News and Notes

New book: The Most Awful Responsibility

by Alex Wellerstein, published December 9th, 2025

This is just a brief post to make sure I have announced on here formally that my new book from HarperCollins is now on sale!

Cover of The Most Awful Responsibility by Alex Wellerstein

The Most Awful Responsibility: Truman and the Secret Struggle for Control of the Atomic Age (HarperCollins, 2025) is a new and provocative and possibly controversial take on Harry Truman and his role in US atomic policy, from Hiroshima through the Korean War (and everything in between). The research for it took well over a decade, and some of the things I’ve previously written about on this blog regarding Truman have been part of that process. But the book pulls together quite a lot of new source material, new interpretations, and covers a much wider scope than I’ve posted on here. So if you’re interested in these kinds of things — or have someone in your life who might be — check it out!

I’ve written up more about the argument of the book on my other blog, Doomsday Machines, which I will just link to here:

The Most Awful Responsibility

And if you’re not already a free subscriber to Doomsday Machines… why not? What more do you want, mermaids?

OK — that’s all for now! Thank you for your interest, attention, tolerance, support, et cetera!

Redactions

Manhattan Project fissile material inventories

by Alex Wellerstein, published October 10th, 2025

Understanding how much fissile material — enriched uranium and separated plutonium — was produced, and at what time, by the Manhattan Project is one of those seemingly-obscure technical questions that comes with a lot of important historical implications. It is what determined the scheduling of the bombings, for one thing. For another, it is how you might answer questions about what would happen if the war had carried on. And for yet another, it is a way to debunk the various conspiracy theories that periodically emerge about either the United States having atomic bombs before July-August 1945, or being dependent on German uranium, or what have you.

Unfortunately for us, information that relates to the production rates of fissile material was considered among the most secret nuclear information in the postwar and Cold War period, because from that kind of information you can estimate stockpile production capabilities and limitations. So even in a secret project, this kind of data has historically been kept even more secret than the rest of it.

The late John Coster-Mullen wrote that this photo shows: “These are the three lead-lined steel cases used to transport the six U-235 target insert discs that arrived on Tinian August 28 and 29 [1945]. Each case contained two discs. The scientist is shown securing the lids.” He lists the source as Los Alamos National Laboratory.

The Manhattan District History, General Leslie Groves’ secret, official history of the Manhattan Project, contained this information in two different “Top Secret Appendices.” I’ll handle them both separately since one is very straightforward and the other is not.

Enriched uranium

The one for uranium stockpiles is part of the book on the electromagnetic enrichment method, as the Y-12 Calutron plant was the final step in the enrichment process before the material was sent to Los Alamos. When the Department of Energy released a major declassification of the MDH in 2014, they failed to release a version of the appendix volume. The volume was, however, included as part of the 1977 microfilm release of the MDH. 

Cumulative Shipments of U-235 from Electromagnetic Plant to Los Alamos, 1944-1946

“Cumulative Shipments of U-235 from Electromagnetic Plant to Los Alamos, 1944-1946.”

The graph above is a cleaned up version of the graph that is included in the relevant volume of the MDH (Book 5, Volume 6, “Electromagnetic Operation: Top Secret Appendix”), with the background grid reduced in intensity, in order  to make it easier to read the data.

It’s an interesting graph, but it doesn’t exactly read itself. Looking at it closely, and the numbers included in the relevant volume, it is clear that they are being very literal about “U-235” here: this only measures the actual content of U-235 in the shipments, not the total uranium. As the uranium shipped at different times had different levels of enrichment, the actual total amount of enriched uranium on-hand is a bit different than what the graph suggests. Which is somewhat clear when one notes that at the point marked “Hiroshima” on the map, they had only shipped a bit more than 50 kg, when the Hiroshima bomb itself contained 64 kg of uranium (~80% enriched), and had been sent from Los Alamos to Tinian some time before the operation took place. 

Here is a table I made which better indicates the details of the uranium production, based on the data in the volume and a little bit of math.

Date U-235 (kg) Enrichment HEU (kg) Rate (HEU g/day) LB Bomb Equiv.
10/7/44 1.7 67.5% 2.6   0.04
10/21/44 2.3 68.9% 3.3 52.8 0.05
10/28/44 2.6 69.3% 3.7 58.2 0.06
11/19/44 3.8 70.6% 5.4 76.8 0.08
3/4/45 20.4 77.2% 26.4 199.9 0.41
3/25/45 24.9 78.1% 31.9 261.6 0.50
4/22/45 30.5 79.0% 38.7 241.2 0.60
5/20/45 35.6 79.9% 44.6 212.3 0.70
7/17/45 52.5 81.6% 64.3 340.4 1.00
8/12/45 66.7 82.6% 80.8 632.5 1.26
9/9/45 88.2 84.5% 104.4 842.4 1.63
12/2/45 182.1 88.9% 204.9 1,196.5 3.19
12/30/45 231.4 90.1% 256.8 1,853.3 4.00
12/29/46 1,041.0 95.0% 1,095.8 2,305.0 17.08

Above, “U-235” refers to the total content of the isotope U-235 in the uranium sent — the same as the graph above. “Enrichment” is the percentage of U-235 in the material sent. It is a little unclear in the source whether this is “the uranium sent in the last batch” versus “the total average enrichment of all uranium sent to Los Alamos up until this point,” but I suspect they are pretty similar numbers either way. “HEU” is a derived value from the U-235 and the enrichment — how much actual enriched uranium metal had been shipped, regardless of the enrichment level. So this is the number that lets you see that they definitely had enough metal on hand for the Little Boy bomb (64 kg) to be dropped on Hiroshima in early August. “Rate” refers to what the production rate of HEU was, in grams per day, and is a nice way to see how the rate of production improved over time (just as the “Enrichment” column lets one see how much better they got at enriching it), as they further debugged their plants and more parts came online. Lastly, “LB Bomb Equiv.” is just a simple measurement of how many Little Boy bomb cores the HEU number represents — it is just that number divided by 64 kg.

My estimate, based on the above data, is that you don’t have enough HEU for a second Little Boy bomb until mid-September 1945. Which is only slightly relevant, since, if the war had gone on, they likely would have not made more Little Boy bombs, but instead would have made composite (uranium-235 + plutonium) implosion bombs. But it does impact the question of “what would the atomic bombing schedule have been like if they only had gun-type bombs” (about two months between each bomb). 

Plutonium

For plutonium, it gets more difficult. The relevant volume (Book 4, Volume 6, “Pile Project – X-10 – Top Secret Appendix”) was not included in the 1977 release, but was partially included in the 2014 release. The relevant graph, though, was totally redacted:

A totally redacted page from the Manhattan District History, with a DELETED stamp repeatedly put across a blank piece of paper that is obscuring the content underneath

So that’s the end of the story, right? This is a graph too spicy for people like you and me, right? Right? As people of my generation used to say: “As if.”

I have to admit, when I see something like this — data that I don’t feel has any legitimate reason to be classified, and would be interesting/useful for my historical study — I take it as a bit of a challenge. I take it personal, you could say. 

Now, I happen to know that parts of the MDH have been declassified and scattered across various databases and archives. Depending on who reviewed it, and when they did so, their interpretations of what could be released varied. So if one can locate multiple versions of its sections, one can sometimes reconstruct a “master” version with more content than any individual one. This is what the version of the MDH that I have uploaded to Archive.org (linked to in this post) is, and I have been doing this over the last ten years as I come across multiple copies. 

The little insight I had in this case was that there might be copies of the MDH in the Hanford DDRS database, which has been at a strange URL for a while now. And… I was right! There are actually two different copies of the relevant volume in there, and they both include the “plutonium production” graph, from a release of these volumes back in 1991. The only problem is that they are terrible microfilm scans, and so are barely legible. The best one (document D8719897) is this one:

A very hard to read graph of plutonium production

“Plutonium Production.” But a bit hard to read.

One can, at least, see the relevant lines. But what are they of? What is the scale? Better than nothing, but it “reads itself” even less than the uranium graph. There’s no bit depth there; it’s essentially all black and all white, so there’s no hope of drawing out the missing data by playing with the contrast. 

Judging from other similar graphs in the file, the two lines are at different scales; one is “Scale x 1000” and the other is “Scale x 1,” and then when line “A” wraps around on the right, it becomes “Scale x 2000.”  So if the units for “B” are kilograms, that would make the units for “A” in tons. Or if “B” was grams, “A” would be kilograms. Other graphs in the file have pretty standard scales, with each “square” having a height of 10 (of whatever unit). In the above, the visible squares are really twice as high, so each horizontal line corresponds to 20 “units.” 

Here is the raw data, expressed just as “A” and “B”, with the scale differences applied, based on my pixel readings of the graph (so there is some error there). I am reading each “date” value as the rightmost value of the date range, as that seems to be where the person graphing them made changes to the slope:

Date Curve A Curve B
Dec-44 1,397.8 0.0
Jan-45 2,580.6 0.3
Feb-45 5,161.3 0.5
Mar-45 7,311.8 0.9
Apr-45 15,053.8 1.6
May-45 21,828.0 8.5
Jun-45 30,537.6 13.7
Jul-45 49,462.4 20.2
Aug-45 70,000.0 32.8
Sep-45 97,096.8 44.5
Oct-45 120,215.1 64.6
Nov-45 145,161.3 86.1
Dec-45 164,946.2 102.0
Jan-46 180,860.2 121.8
Feb-46 197,311.8 136.7
Mar-46 221,075.3 151.3
Apr-46 235,914.0 167.3
May-46 249,784.9 184.1
Jun-46 258,064.5 198.7
Jul-46 271,505.4 211.8
Aug-46 283,440.9 226.6
Sep-46 294,408.6 236.3
Oct-46 308,172.0 246.1
Nov-46 320,000.0 255.7
Dec-46 330,752.7 269.1
Jan-47 346,451.6 278.9
Feb-47 356,774.2 287.3
Mar-47 371,828.0 295.9
Apr-47 383,010.8 302.0

My pixel counts are based on an assumption of scale that translates to 1 pixel being about 1.2 of the units of value, which gives some sense of the error bars of this kind of eyeballing.

I have graphed the above data here (without the 1000X scale applied, but the 2000X area is plotted as 2X):

The replotted data from Curve A (blue) and Curve B (orange).

Which lets us think about what “A” and “B” most likely correspond to. Some observations:

  • The percentage of “A” that “B” is changes over the course of the graph. Starting in May 1945, “B” is some 40% to 80% of “A,” not taking into account the scale differences (0.04% to 0.08% if you do take them into account).
  • You could also read “B” as possibly being offset in time by “A”: whatever (unscaled) value of “A” repeats in “B” some several months later. The fact that “A” seems to be repeated (at 1000X less scale) in “B” after 30-50 days seems meaningful.
  • Both numbers only go up, and never go down, which suggests to me that they must be cumulative, since the actual rates of plutonium production fluctuated a bit over this time period. 
  • Curve A starts in December 1944, and Curve B starts potentially in January 1945 (but its value may be 0), definitely in February 1945. 

So my guess, based on other of plutonium production records kept at the time, is that Curve “A” is related to tons of irradiated uranium processed, and Curve “B” is kilograms of final “product” (separated plutonium) isolated.

We have some data points we can compare these assumptions to to check them. Another document in the Hanford database (says that in early 1947, Hanford shipped 9.2 kg of plutonium in January, 8.6 kg in February, 9.6 kg in March, and 8.6 kg in April.1 Our numbers for Curve B above, when rendered into a “rate of change” per month for those months in 1947, come out with 9.8, 8.4, 8.6, and 6.2 — all close-enough look plausible for Curve B.

Los Alamos produced several inventories of their plutonium in 1945 that have been at least partially declassified. I have one of these; the Center for Disease Control released a graph of 20 datapoints of plutonium as part of their Los Alamos Historical Document Retrieval and Assessment (LAHDRA) Project in 2010:2

“Cumulative amounts of plutonium received [by Los Alamos] from Hanford in 1945.”

They don’t provide the raw data (boo!) but using my pixel-picking method I basically came up with this:

Date Plutonium (kg)
4/18/45 0.7
4/25/45 0.7
5/2/45 1.1
5/9/45 1.6
5/16/45 3.1
5/23/45 4.5
5/30/45 6.4
6/6/45 7.4
6/13/45 8.8
6/20/45 10.1
6/27/45 12.5
7/4/45 13.8
7/11/45 16.2
7/18/45 16.2
7/25/45 17.1
8/1/45 18.7
8/8/45 22.1
8/15/45 24.3
8/22/45 27.6
8/29/45 27.6

Which seems about right. (The report I have, for 8/29/1945, has the total as 27.5 kg.)

If we put that graph up along with our graph for Curve B, we get this:

LAHDRA (blue dots) versus Curve B (orange).

Which is interesting. They both have basically the same slopes, but Curve B is definitely higher than the LAHDRA curve. 

I have basically two hypotheses about this. One is that Curve B is the mass of plutonium in a different form, like plutonium nitrate, that might be heavier than the isolated pure plutonium metal that Los Alamos might have been using. I’ve poked around with this a bit, but I’m not really that convinced that is the issue.

The other, which I currently favor, is that we’re really just seeing the difference between plutonium separated at Hanford (Curve B) and the time it took to send it to Los Alamos. So Curve B has a value of about 1.6 on 4/30/45, and the LAHDRA data has 1.6 on 5/9/1945. There are other such “correspondences”; in general, there is what looks like ~10 day delay between the two curves. A section in the MDH’s “Top Secret Appendix” says that the normal schedule was for, once a week, Hanford to pack “all the cans available for shipment” into wooden boxes and ship them by truck to Los Alamos in a modest convoy. The convoy itself took 36 hours to reach New Mexico. So 8-9 days or so. At which point it would need to be processed and then added to the Los Alamos inventory. So those numbers more or less add up.

All of which makes me think that “Curve B” is indeed plutonium produced at Hanford — which is not necessarily the same thing as the amount of plutonium that was on hand and ready to use Los Alamos.

So if that is correct, we can generalize Curve B’s data for plutonium produced by Hanford:

Date Plutonium (~kg) Rate (kg/Pu/mo.) FM equiv.
Dec-44 0.0   0.0
Jan-45 0.3 0.3 0.1
Feb-45 0.5 0.2 0.1
Mar-45 0.9 0.3 0.1
Apr-45 1.6 0.8 0.3
May-45 8.5 6.9 1.4
Jun-45 13.7 5.2 2.2
Jul-45 20.2 6.6 3.3
Aug-45 32.8 12.6 5.3
Sep-45 44.5 11.7 7.4
Oct-45 64.6 20.1 10.4
Nov-45 86.1 21.5 13.9
Dec-45 102.0 15.9 16.5
Jan-46 121.8 19.8 22.0
Feb-46 136.7 14.8 24.0
Mar-46 151.3 14.6 25.2
Apr-46 167.3 16.0 27.0
May-46 184.1 16.8 29.7
Jun-46 198.7 14.6 32.0
Jul-46 211.8 13.1 34.2
Aug-46 226.6 14.7 36.5
Sep-46 236.3 9.8 38.1
Oct-46 246.1 9.8 39.7
Nov-46 255.7 9.6 41.2
Dec-46 269.1 13.4 43.4
Jan-47 278.9 9.8 45.0
Feb-47 287.3 8.4 46.3
Mar-47 295.9 8.6 47.7
Apr-47 302.0 6.1 48.7

This data is much less accurate than the uranium graph, because I am eyeballing the graph values for each month. But it looks about right to me. The plutonium (kg) column is the eyeballed data — as you can see, it is not really very precise. The “rate” is the change in those values change per month. And “FM equiv.” is just assuming that each core for a Christy-type Fat Man bomb is 6.2 kg. It should be kept in mind for thinking about stockpiles that a) the US “expended” ~12 kg of plutonium in the July and August detonations, as well as another ~12 kg in the tests of Operation Crossroads in mid-1946, and b) that any stockpile assumptions are complicated by the fact that after World War II, the US was also developing composite cores, as mentioned before, which did not use the same amounts of plutonium as the original “Fat Man” bombs.

One thing that jumps out from all of the data above is how different the production rates were between the uranium and plutonium methods. The uranium method just got better and better, in terms of quantity and quality (enrichment level). But the plutonium production rates bounce around a lot more. This is unsurprising, knowing the history — they had severe problems at Hanford with the reactors in the postwar, and even shut down B Reactor in March 1946 so as to preserve its longevity. 

Bringing it all together

We can somewhat haphazardly combine our two datasets now into one master graph for fissile material production by the Manhattan Engineer District:

Fissile material production (highly-enriched uranium and separated plutonium, both in kilograms) by the Manhattan Engineer District, 1944-1947.

I have thrown out the plutonium production for early 1947, just because that was under the Atomic Energy Commission, and because we don’t have the enriched uranium data to go alongside it. We can see two things here. One is that when plotted against the same axis, the dramatic differences in production rates are really apparent. One can readily see why the postwar Manhattan District, and the early AEC, took the issue of plutonium scarcity and uranium abundance so seriously, and why they were very invested in developing composite cores that could allow them to “stretch” their much more constrained plutonium supply further. 

To break this into something very “practical,” we can think about these as “weapon equivalent amounts.” Here is a little graph I have been playing with, which maps both the Little Boy equivalents of HEU (64 kg each) and the Fat Man equivalents of plutonium (6.2 kg each), as well as various speculative “composite core” quantities of plutonium and HEU mixtures:

Weapon equivalents of fissile materials 1944-1947. For “composite” cores, it assumes a 50:50 mixture of each (e.g. 2 kg Pu + 2 kg HEU).

Chuck Hansen suggests that the composite cores tested in 1948 “probably contained about two to two-and-a-half kilograms of plutonium; in addition to this amount of plutonium, each composite bomb core also contained a comparable amount of uranium.” In the above, it turns out to be entirely dependent on how much plutonium you assume, because the HEU quantities are generally in such excess of the plutonium that you can treat them as essentially unlimited except in cases where the plutonium content is low (e.g. 2 kg) and the HEU content is high (e.g. 8 kg). Anyway, this graph is just one example of what you can “do” with this data: to show how the fissile material supplies are intertwined with questions of possible stockpile size, and how certain design choices affect those outcomes. 

What a lot of effort to reconstruct a rather unsurprising (but still interesting) graph of data from some 80 years ago! I cannot see how any of the above could have compromised national security in any way. But I will further note that all of the above was accomplished on the basis of records that the US government actually already judged, in the past, as being declassifiable. So if somehow it did compromise national security in some nebulous way, the fault is on the redactors in either 1977 or 1991 who decided — I think quite correctly — that it was innocuous data. 

  1. SF Materials Shipped or Received from 12/31/1946 thru 05/01/1947,” (May 12, 1947), Hanford DDRS access number D8265435. See also this cover letter for a little more context. []
  2. Center for Disease Control, Final report of the Los Alamos Historical Document Retrieval and Assessment (LAHDRA) Project (November 2010), chapter 4, page 5. []
News and Notes

News and updates

by Alex Wellerstein, published September 29th, 2025

I realized I haven’t updated things here for a long while, and that it would be worth consolidating a few overdue news updates.

First and foremost, if you want to read things from me on a more regular basis, you should be reading Doomsday Machines, which is another blog of mine, and is much more frequently updated that this one. While it is not exactly the same content or approach, you’ll find a lot of things from this blog replicated on there. Because the same person writes both of them. (I still intend to update this blog occasionally, but one only has so much time.)

Cover art for Alex Wellerstein's The Most Awful Responsibility: Truman and the Secret Struggle for Control of the Atomic Age

Second, I have a new book coming out in December 2025 from HarperCollins: The Most Awful Responsibility: Truman and the Secret Struggle for Control of the Atomic Age. You can think of it as a sort of “atomic biography” of Harry Truman, with about half of the book focused on the use of the atomic bombs during World War II, and the rest about the non-use of atomic bombs during the rest of his administration. My basic argument is that Truman was, somewhat surprisingly, one of the most anti-nuclear presidents of the 20th century. In other words, it is provocative, but extensively researched. Keep an eye out! And if you’re the kind of person who hosts a podcast or book clubs or book talks or whatever, feel free to get in touch. 

Third, and last, for at least 2025-2026 I am living in Paris, France. I am currently a visiting researcher at the Nuclear Knowledges group, at the Center for International Studies, in Sciences Po, working with the wonderful Benoît Pelopidas. I am still an associate professor at Stevens (I am on leave). I’ve been here about a month. I’m just putting this out there because it takes time for news to diffuse, and also to let anyone in Europe know (who might, say, want me to give a book talk) that I’m in your orbit. And yes, Lyndon, my dear old dog, has come with us, and is enjoying it quite a lot. 

OK, that’s all for now! I am busy with a number of projects. Again, if you want more regular posts, subscribe to Doomsday Machines, which is free. If you want to learn more about what I’m doing from week to week (or just support me, or just get more photos of the dog), you can also sign up for the paid subscription, but it is absolutely not required!

Redactions

Did Sandia use a thermonuclear secondary in a product logo?

by Alex Wellerstein, published September 4th, 2024

I happened to look at a slide deck from Sandia National Laboratories from 2007 that someone had posted on Reddit late last night (you know, as one does, instead of sleeping), and one particular slide jumped out at me: 

It’s a little graphic advertising the different kinds of modeling software that are part of something called the SIERRA framework, as part of a pretty standard “overview” presentation on computer modeling at Sandia that was given at a meeting in Luxembourg.1

Did you catch the part that made me stop and audibly say, “uhhhhh“? Look at the lower right:

So, that looks an awful lot like the cutaway of a compact thermonuclear weapon design. I immediately wondered if I couldn’t find a better resolution version of the same graphic, so I went onto OSTI.gov and starting plugging in terms that seemed relevant. Searching for “Sierra” and “Salinas” and restricting to “Conference presentations” turned up a bunch of other instances of it from the 2007-2011 or so timeframe. The one with the highest resolution came from another presentation, from 2008:2

So this is awfully strange. We’ve got something here that looks like a plausible reentry vehicle for a nuclear warhead. The bits in red, yellow, perhaps fuscia at the “tip” are in the position (and about the right size) to be the arming, fuzing, and firing system. The bits below that — the green, the blue, etc. — look like a thermonuclear warhead. The green part looks like it is meant to represent the location of the “primary,” while the the cylinders-within-cylinders are a classic representation of a thermonuclear “secondary.” One could debate about the exact identity of each color, but it looks a lot like it is meant to represent a radiation case, an interstage medium, a tamper, fusion fuel, and a “sparkplug.” You’ve even got an interesting little “dip” into the central cylinder which looks like a channel to get neutrons into the “sparkplug.” 

By comparison, this image from later in the presentation looks a lot more like what one would expect them to release about a reentry vehicle in a public document — just the arming, fuzing, and firing system (the top part, with the detail at right), and then the “warhead” section depicted as a featureless blank:

Even that is a little more revealing than usual, as it gives pretty precise dimensions. So seeing something that looks like it is meant to represent the warhead itself is… pretty surprising!3

This isn’t some one-off slip up kind of thing. This particular graphic is present in at least half-a-dozen conference presentations on OSTI.gov, and even some on a few other government websites (like this presentation given to NASA). It’s literally the logo they use for this particular software package. And it’s not some kind of redaction error, like the ones I wrote about previously, in which things not dissimilar from the above were very clearly intended to be redacted, but were done so poorly that you could in fact see some aspects of them. This is literally the logo for this particular software framework, and it has been used in lots of presentations (including those done overseas), and is posted all over unclassified, public-facing databases hosted by the federal government.

It took me a little more searching, but I eventually tracked down an isolated version of the image from yet another Sandia presentation:

The slide doesn’t give any clarification as to what we’re looking at, here, other than indicating that it part of modeling work for the purposes of structural dynamics, and is clearly part of a nuclear weapons context.4

The SIERRA software framework, I gather, is a simulation/modeling toolkit that allowed scientists to basically simulate a relatively “full spectrum” of weapons safety issues. This is Sandia’s bread and butter: making sure that your weapon won’t go off if, say, you drop it, or set it on fire, or let it get hit by lightning. Things which have happened a number of times over the years.5 The “Salinas” package in particular seems to be about modeling mechanical aspects of materials. Which is to say, this demonstration of its “capabilities” is not about showing you that it is modeling how a nuclear weapon would detonate. It is showing you, “look, we can model a lot of different materials — steel, uranium, lithium, etc. — and could probably tell you whether they would crack or strain or shatter or whatever if you, say, dropped this weapon.” That’s my quick gloss on the various presentations, anyway.

To give a sense of how strange this is, here is the only “officially sanctioned” way to represent a multistage thermonuclear weapon, according to US Department of Energy guidance since the 1990s:

Figure 13.9, “Unclassified Illustration of a Staged Weapon
(Source: TCG-NAS-2, March 1997),” from the Nuclear Matters Handbook 2020 (Revised), published by Deputy Assistant Secretary of Defense for Nuclear Matters.

Two circles in a box, maybe inside of a reentry vehicle. That’s it. Nothing that gives any actual sense of size, location, materials, physicality. One can compare this with the images of more speculative thermonuclear weapon designs in the public domain for a sense of how limited the official release is compared with what is “believed to be known” about such things:

Somewhat speculative diagram of a W88 nuclear weapon, from Dan Stober and Ian Hoffman, A Convenient Spy: Wen Ho Lee and the Politics of Nuclear Espionage (Simon & Schuster, 2001), via Howard Morland.

Incidentally, I submitted a FOIA request on that particular guidance document (TCG-NAS-2) some time back, and the document that I got back was hilariously redacted to the point that even terms like “gun-type” and “implosion” were redacted, much less any and all images, despite that document apparently containing examples of what actually could be said publicly about these things.6 Which is just to emphasize, it’s not like the DOE is particularly loose about even as vaguely representational an image as is that one — if anything, the err in the other direction. 

Why are they so uptight about thermonuclear weapon design “shapes”? The official reason, of course, is because of proliferation concerns. But there’s another reason: even the appearance of giving away “secrets” can generate unwanted publicity and political scandal. 

In 1999, the Cox Committee’s report on Chinese nuclear espionage made some hay out of publicly-available depictions of H-bombs, and featured an entire spread dedicated to the fact that “visitors to Los Alamos National Laboratory are provided a 72-page publication that provides, among other things, a primer on the design of thermonuclear weapons.” It sensationalized that very two-circles-in-a-box image that I showed above, and weaponized it. How dare Los Alamos give that away! Despite it being unclassified. But that’s what I mean by unwanted political scandal — lots of scandals about the release of “secrets” involve non-secrets. (There’s a lot on this sort of thing in my book, of course.)

Which leads us to an interesting puzzle: why would the censors repeatedly allow Sandia to use what appears to be a thermonuclear weapon cutaway as part of a promotional diagram for a software package? There are a few possibilities that come to my mind.

I gave a talk at Sandia this summer, and they made me wear this badge (and another one with my face on it, which I wasn’t allowed to photograph or keep) everywhere I went. Presumably so nobody would tell me secrets, but also, perhaps, to indicate my willingness to play Checkers.

One is the idea that this is an accident, a leak, an oopsie. I find this unlikely to the point of near impossibility. Not because the classification officers are perfect. But this is so obviously not something you would authorize for release if you thought it was representing something classified. To have approved many presentations with this graphic in it to go out into the world, to be posted on the websites of multiple government agencies… they’re not perfect, but they’re not fools. Again, if anything, they tend to err on the side not releasing enough. So I find it hard to believe that they’d have messed this up, again and again, when it is the most blatant thing in the world. This isn’t some subtle technical thing. Anyone who thinks about weapons information and secrecy is going to know what a cylindrical secondary looks like. I mean, this thing jumps off the page if you are that kind of person. Which I am, of course, but so are redactors. If this were the case, it would be an incredible and repeat failure of the classification system at many points, in the same way, over several years. One can’t say such a thing is impossible but I find that extremely unlikely.

Another easily dismissible possibility is that this is some kind of deliberate release of classified information. Again, there is an entire infrastructure devoted to not letting this happen. With peoples’ jobs, security clearances, and personal freedoms on the line. Plus the fact that the people who tend to work in these jobs take for granted that secrecy translates to security. Even actual spies wouldn’t do it this way — they’re not about releasing secrets to the public, they’re about channeling them to the people they are spying to, quiet-like. 

So we’re left with much more plausible conclusion that they consider this to be unclassifiable and benign. But why would they think that, given what we know about how sensitive they are to anything that comes even remotely close to representing internal weapon components? 

This “multipurpose test object” (taken from the aforementioned TGC-NAS-2 report from 1997) is an example of what I mean by a deliberately “unclassified shape”: something specified by the DOE as being evocative of the kinds of physical shapes and materials that are involved in nuclear weapons designs, but are explicitly indicated as being not actually relevant to weapons design. So this kind of “shape” is something you could use to validate simulation codes on which would probably work with actual weapons materials/designs, but would not actually reveal any weapons materials/designs information other than what has already been declassified.

The “obvious” answer, if my above assertions are true, is that it must not actually represent a thermonuclear secondary. What else could it be? It could be some kind of pre-approved “unclassified shape” which is used for diagnostics and model verification, for example. There are other examples of this kind of thing that the labs have used over time. That is entirely a possibility. What would be bizarre about this being the answer is that a) “unclassified shapes” generally don’t look like actual, plausible weapon designs, and this thing looks “close-enough”; b) it still gives off the appearance of a classified shape, which as noted, is dangerous in and of itself from a political standpoint; and c) if the goal is just to show off modeling capabilities in a very superficial way (this is essentially an advertising logo) they surely could have picked a million less provocative (from a classification standpoint) examples. 

It’s also possible that it isn’t even meant to be a nuclear weapon at all. Sure, it looks like a reentry vehicle. Yeah… it seems awfully nuke-shaped. But there are other things that can look like nukes but at really meant to be something else. Maybe I’m seeing a “secondary” because I’m primed to see one, by the context? It’s… possible. Neither spheres-within-sphere nor cylinders-within-cylinders are inherently related to nuclear weapons components. But when you place them like that, in a reentry vehicle, in that order… it looks very much like a fusing system, a primary, a secondary… It would be quite surprising to me if it was not meant to be representative of those things, but something totally different. And, again, the original context of that model appears to be very firmly rooted in nuclear weapons development.7

Another possibility is that it is some kind of “deliberate disinformation” or “misinformation.” This is the kind of thing that I think people assume the government labs might do, but in my experience, is pretty unusual and pretty unlikely. In general, you have to remember that the national laboratories are pretty, well, boring, when it comes to classified information. They want to be boring in this respect. They are not doing cloak-and-dagger stuff on the regular. They’re scientists and engineers for the most part. These are not James Bond-wannabes. They don’t parachute behind enemy lines to set up palace coups. They are extremely rule-abiding for the most part. There are lots of social and historical reasons for this (again, my book goes into the historical ones — the anxiety about “nuclear secrets” always made the Atomic Energy Commission and its successor organizations very anxious about being accused of being lax about them). 

And beyond the institutional culture aspects, the idea that a bunch of engineers at Sandia are going to be using a software package logo to deliberate leak out misinformation, just waiting for someone to notice it, seems a little unlikely to me on the face of it. I mean, really. What is the “operation” here? Who is meant to be “fooled”? Me? You? The North  Koreans? It doesn’t feel very realistic.8

And one can add to the above the fact that, at least historically, the Atomic Energy Commission and its successor organizations have frowned on disinformation and misinformation for other very practical reasons. If you release a lie, you run the risk of someone noticing it is a lie, which can draw more attention to the reality. And even misinformation/inaccuracy can put “brackets” around the possibilities of truth. The goal of these organizations is to leave a total blank in the areas that they don’t want people to know about, and misinformation/disinformation/inaccuracy is something other than a total blank

That’s where I’ve ended up, in thinking about what this “means” and what possibly accounts for it. But it’s still bizarre that anyone would allow something that looks so suggestive, even if it is not accurate, to be released as an official product of a national laboratory. It seems like a bad idea, anyway. And yet — I can’t come up with an explanation for this that isn’t one kind of bad idea or another. But I think this is the “most plausible bad idea” of the set.

One last thing. In more recent presentations on the SIERRA Mechanics framework, they changed the diagram somewhat:9

The resolution isn’t great, but you can see that the potentially problematic part is much more obscured. But it’s still there, so I don’t think that is really an attempt to draw attention from it, so much as it is an artifact of somewhat careless graphic design. In general, it’s not a great logo by any means — too busy, too complicated, too much information, does not reproduce well at small sizes or low resolutions, etc. — but, as discussed, that is not even close to the most potentially problematic aspect of it!

I saw this and couldn’t resist quickly writing something up about it. That’s all I’ve got. If you’ve got thoughts on it, let me know. And if you haven’t already signed up for it, I am much more active on my other blog, Doomsday Machines, as of late!


I’ve updated this post a few times since I first put it up this afternoon, but just stumbled across something even more helpful. Here’s an image from a 2014 article about computational science at Sandia that looks awfully similar to the one above:10

Unlike the others, it comes with a caption: “The multiple components of a nuclear weapon body are highlighted in this intentionally simplified mesh. Each part is comprised of numerous subcomponents, fastened together with screws, nuts, bolts, jar-lid-like fittings and more.” Which is just to say, it is pretty clearly saying that this “thing” is meant to be some kind of representation of a nuclear weapon, albeit “intentionally simplified.” Which doesn’t really solve the mystery — if anything, it just highlights why I still find it so odd that this thing got approved for released at all! Not in the sense that it contains “secrets” — but in the sense that it is just not the kind of image the national labs tend to release. 

Someone reminded me of something I had seen years ago: the British nuclear program at Aldermaston, when it has published on its own computer modeling in the past, used a sort of “bomb mockup” that looks far more deliberately “fake” than this Sandia one. I offer this up as what I would think is a more  “safe”  approach than something that looks, even superficially, like a “real” secondary design:

This is called the MACE (Modal Analysis Correlation Exercise) assembly, and was created by the UK Atomic Weapons Research Establishment in the 1990s to serve as a sort of a Utah Teapot of weapons structural modeling: a benign shape that could be used to test aspects of the code that would nonetheless tell you if the code would work for real weapons assemblies.11

Anyway, I’m just surprised the DOE would release any image that gave really any implied graphical structure of a thermonuclear secondary, even if it is clearly schematic and meant to be only somewhat representative. It’s more than they usually allow!

  1. Harold Morgan, “Sandia National Laboratories and Engineering Sciences Overview,” SAND2007-6636P, Presentation to Goodyear/Sandia CRADA Meeting Colmar-Berg, Luxembourg (22 October 2007). []
  2. Heidi Ammerlahn, Richard Griffith, and Paul Nielan, “Modeling and Simulation at Sandia: An Overview,” SAND2008-3315P (23 April 2008). []
  3. And, just to be very clear about it, that complicated set of machinery in the render is the arming, fuzing, and firing (AFF) system. The basic shapes of such systems have been declassified for a long time. It is the system that causes the warhead firing signal to be sent if the right conditions are met. It is not the warhead itself and is a separate component. []
  4. Thomas M. Baca, “1523 General Capability Overview,” SAND2007-6128P (1 September 2007). []
  5. Sandia made (and has since put online) a very informative, well-produced, three-part documentary about their work on the technical side of “command and control” of nuclear weapons, titled Always/Never: The Quest for Safety, Control, and Survivability. It’s worth a watch if you haven’t seen it. Separately, one of my favorite bits of weapons jargon is the term “mechanical insult,” which means denting your warhead in some way. []
  6. U.S. Department of Energy, “Joint DOE/DoD Topical Classification Guide for Nuclear Assembly Systems,” TCG-NAS-2 (March 1997), received in 2021 in response to FOIA request HQ-2020-00067-F. []
  7. For example, I don’t know exactly what this is meant to be — an example used in a Los Alamos presentation on computer modeling — but it’s not a nuclear weapon. []
  8. And nor does taking it one level “deeper”: the idea that they’d put out real information to make us think it must be fake information, because why else would they put it out? This is an amusing idea but, I assure you, is not how bureaucrats think, and we are talking, for better or worse, about bureaucrats here. []
  9. E.g., Timothy Walsh, Greg Bunting, Andrew Kurzawski, Ellen Le, and Kevin Dowding, “Large-Scale Inverse Capabilities in Sierra Mechanics,” SAND2019-6059C (May 29, 2019). []
  10. Monte Basgall, “Joint venture,” DEIXIS Magazine (September 2014). []
  11. Some more info on the MACE assembly can be found in this PhD thesis from 2004: Philip Ind, “The Non-Intrusive Model Testing of Delicate and Critical Structures” (Imperial College of Science, Technology, and Medicine, University of London, 2004). The screen cap image comes from an in-house AWRE publication (Discovery) from 2000. []
News and Notes

Announcing DOOMSDAY MACHINES

by Alex Wellerstein, published July 12th, 2024

I have been busy this summer (and spring, and the winter before that… and the fall before that… and the summer before that…), but one of the things I’ve been busy with has finally launched: Doomsday Machines, a new blog dedicated to exploring the post-apocalyptic imagination from several different perspectives. It will include discussions of post-apocalyptic media, documents that shed light on how governments thought and think about the end of the world, and explorations of the task of creating practical “models” for what the end of the world could look like. Among other exciting things.

The Doomsday Machines banner.

If you’re interested in checking out what it is, head over to https://doomsdaymachines.net/. The “Welcome to Doomsday Machines” post that I put up today lays out what it is going to be all about. It is a very different sort of endeavor than what I am doing on this blog, but hopefully will be seen as a complement to it. And if you’re a fan of my writing on here, you probably will enjoy Doomsday Machines, as it involves a lot of the same kind of topics, albeit in somewhat shorter (and more frequent) posts.

Restricted Data will continue (as much as it has been, anyway) to be a place for me to post more serious thoughts about nuclear history in general. I have recently changed its subtitle from The Nuclear Secrecy Blog to A Nuclear History Blog, because its scope arguably has always gone beyond that of just nuclear secrecy. 

I’m well-behind on updating Restricted Data for awhile now — I have several things I would like to write-up and post here, and who knows, I might be able to find some time soon to do it. But I’ve been really tied up with other projects right now, including Doomsday Machines, but also the next book, the video game project, and some other software I received a grant to work on. My sabbatical has been an extremely busy one, to the extent that I’m somewhat looking forward to the regularity that comes with teaching when I start up again this fall. 

Anyway — I just wanted to post something about Doomsday Machines, and the future of this blog, here. More forthcoming!