, in order to offset the massive Soviet conventional advantage that existed at the time. We know that there was extensive Soviet espionage in the US government and its atomic program, although not as extensive as fantasists like McCarthy thought. We also know, through hard experience, that questions of treaty violations and inspections didn’t go away over time — if anything, I think, the experience of the Nuclear Non-Proliferation Treaty has shown that many of Baruch’s controversial changes to the Acheson-Lilienthal Report were pretty astute, and quickly got to the center of the political difficulties that all arms control efforts present.

As an historian, I love periods of flux and of change. (As an individual, I know that living in “interesting times” can be pretty stressful!) I love looking at where old orders break down, and new orders emerge. The immediate postwar is one such period — where ideas were earnestly discussed that seemed utterly impossible only a few years later. Such periods provide little windows into “what might have been,” alternative futures and possibilities that never happened, while also reminding us of the forces that bent things to the path they eventually went on.

  1. Manhattan District History, Book VIII, Los Alamos Project (Y) – Volume 3, Auxiliary Activities, Chapter 8, Operation Crossroads (n.d., ca. 1946). []

How many people worked on the Manhattan Project?

Friday, November 1st, 2013

Everyone knows the Manhattan Project was big. But how big was it? There are lots of ways to try and convey the bigness. The size of the buildings and sites, for example. Or the cost — $2 billion 1945 USD, which doesn’t sound that big, even when converted to modern numbers (e.g. around $30 billion 2012 USD, depending on the inflator you use), since we’re used to billions being tossed around like they are nothing these days. But consider that the USA spent about $300 billion on World War II as a whole — so that means that the atomic bombs made up for a little under 1% of the cost of the entire war. Kind of impressive, but even then, it’s hard to wrap one’s head around something like “the cost of World War II.”

General Groves speaks to a group of Oak Ridge service personnel in August 1945. From the DOE. There are lots of great Oak Ridge photos from the 1940s in this Flickr set.

General Groves speaks to a group of Oak Ridge service personnel in August 1945. From the DOE. There are lots of great Oak Ridge photos from the 1940s in this Flickr set.

Another approach is to talk about how many people were involved. There are a number of various estimates floating around. Instead of focusing on those, I want to jump directly to the source: a once-secret postwar report on Manhattan Project personnel practices that includes some raw numbers on hiring.1

This report has two very interesting graphs in it. The first is this one, showing total employment by month, broken into the various important Manhattan Project categories:

Manhattan Project contractor employment by month

Let’s just take a moment to marvel at this. They went from pretty much just talking about a bomb, in theory, on paper, in late 1942, and had a project with 125,310 active employees at its peak, 22 months later. That’s a huge ramp-up.

I like this graph because it helps you see, very plainly, the progress of the project. You can see that Oak Ridge (CEW) and Hanford (HEW) construction both got rolling pretty quickly but took about a year to hit their maximums, and that all construction peaked in early 1944. At which point, operations became the main issue — running the plants. It’s interesting to compare how many more people were required for Oak Ridge operations than Hanford operations, and that the “Santa Fe Operations” — Los Alamos, et al. — barely registers on the graph. A couple thousand people at most.

You can also see how rapidly that curve starts to drop off in September 1945 — over 10,000 people left at the end of the war, a significant chunk of them being Oak Ridge operations personnel. There is then a long slumping decline until late 1946, when you start to get an up-tick. This maps on pretty well with what we know about the history of the Manhattan Project in the period before the Atomic Energy Commission took over: Groves’ hard-built empire decayed under the uncertainty of the postwar and the dithering of Congress.

This is where we get the number one usually sees cited for the Manhattan Project: 125,000 or so employees at its peak. Which is impressive… but also kind of misleading. Why? Because peak employment is not cumulative employment. That is, the number of people who work at any given company today are not the number of people who have worked there over the course of its lifetime. Obvious enough, but if one is wondering how many people did it take to make the atomic bomb, one wants to know the cumulative employment, not the number on hand at any one time, right?

Digging around a bit more in the aforementioned personnel statistics of the Manhattan Project (a thrilling read, I assure you), I found this rather amazing graph of the total number of hires and terminations by the project:

Manhattan District Contractors Hires and Terminations through 31 December 1946

Now that number on the left, the total hires, is a pretty big one — over 600,000 total. Unlike the other graph, I don’t have the exact figure for this, but it looks to be around 610,000. That’s a huge number. Why would the numbers be at such odds? Because at the big sites — Oak Ridge and Hanford — there was a pretty high rate of turnover, as the “terminations” bar indicates: over 560,000 people left their jobs on the Manhattan Project by December 1946.

Some of this, of course, is because the job was done and they went home — once the construction was done, you didn’t need as many people working on construction anymore. But it’s also because even during the war, there was a considerable amount of people either quitting or getting fired. People left their jobs all the time, at all times during the war. As the report indicates, the reasons and rates varied by site. For construction at Hanford, they had an average monthly turnover rate of 20%, with a ratio of resignations to discharges set at 3 to 1. Of those who resigned, 26% did so because of illness, 19% were to move to another location (which could be a lot of things), 13% cited poor working conditions, 13% said there was an illness in the family, 14% had got another job somewhere else, 7% cited the poor living conditions, 6% got drafted or otherwise joined the military, and 2% complained about wages. Of those who were discharged, about a quarter of the time it was because they were an “unsatisfactory worker,” and the rest of the time it was because of chronic absenteeism. For construction at Oak Ridge, the average turnover rate was 17%, with mostly the same reasons given, though the resignations to discharge ratio was 2 to 1. (More people, by percentage, complained about the living conditions at Oak Ridge than at Hanford.) For the operations at Oak Ridge, the turnover rate was 6.6%, with a resignations to discharge ration of 1.3 to 1 — of those who left, a little over 40% did so because they were fired.

A 1944 "Stay on the job" rally at J.A. Jones Construction Co. in Oak Ridge. The workers seem a little unimpressed. Source.

A 1944 “Stay on the job” rally at J.A. Jones Construction Co. in Oak Ridge. The workers seem a little unimpressed. Source.

Of course, these numbers run through the entire tenure of the Manhattan Engineer District. When most people want to know how many people it took to make the bomb, they want to know up until August 1945 or so. I don’t have exact numbers on this. However, if we take the data from the report and the graphs, and assume an average monthly turnover rate of about 17% for the entire project, we end up with about the right number total.2 Subtracting all of the people added after August 1945, we get around 485,000 total people required to make the bombs during World War II. Given how much of that employment was front-loaded (again, with a peak in June 1944), I don’t think it’s too far off to assume that probably half a million people were employed to make the bomb. Which, to put that in perspective, means that during World War II, approximately 0.4% of all Americans worked on the bomb project — about one out of every 250 people in the country at the time.

Which is pretty impressive. By contrast, I’ve seen estimates that said that the Soviets used about 600,000 people total to make their atomic bomb. Which is not too different a number, actually — a bit less impressive than one might think if one is only comparing it to the peak of the Manhattan Project. The Soviets had around 170 million people at the time, so it works out to be a pretty similar percentage of the total population as the American project. Of course, one suspects that fewer of the Soviet workers were able to quit because they didn’t like the wage and working conditions. Though I’m sure they had their own form of grim “turnover.”

  1. Manhattan District History, Book I – General, Volume 8 – Personnel (dated 19 February 1946 but with numbers that suggest later additions were made. []
  2. If you want to play with the data yourself, I’ve uploaded it here as a CSV file. Some of it is extrapolated from the top graph. []

Little boxes of doom

Wednesday, October 23rd, 2013

I was at a (very interesting) conference last week and didn’t get a chance to do a regular blog post. I’ll have a real post on Friday, as usual, but I thought in the meantime people might enjoy this little passage I came across in William L. Laurence’s Dawn Over Zero: The Story of the Atomic Bomb (1946):

The secrecy frequently led to tragicomic situations. A trusted courier was dispatched by automobile to deliver a small box of material, the nature of which he was not told, to a certain locality several hundred miles away. He was cautioned that at the first sign of any unusual behavior inside the box he was to abandon the automobile in a hurry and run as far away from it as his legs would carry him.

The magnesium box used for transporting the plutonium core to the Trinity site. Via Los Alamos.

The magnesium box used for transporting the plutonium core to the Trinity site. Via Los Alamos.

Our courier asked no questions and went his way, taking frequent glances at the strange box behind him. Things went well until he came to the middle of a long bridge. Suddenly, from directly behind him, came a terrific boom. Out of the car he dashed like one possessed, running faster than he had ever run in his life. Out of breath and exhausted, he stopped to examine himself to make sure that he was still in one piece. Meantime a long line of traffic had gathered behind his driverless car and the air was filled with the loud tooting of impatient motorists.

Slowly he made his way back to his automobile and found to his amazement that it was still all there. Peering cautiously inside, he was even more amazed to find his precious box on the same spot as before. He was used to strange things, this courier, so he took his place at the wheel and was about the continue on his mission when once again he heard a loud boom directly behind him.

Once again he made a dash for his life, heedless of the angry horns that by this time were sounding from a line more than a mile long. Still exhausted from his previous mad dash, he nevertheless managed to put a considerable distance between himself and his mysterious box.

Eventually he made his way back, to find his car and his box in the same spot where he had left them. This time, however, he found an irate traffic officer waiting for him. Beyond showing the officer by his credentials that he was a Government employee, there was nothing he could tell him. It turned out that there had been blasting going on underneath the bridge.

Who knows how much of the story is true and how much of it is embellished by either Laurence or the original teller, but I thought it was highly amusing. One suspects, by the description of the box, the particular safety concerns, and the distance, that they are talking about the movement of the Trinity core from Los Alamos to the Trinity site.

John Coster-Mullen, in his fantastically interesting Atom Bombs (a newly-updated copy of which he recently sent me), has a somewhat related anecdote from the plane that transported the Fat Man core to Tinian in late July 1945: “During the flight to Tinian, they ran into a storm. [Raemer] Schreiber was sitting in the co-pilot’s seat and one of the guards came forward and tapped him nervously on the shoulder. ‘Sir, your box is bouncing around back there and we’re scared to touch it.’ Schreiber went back, corralled it, got a piece of rope and tied it to one of the legs of the cots.”