Talk:Manhattan Project

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Project launch date

The article contains much verbiage but one simple fact has not been included or made clear. On what date was this project launched? ~2025-43423-41 (talk) 10:07, 19 March 2026 (UTC)

The article says: "On 9 October 1941, President Roosevelt approved the atomic program after he convened a meeting with Vannevar Bush and Vice President Henry A. Wallace." Hawkeye7 (discuss) 18:55, 19 March 2026 (UTC)

I would put 17 June 1942 as the actual beginning of the Manhattan Project — the production phase of things. October 1941 is when it moves from the research program (Uranium Committee) to a pilot program (S-1 Committee). June 1942 is when it goes from a pilot program to a production program (Manhattan Engineer District/DSM Project). The latter is what I would consider the Manhattan Project proper, even though the name didn't come into use until mid-1943 or so. NuclearSecrets (talk) 17:25, 26 March 2026 (UTC)

(This inspired me to do some editing of the Origins section to make these kinds of things clearer.) NuclearSecrets (talk) 18:17, 26 March 2026 (UTC)

Semi-protected edit request on 10 June 2026

Change "(equivalent to about $28 billion in 2024)." to "(equivalent to over $30 billion in 2026)." Unlucky Character 12 (talk) 21:54, 10 June 2026 (UTC)

 Not done Inflation is calculated from the latest published GDP figures using the {{inflation}} template. You would need to supply 2026 inflation, which we do not yet have. Hawkeye7 (discuss) 22:19, 10 June 2026 (UTC)

force or heat starts fusion?

@NuclearSecrets and NPguy: Does force or heat start a nuclear fusion reaction in deuterium and tritium?

I don't have easy access to Rhodes (1986), but famous experiments on the Mechanical equivalent of heat established that force acting through a distance, e.g., compressing deuterium and tritium (and ordinary hydrogen?) into a small enough space starts that chain reaction with increasing heat generates further compression. The nucleus is a tiny fraction of the volume of an atom, so compressing two atoms into the volume of one would seem to be necessary but not sufficient for the described fusion reaction.

I'm reverting the latest change by User:NuclearSecrets. ??? DavidMCEddy (talk) DavidMCEddy (talk) 10:00, 31 August 2026 (UTC)

I have access to Rhodes. The deuterium and tritium nuclei have to become sufficiently energetic to overcome the nucleic electrical repulsion. Hawkeye7 (discuss) 10:46, 31 August 2026 (UTC)

It would be more precise to say that the energy from a fission explosion ignites a fusion reaction. Ignition involves a combination of heating and compression, but that wasn't understood until later.

I am puzzled by the deletion of a couple of references to Bethe, e.g.

Teller proposed scheme after scheme, but Bethe refused each one. The fusion idea was put aside to concentrate on producing fission bombs. (this could be reworded to say that Bethe rejected repeated proposals by Teller to work on various fusion schemes to focus on producing fission weapons)

The worry was not entirely extinguished in some people's minds until the Trinity test. (part of the deleted footnote) NPguy (talk) 15:32, 31 August 2026 (UTC)

Thanks to User:Hawkeye7 for checking Rhodes and to User:NPguy for additional comments. DavidMCEddy (talk) 15:40, 31 August 2026 (UTC)

In the initial ideas the paragraph is talking about (very early Super work, what became known as the Runaway or Classical Super) it was entirely heat that was meant to start the fusion reaction. They did not consider compression at that time. ("Why not?" is an interesting and technically complex question, but too distracting for this article.)

In reality, that turned out to be an insufficient understanding of it, and that approach wouldn't work. But it was not until after the Manhattan Project that they figured that out. The actual Teller-Ulam design breakthrough involved a number of other innovations, notably pre-compressing the fuel before heating it

For this article, I don't think any details about that are necessary or relevant except perhaps to note that it wasn't easy to see whether it was right or wrong and it wasn't until some years later that they actually understood how to do it.

I removed the Bethe reference because it isn't quite right. Bethe disputed aspects of the early ideas, but he didn't "refute" them. By the end of the discussio everyone thought that the Super was plausible, but it wasn't clear whether it really would work or not. It makes it sound like Bethe disproved the thing. He did not. The problem with the Classical Super is that it could not be easily proved or disproved with the knowledge and capabilities they had at the time, and it did not happen until 1950.

Bethe did argue against the problem of atmospheric ignition. I wonder if that is getting confused in here (they are, in fact, historically related topics, but not quite the same problem!). I think Ellsberg (my cite) makes a good case for the fact that Bethe's 1970s recollections of this overstate the confidence levels quite a bit, making it sound like it was entirely a non-issue (which it may have been for Bethe, but not everyone was Bethe), when they actually took it a bit more seriously than that.

Teller did not really make any proposals to build the Super during the war. He was just more interested in it than fission weapons, which he thought were boring from a physics perspective. Oppenheimer agreed that Teller could continue to devote time to the Super, not because he thought it would be possible during the war, but because it was an important part of thinking about the future of nuclear weapons. It played a role, closer to the end of the war, in discussions about why international control was important — the possibility of the Super was meant to push away any notions that the weapons of WWII were the "final" form of this technology. --NuclearSecrets (talk) 15:26, 5 September 2026 (UTC)

Who are James C. Marshall and Kenneth Nichols?

@NuclearSecrets:, @Frodnirdon: If Leslie Groves and J. Robert Oppenheimer are NOT listed in the infobox, then I think the "commander" item should be removed.

I see FAQs explaining why James C. Marshall and Kenneth Nichols are listed as "commanders" and Groves and Oppenheimer are not "commanders". I am not an expert on the Manhattan project, but I've seen many discussions of it that featured Oppenheimer and other leading scientists and Groves. I do not recall having heard of JC Marshall nor Nichols before.

The Manhattan project was NOT an ordinary military operation, for which "Commander" would be important. Were JC Marshall nor Nichols important? Doubtless, but not nearly as important as Oppenheimer and Groves, in my judgment.

??? Thanks, DavidMCEddy (talk) 11:32, 23 September 2026 (UTC)

From the linked articles, it appears that James Marshall was briefly in charge at the beginning, before Groves. Nichols was Groves's deputy and was never in charge. I edited accordingly. NPguy (talk) 15:06, 23 September 2026 (UTC)

The infobox is of type Infobox military unit is for the specific military entity of the Manhattan District. I agree that it is confusing, but you can't just put other names in there willy-nilly. Marshall and Nichols were the District Engineers, the official commanders of the District. Groves was a different level above them, as the head of the Manhattan Project. Oppenheimer was not an official commander of anything, militarily; he was the director of Project Y and considered the Scientific Director of the project. See the org chart on the page. Another org chart (in Jones, Manhattan: The Army and the Bomb) includes the President and Secretary of War as part of the Manhattan Project, as just an example of how expansive that definition can be. Jones describes the Project as "the term that by mid- 1943 most accurately described the Army's overall administrative organization for the atomic bomb program," as opposed to the District which was the part of the Army Corps of Engineers that was involved. Jones further points out that once Groves took over, "the Corps of Engineers continued to assist the project, the latter functioned as a basically independent organization, with the Manhattan commander [Groves] having responsibility to the Army Chief of Staff and Secretary of War and through them to the President."

Personally, I think the infobox ought to be less concerned with the formal body of the Manhattan District, as that is (as the article explains) only part of what was the Manhattan Project, and is indeed confusing to explain, and is not clear to the average person reading the infobox alone (they need to know the difference between Manhattan Project, which is the title of the article and how most people know about it, and the Manhattan District, which is not the title and a more obscure aspect of it).

The difficulty, I gather, is that "Manhattan Project" is a much more nebulous administrative entity, whereas Manhattan District is well-defined in terms of leadership, start date, etc. I do wonder if there is a way to indicate Groves was the overall Commanding General for the Project. I do not think Oppenheimer needs to be in the infobox (because if you include him, you open up the floodgates for other people of similar standing — directors of other sites, for example). I also don't know what infobox options there are for nebulous things like this, but I am sure there must be one that fits better than the one so narrowly focused on the District.

Just my two cents... but anyway, that's why you can't list Groves and Oppenheimer as the commanding officers of the Manhattan District. And why Nichols, in fact, was the commanding officer of the District. NuclearSecrets (talk) 15:37, 23 September 2026 (UTC)

There was a discussion and the consensus was to keep the infobox for the district, and not to have separate articles on the district and the project. It is unusual to have an infobox for a unit that is not the title of the article but it is not unique and we even have some articles with more than one unit infobox. Hawkeye7 (discuss) 19:43, 23 September 2026 (UTC)

Shouldn't we use a different infobox, one that names Oppenheimer and maybe also Groves as leaders?

I don't see that there would be any reasonable dispute about Oppenheimer being the lead. The section on "J. Robert Oppenheimer#Postwar activities" begins by saying, 'Once the public learned of the Manhattan Project after the bombings of Hiroshima and Nagasaki, Oppenheimer—suddenly a household name as the "father of the atomic bomb" ... .'

During the "Second Red Scare" of McCarthyism (1947-1959), Oppenheimer was attacked, partly because of his reluctance to build the much-more powerful Thermonuclear weapons. The section of the Wikipedia article on Oppenheimer on "Atomic Energy Commission says that he "and others were concerned about the opportunity costs that would be incurred if nuclear reactors were diverted from materials needed for atom bomb production to the materials such as tritium needed for a thermonuclear weapon." The section on "Security hearing says that, "most in the scientific community saw him as a martyr to McCarthyism, an eclectic liberal unjustly attacked by warmongering enemies".

If you want to say, "There was a discussion", can you please provide a link to the archives of said discussion?

Talk:Manhattan Project/Archive 1#Notable commanders Hawkeye7 (discuss) 19:54, 24 September 2026 (UTC)

If you want to retain the "Manhattan District" infobox, can we move it to the section on "Manhattan District"

Thanks, DavidMCEddy (talk) 13:29, 24 September 2026 (UTC)

To my mind, listing Nichols and Marshalls as "commanders" of the "district" is worse than useless. It is misleading. If kept, the infobox should inform, not confuse. Groves was in charge. I'm inclined to delete the infobox and incorporate it into the text of the corresponding section. NPguy (talk) 19:17, 24 September 2026 (UTC)

I agree with User:NPguy, although I would think there should be an infobox for a project -- or a reasonable interpretation of infobox rules -- that would support naming both Oppenheimer and Groves as key leaders: Oppenheimer as the technical lead and Groves managing the budget. DavidMCEddy (talk) 19:40, 24 September 2026 (UTC)

Groves was the director of the Manhattan Project. He was in charge of all aspects. He made all the decisioons. Oppenheimer was director of the Los Alamos Laboratory. He was not the technical lead!!! Oppenheimer ranked lower than the other project directors, Ernest Lawrence, Arthur Compton, Harold Urey. There is no way that Oppenheimer rates a mention in the infobox. Hawkeye7 (discuss) 19:43, 24 September 2026 (UTC)

I'm confused: The Wikipedia article on Ernest Lawrence says, "When a uranium bomb was used without warning in the atomic bombing of Hiroshima, Lawrence felt great pride in his accomplishment." That's nowhere near the acclaim that Oppenheimer received, at least if we judge by the Wikipedia articles on the two.

I could not find "Hiroshima" mentioned at all in the articles on Arthur Compton and Harold Urey. The article on Compton merely says he "was a key figure in the Manhattan Project". The article on Urey says, "in 1939, Urey was recognized as a world expert on isotope separation", which was needed to separate uranium 235, which is fissile, from uranium 238, which cannot be used by itself on a bomb.

Secondarily, could you please provide a reference to the "discussion and the consensus was to keep the infobox for the district", as I previously requested? Thanks, DavidMCEddy (talk) 21:10, 24 September 2026 (UTC)

Already done above. Hawkeye7 (discuss) 22:15, 24 September 2026 (UTC)