Talk:Little Boy

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Critical mass and amount of uranium

The assembled fissile core had more than two critical masses of uranium-235

Where does this come from? Critical mass of U235 is 52kg, and the article says the bomb contained 64kg of uranium. Thus, it can not be "more than 2 critical masses", and the statement saying one of the parts had to have "over one critical mass" is wrong too. — Preceding unsigned comment added by 181.74.144.146 (talk) 07:18, 31 January 2024 (UTC)

"Number built"

The info box says, without citation, that 33 LB units were built. What is the source for this number? Carey Sublette says 5. John Coster-Mullen seems to say 13 partial assemblies ("Since units L1, L2, L5, and L6 were dropped in tests at Tinian and L-l1 was used at Hiroshima, this would seem to indicate that there were at least eight (partial or complete) Little Boy weapons available in the inventory at the end of the war. Combined with the five produced at Sandia between 1945 and 1950, it would appear that a total of 13 LB units may have been in existence at that time, although some of these might also have been scrapped."), but that might just be a different way to talk about Carey's 5. RDD-8 says (page 107) there were no more than 2 LB non-nuclear assemblies by 1948 and 0 nuclear assemblies. Anyway 33 seems pretty large to me, and somewhat unlikely! NuclearSecrets (talk) 04:57, 6 September 2023 (UTC)

The article says:

The Navy Bureau of Ordnance built 25 Little Boy assemblies in 1947 for use by the nuclear-capable Lockheed P2V Neptune aircraft carrier aircraft (which could be launched from, but not land, on the Midway-class aircraft carriers). Components were produced by the Naval Ordnance Plants in Pocatello, Idaho, and Louisville, Kentucky. Enough fissionable material was available by 1948 to build ten projectiles and targets, although there were only enough initiators for six. All the Little Boy units were withdrawn from service by the end of January 1951.

Hawkeye7 (discuss) 05:25, 6 September 2023 (UTC)

If you look at the Hansen (Swords, v.2, V-115 and V-117), you'll see that there is some trickiness in terminology here. BOA produced 25 "revised" MK I "mechanical assemblies" (?), but by the end of 1948 there were "no stockpiled fissionable components" and "only two outer casings." He then confusingly blends the "enough fissionable material" for ten (but only 6 initiators) by the end of 1947 (in version 2 of Swords), but then confuses things a bit by saying that there were no gun-type targets and projectiles in the stockpile until 1949 (which implies there may have been a few between 1949 and their retirement by fall 1950). Earlier he says "Only five complete LITTLE BOY weapon assemblies were built between August 1945 and February 1950; all were retired by November 1, 1950." (V-115) It is all very typical Hansen; a lot of miscellaneous quotes that don't quite add up to a coherent whole. He was a fantastic acquirer of documents, but his abilities as a writer and at historical synthesis...

None of this quite gets to 33 by my count, but in any event, 33 seems like the most exaggerated and overly-generous read of the word "built" (it seems to be including partial non-nuclear assemblies, which I think nobody would count a steel gun-tube by itself, or even just a casing, as an actual "atomic bomb" that has been "built"). I would find "5" to be a much more sensible figure to put with "number produced" for an info box, and it would jibe with the other sources (including Hansen), with more details in the article itself. The source of the "5" is apparently Furman, Sandia National Laboratories: The Postwar Decade, University of New Mexico Press, 1990, which I do not have immediate access to, but have made a request through my Interlibrary Loan as I am curious about it in general... -

Anyway I propose (and have made the change) to say that the "number built" for the infobox is 1 wartime + 5 postwar. That seems like a reasonable read of the above, and is more clear than just saying "6" (which is the other alternative way to do the count, I think -- it is interesting that the wartime one is rarely counted!). -NuclearSecrets (talk) 12:07, 6 September 2023 (UTC)

There were eight Little Boy wartime assemblies deployed to Tinian: L-1, L-2, L-3, L-4, L-5, L-6, L-7, and L-11. Hence the total of 33 = 8 + 25. What if we change the number to 13 = 8 + 5? Hawkeye7 (discuss) 19:35, 6 September 2023 (UTC)

I think it comes down to what definition of "built" or "produced" is used. I don't consider any but L-11 to be truly a "built Little Boy." Any more than I consider John Coster-Mullen's reproduced casing to be a "built Little Boy." I think if you told people that "8 Little Boy bombs were produced during World War II" they would be very surprised — because they would (I think correctly) assume you meant that those were complete bombs, and not just partial assemblies of non-nuclear components in all but one case. In my mind, having 8 non-nuclear assemblies + 1 nuclear core means you only have produced one atomic bomb, not eight. I think the goal here needs to be clear. 1 wartime + 5 postwar implies that the US never had more than 6 actual Little Boy bombs that could be detonated, which sounds right to me. Further details in the text can (and should) explain that other non-nuclear assemblies were created in whole or in part, but I don't think most people would consider those anything but incomplete without the (all important) nuclear fuel that converts these from "things that would kill you only if they happened to hit you in the head and break your neck" to "atomic bombs." --NuclearSecrets (talk) 21:12, 8 September 2023 (UTC)

Furman: "Only five complete Little Boy weapon assemblies were built". So we are talking about assemblies here, not "complete" bombs. My understanding is that all the wartime assemblies were used or scrapped. This is the same as with Fat Man; what they had was components to build bombs, but they had to be assembled. The Fat Man cores were stored separately. We don't know how many Little Boy cores were produced post-war; there was only the one during the war. If there was any, they would have been stored separately too. Hawkeye7 (discuss) 22:17, 8 September 2023 (UTC)

I know they had their cores kept separately, of course. "Weapon assemblies" can mean a lot of different things in different Sandia docs, from what I can tell.

I went down a deep rabbit hole to see if I could find any info on postwar core manufacturing. I did find some evidence that they clearly cast some LB core pieces in the postwar, e.g. this document from January 1947 which describes them casting, machining, and electroplating a number of target rings, projectile rings, bolts, and LB initiators at Los Alamos. (JCM says in one place that LB had rings each in the target and projectile, and in another place he says there were six target discs, and it is separately interesting that the DOE says that no complete nuclear components for LB were available in the stockpile in 1947, and I can't explain those contradictions, but I thought this all was interesting.) Los Alamos was clearly in charge of doing all of the U-235 machining at that point, and had a pretty substantial inventory of HEU on hand by 1948 (see page 6, at bottom).

My sense in going over Sandia records is that they did make some number of postwar nuclear components as part of the "Road" program for MK I and MK III bombs (which was a kind of postwar standardization program of the part kits for these early bombs in the late 1940s). For example, this document from February 1949 describes a component catalog (on page 11) for the "nuclear material" of the LB bombs, and item 2.3.3 (on page 12) describes parts "LB-12, LB-13, and LB-14," which I suspect correspond to the projectile, target, and initiator pieces. However it also may indicate that at that time, they hadn't actually made those pieces as such (there is a tentativeness to the description, "in the event that the need... occurs"). The same document also makes reference to the idea that there were at least three different models of postwar LB (Type AAA, B, and C, on page 13). The grammar is a little hard to parse; it may be that B and C were the "mockup" and "ballistic assembly," or they may be different things entirely. There is an interesting discussion of "inventory" on page 14, which makes it clear that in 1949, they had lots of parts available or close to being available, but it sounds like nothing had really been put together. This document says that during FY 1949, they finished the "Road catalogues" of components and turned the components over to the AFSWP, but that can't include nuclear components, since those were not given to the military at this stage of things. It also says manufacturing of "major components" was completed in November 1948, but doesn't specify what those are, of course. This May 1948 progress report says that "two gadgets" of the LB type had been prepared for "possible military emergencies", and those must be the cited 2 non-nuclear LB's ready in 1948 (it's nice to be able to at least find something that verifies that number!).

The whole history of the Navy's involvement with the Manhattan District and then Sandia on this is pretty interesting (a USAF historian in the late 1950s considered it "somewhat devious," and apparently the USAF strongly, strongly opposed this program, because they felt that this was a misuse of scarce fissile material), and it seems to overlap with the history of the Mk 8 in interesting ways. The inter-service rivalry aspect is pretty fascinating to me. I am very interested in the early Truman admin nuclear stockpile at the moment, which is why I am diving into this (beyond the inherent interest of scratching around at an issue that is not super well-documented).

ANYWAY. All of this is very sketchy, obviously, and not likely usable in the article (too WP:OR), but I thought it was interesting and worth just writing down. My sense is that we might just want to not condense all of this into a "number produced" at all, because it's just not a meaningful number at present, and instead just indicate the various numbers and their possible meaning in the text. I consider it very likely that the number of five produced in the postwar means that they considered these "full" (including nuclear) assemblies that could have been put together on short notice (e.g., without casting projectile or target pieces), because otherwise that distinction of "five" makes no sense and it seems to be one that Russ makes (versus the 20ish mechanical assemblies number). I sort of feel like if the Furman book says five (and everyone else says "five") then that's the sensible postwar number, assuming it doesn't include LB-11 in it. --NuclearSecrets (talk) 21:00, 10 September 2023 (UTC)

Sounds good to me. Thanks for going down the rabbit hole. Much appreciated. (I've always enjoyed scratching around at an issue that is not super well-documented myself.) LB-12, LB-13, and LB-14 sound like assemblies to me, continuing the series from the wartime one that ended with LB-11. I first came across the Navy's post-war nuclear ambitions plans in I wrote the article on the Armed Forces Special Weapons Project mainly because having read about the Manhattan Project, the question of "what happened next?" came up, and I thought that other people would be interested too. (Page counts say otherwise though.) Hawkeye7 (discuss) 21:30, 10 September 2023 (UTC)

References

More on postwar

So we have this:

Enough fissionable material was available by 1948 to build ten projectiles and targets, although there were only enough initiators for six. However, no actual fissionable components were produced by the end of 1948, and only two outer casings were available.

Which cites Hansen 1995 (vol 5), 116-118. Hansen's text says:

By the end of 1948, there were no stockpiled fissionable components for the LITTLE BOY and only two outer casings.[123]

There were no gun-type weapon uranium targets and projectiles in the national nuclear weapons stockpile again until 1949, although by the end of 1947, enough fissionable material had been assembled to build 10 projectiles and targets. There were only enough initiators on hand for six of these potential weapons.[124]

Footnote 124 is a document that I have, which is a report for the state of things as of December 31, 1947. It has a table relating to both FM and LB weapons, which has two columns, "Accepted" and "Under test." For LB, it has a row for "Fissionable material" and indicates 10 are "under test." It also says it has 6 initiators under test. And under "Other components (in terms of complete assemblies)" it has 0.

Footnote 123 cites an unpublished talk which seems not to be digitized anywhere (so impossible to check or use), as well as the familiar DOE stockpile report, which says 2 full non-nuclear assemblies and 0 "nuclear components."

Anyway, just documenting this. My reading of the 1947 document suggests they in fact did have 10 projectile/targets cast — I don't think "under test" means they hadn't tested them, I think it means they were in quality assurance or something like that. The document does not elaborate at all — it is just a one page table, nothing more.

I admit I am a little suspicious of the DOE stockpile numbers. The DOE numbers say that the US had 29 implosion non-nuclear components, and 13 nuclear components in 1947. But the report in question says that the AEC had _50_ implosion cores (9 "pure 49 Christy", 36 "composite Christy", and 5 "levitated composite") in the "accepted category" (with 11 "under test"), 63 initiators, 44 assembled HE components (28 unassembled), 104 "other components". I don't know how to reconcile those differences except to suggest that the DOE numbers are perhaps meaning something different than we might assume they mean. Or that there's some other confusion there — the DOE list says "Fiscal Year" where as the report is about components on hand in December 1947, which is not quite the same thing. So maybe they are rolling the December 1947 data into FY 1948 (which does list 50 implosion cores). In which case, the "0" for 1948 really means for FY 1948 and not "by the end of 1948." NuclearSecrets (talk) 21:45, 8 March 2024 (UTC)

Hansen cites are a little mixed up

So all of the Hansen cites claim to be for the 1995 edition of Swords. But from what I can tell they are actually the 2007 edition (version 2). At some point I will make them all the same version, because the page and volume numbers are not the same between them at all. Just a note. NuclearSecrets (talk) 17:16, 10 March 2024 (UTC)