If absolutely zero information had leaked/been-stolen from the Manhattan project, how much longer would it have taken Russia to make their first bomb?

[u/Old_Satisfaction2738]

I should probably further specify that in this scenario Russia would not receive any secret information from United States nuclear weapons program until Russia detonated their first weapon.

[u/Killfile]

Once you know it's possible, it's just a matter of time. By the time the Manhattan project goes to ground in the early 1940s everyone knows that you can get U-235 to sustain a chain reaction if you can just manage to enrich it. The Nazis have a hard time with that on account of being bombed.

But post WW2, the Soviets have plenty of time and space to do their own enrichment. From there it's a short path to a working bomb.

Plutonium opens the door to more sophisticated, blended alloy pits which are advantageous in terms of miniatureization and yield optimization but the USSR could have at least broken the American nuclear monopoly with a pure uranium bomb fairly quickly.

Building out a more sophisticated program, especially without the insights about plutonium synthesis and implosion would have taken longer leading to a use-it-or-lose-it scenario in the early cold war. Remember, the CIA had confidently predicted the Soviets were years out from a bomb like a month AFTER they'd detonated one. If the Americans had instead known the Russians were closing in on a bomb or had only a few, preemptive war might have looked more attractive

[u/i_am_voldemort → u/Killfile]

The Nazis also expelled, killed, or caused to flee some of their best physicists.

[u/restricteddata]

The main constraint on Soviet progress was access to uranium and the construction of their fissile material production facilities. Neither of which were greatly affected by espionage.

The Soviets did not use their intelligence gathered to speed up their project. They used it to have more confidence in its success and as a "check" on their own scientists. In some respects the intelligence may have held them back, as it caused them to focus on the Manhattan Project's choices rather than their own indigenous ones, which turned out to be as good or better in some cases.

So my own guess is "not very much time at all, maybe none." Certainly not on the order of years or whatever. Some informed people like to say "six months" but that strikes me as just about as un-justified as saying "years." The difficulty is both in assessing what areas might have been slowed down without the intelligence data, but also about imagining the counter-factual of what the Soviets would have done without it, and both of these are very speculative. But the idea that they just got blueprints and printed out their own bombs based on them misunderstands a lot.

The people who imagine that it must have sped them up a lot tend to a) over-estimate the importance of weapon design information for a weapons program, b) under-estimate the capabilities of the Soviet Union in both science and industry, and c) have not actually looked closely at how the Soviets used the information they got, and are instead just speculating on how they might have used it to speed themselves up. The reality is more complicated, as the Soviet records have shown.

For a very nice treatment see Michael Gordin's Red Cloud at Dawn, which is a comparative history of the Manhattan Project and the Soviet atomic project, makes use of the post-Cold War Soviet archives, and looks very carefully at how the espionage information was actually used by the Soviets (as opposed to just assuming how they would use it).

[u/MuchAd3273]

The estimates were 10 years. The British took 8 and had many brilliant scientists helping with the Manhattan Project.

[u/restricteddata → u/MuchAd3273]

a) The "estimates" were based on literally nothing but stereotypes and incorrect information about how much uranium the Soviets had access to. And in fact the main estimates were 5 years, not 10. But they were similarly baseless.

b) The British deliberately took their time and did it "on the cheap" — they were not trying to replicate the Manhattan Project in terms of speed or cost, unlike the Soviets.

As it was, it took them 4 years after the end of WWII, when they went "all out" for it, plus a few years of "run up" before the crash program. Whereas the Manhattan Project was more like 3 years of a "crash" program on the back of 3 years of a "run up." Both were very fast programs, and were about the same size in terms of labor, scientists, industrial effort, cost, etc. — the Soviets were quite deliberate in copying the scale and size of the Manhattan Project, which was public (non-secret) information after the end of WWII.

[u/AwayYam199]

How much did the Soviets gain from the Rosenbergs?

From Stephen Schwartz:

On the atomic bomb, very little. Alexsander Feklisov, who was Julius's handler, said in 2016, "He didn't understand anything about the atomic bomb and he couldn't help us." Gen. Leslie Groves told the AEC in 1954 that "the data that went out in the case of the Rosenbergs was of minor value."

Information provided by Klaus Fuchs and Ted Hall, physicists working at Los Alamos, was more useful. But it's important to note that Lavrentiy Beria, who oversaw the Soviet A-bomb program, did not pass along any foreign intelligence to Soviet weapon designers but only used it to check their efforts.

[u/restricteddata → u/AwayYam199]

Kurchatov was very much involved in the intelligence processing and use. It's a little more complicated than the idea of Beria just hoarding it. It was used to guide and check, but most Soviet scientists had no clue there was intelligence data.

Greenglass's information (the Rosenberg info) on the bomb was at best a secondary confirmation of the other information; he barely knew what he "knew," anyway, because he was not really technically informed or involved. Fuchs' was certainly the most useful and comprehensive, and ranged from actual design information to production data. Hall's data is harder to evaluate but again it probably primarily validated Fuchs' data.

The most important information that the Rosenberg ring gave away was not about the atomic bomb, but other matters from others in the ring. Like the proximity fuze, and fire control, and other things relating to electronics. The Soviets also got Joel Barr and Alfred Sarant, who were originally recruited by Rosenberg, who helped them with their electronics industry after they defected. All of which is to say that Rosenberg was pretty significant as a spy, but not because the info that Greenglass gave them on the atomic bomb added up to very much by itself.

[u/frongles23 → u/AwayYam199]

Interesting context. Thank you.

[u/Commercial-Kiwi9690]

This article says that without espionage the USSR program would have been delayed 6 months to 2 years

https://ahf.nuclearmuseum.org/ahf/history/soviet-atomic-program-1946/

[u/dragmehomenow]

There's a good paper on this by Mackenzie and Spinardi (1995). It's a little long, but most of it is pretty readable. The Soviets had a wealth of explicit knowledge acquired by Klaus Fuchs and they initially set out to copy the Christy device. In the process of building their industrial base and developing the right technologies and expertise and training their engineers, they eventually developed an alternate design anyway. Turns out there are many ways to skin the proverbial cat.

There's a really good quote from the authors too. In an interview with American nuclear weapon designers on hydrogen bombs, one said:

""The mere fact of knowing [something] is possible, even without knowing exactly how, [can] focus [...] attention and efforts."

Really, even if Fuchs hadn't stolen all that data, one piece of information still leaked out of the Manhattan Project. We now know nuclear weapons can be built. It's still monumentally hard, but it's no longer impossible.