Jeffrey LewisHitlers Bombe Won't Go Away

Rainer Karlsch, author of Hitler’s Bombe, reveals “a previously unpublished diagram of a German nuclear weapon”:

Shortly after the end of the war in Europe, an unknown German or Austrian scientist wrote a report that describes work on nuclear weapons during the war. This report, which RK discovered after Hitlers Bombe was published, contains both accurate information and less accurate speculation about nuclear weapons, and may well include some information from the Manhattan Project – the word “plutonium” is used, for example. Unfortunately, the title page is not included and there is no other evidence of who composed it. However, this individual does not appear to have been a member of either the mainstream German uranium project or the group working under Diebner.

What the report does demonstrate is that the knowledge that uranium could be used to make powerful new weapons was fairly widespread in the German technical community during the war, and it contains the only known German diagram of a nuclear weapon (figure 2). This diagram is schematic and is far removed from a practical blueprint for an “atomic bomb”.

The diagram appears in a Physics World article co-authored by Union College historian Mark Walker.

The BBC notes the report appears to have drawn on the official history of the Manhattan Project by Henry De Wolf Smyth, entitled Atomic Energy for Military Purposes: The Official Report on the Development of the Atomic Bomb Under the Auspices of the United States Government (The Smyth Report). That report revealed the word “plutonium” (coined under wartime secrecy of the Manhattan Project) and the concept of a “tamper” to reduce the critical mass necessary for a chain reaction—both appear in the report discovered by Karlsch.

Karlsch and Walker note the estimate of a critical mass of slightly more than 5 kg for a plutonium bomb could not have been derived from the Smyth Report because “such detailed information was not included in the Smyth report.”

Maybe I am missing something here, but the Smyth Report does explain the role of tampers in Chapter XII:

In a uranium-graphite chain-reacting pile the critical size may be considerably reduced by surrounding the pile with a layer of graphite, since such an envelope “reflects” many neu-trons back into the pile. A similar envelope can be used to reduce the critical size of the bomb, but here the envelope has an addi-tional role: its very inertia delays the expansion of the reacting material. For this reason such an envelope is often called a tamper. Use of a tamper clearly makes for a longer lasting, more energetic, and more efficient explosion. The most effective tamper is the one having the highest density; high tensile strength turns out to be unimportant. It is a fortunate coincidence that mate-rials of high density are also excellent as reflectors of neutrons.

It seems to me the drawing is not really all that revealing.

The one interesting thing—to me at least—is that the design looks like a gun-type assembly using plutonium, which is infeasible. But I don’t read German and the image is fuzzy.


  1. Andrew Gray (History)

    The appearance of the word “plutonium” is interesting; at first glance, since the word had been coined in secrecy in the US, it’d seem to indicate this was made with knowledge of (some) Manhattan Project material.

    But it transpires that both British and American research groups, working in isolation, had theorised about and named elements 93 and 94 as “Neptunium” and “Plutonium” – because they were the logical successors to 92, “Uranium”. This would be by, oh, ‘40; well before anyone had created any.

    It’s logical to assume that their equally cultured German counterparts, on thinking of transuranic elements, would name them in the same way.

    I don’t really have an opinion over whether the report is genuine (though I await the next Physics World with interest); given the profusion of futile German secret programs in 1944/5, a reasonably competent study of a plutonium weapon is perfectly plausible… but not evidence for much more than a study, Karlsch’s theories aside.

  2. Cheryl Rofer (History)

    I’m wondering about the provenance of the report and its authenticity.

    >Unfortunately, the title page is not included and there is no other evidence of who composed it.<

    Um yeah, right. This sort of thing could make one suspicious.

    The component names are typically German compounds. Insofar as I can read the blurry type and work through my limited German, they seem to be varieties of walls, jackets, and masks. Not too informative, but this could be consistent with wartime secrecy. After all, Los Alamos was assembling a “gadget.”

    And there is no label on the upper red component, which I assume is part of why Jeffrey sees this as a gun design. That’s the one I’d like to see called out.

  3. Cheryl Rofer (History)

    [Duh! Check memory banks before posting!]

    Gun-type assemblies are the easiest to make. That was clear from the beginning. The Manhattan Project planned on a gun-type assembly for plutonium until the summer of 1944, when the first samples were received at Los Alamos from Hanford, and cross sections were measured.

    Great consternation ensued. Seth Neddermeyer’s ideas about implosion, hitherto regarded as a curiosity, became the centerpiece of work on the plutonium device as large chunks of the project were redirected.

    So it wouldn’t be surprising to see a design for a plutonium gun weapon. Germany never got as far as producing plutonium.

  4. commentator (History)

    The drawing in figure 2 was clearly composed after the war. Most of the labels on it are for structural supports, and it is a simple gun-type design. It contains no information which was not released in the Smyth Report. It is not a technical drawing, it is not even likely feasible even in concept.

    If it were implosion, the “explosive” would be what is labeled as “Deckmantel.” My German dictionary says this means “cover”—my bet is that it is what the Germans were translating “tamper” as. Again, nothing that is not in the Smyth Report.

    The need for plutonium implosion only became necessary to the U.S. when it was developing plutonium in reactors—the impurities were apparently not present in cyclotron samples. So if any party knew about the need for plutonium implosion before 1951 (when it was declassified in the U.S. as front-page news during the Rosenberg trial), it meant that 1. they had access to reactor grade plutonium and were calculating its properties, or 2. they had access to U.S. data (viz, the USSR).

    As such, this diagram reveals nothing, except that somebody in Germany speculated about gun-type weapons after the war, most likely after the release of the Smyth Report.

    So why include it? It is a flashy graphic, and most people will slip from “image equals plans equals development” (all quite false slips). Without more information, I would not be inclined to think it had any historical value. Private citizens in the United States drew their own fanciful bomb designs from the 1940s until the present, but it hardly means that they have been running weapons programs.