What if no Soviet spy in Manhattan project?

What if there was no Soviet spy in the Manhattan project? In OTL Klaus Fuchs was the spy that provided Soviets information about the nuclear bomb, but how long would the Soviet nuclear program have been delayed if Fuchs had got caught early on, or if he had not ended up in the project to begin with?

Also, how would it have affected the early cold war?
 
I remember how in Oppenheimer, Leslie Groves said years later at Oppenheimer’s Security Clearance hearing that he wouldn’t hire Oppenheimer under their current anti-Communist regulations, but neither would he hire more than half of the scientists that were on the project due to almost all of them having some sort of Marxian-Sympathies.
So, even if there was no Klaus Fuches to spy on the Manhattan Project for the USSR, there would still be at least some scientists willing to do so later on.
 
Even if the Soviets somehow didn't get wind of the Manhattan Project at all, the fact that two bombs were dropped on Japan will give them the kick in the pants to want a programme of their own.

The science was already known about - it's literally just a matter of time before a Soviet bomb happens.
 
Even if the Soviets somehow didn't get wind of the Manhattan Project at all, the fact that two bombs were dropped on Japan will give them the kick in the pants to want a programme of their own.

The science was already known about - it's literally just a matter of time before a Soviet bomb happens.

The Manhattan project had more than just Fuchs, there were several Soviet agents - the Rosenbergs recruited at least two (including Ethel's brother)

You also have Melita Norwood, who worked on the British TUBE ALLOYS project, which was folded in to the Manhattan Project

You need to get rid of a number of Soviet agents
 
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Sure, but the question is that for how long it would delay them?
Britain had started the tube alloys project, initially alone, joined the manhattan project, but lost the access to nuclear secrets from US, tested it first nuke in early 1950s.
France was ravaged from war, started from scratch in 1945 without any foreign help, with only their native scientists and knowledge, and in early 1960 had their first test.
The USSR, with more resources could had developed a nuke by early 1950s, if Stalin decided to not "cheat".
 
Probably I would guess two to three years. The Soviets weren't really thinking about Gaseous diffusion, so would stick with Electromagnetic separation, and centrifuges, the latter of which are better but will take a long time to work. Functionally most of what the US data did apart from that was allow the Soviets to avoid as much trial and error as the US went through, they still have the talent to do it. So I would say two years, simply because Calutrons, even the improved Soviet design, are less efficient than Gaseous Diffusion, and thus would take more time to make the enriched material in quantity, three years would be the maximum accounting for them having a lot of bad luck in trial and error



Now what does this mean? No bomb until 1951 probably means that Stalin does not give permission to Kim to start the Korean War until 1952 or 1953, assuming it happens at all. If it does happen then the US military will be in even worse shape for a war outside of SAC, and its only options will be to escalate with nuclear weapons or allow a communist victory, which means either a paranoid humiliated US, use of US nuclear weapons to make North Korea back down, or full on nuclear WW3 if it escalates
 
The Manhattan project had more than just Fuchs, there were several Soviet agents - the Rosenbergs recruited at least two (including Ethel's brother)

You also have Melita Norwood, who worked on the British TUBE ALLOYS project, which was folded in to the Manhattan Project

You need to get rid of a number of Soviet agents

Looks like you are right, but Fuchs was still the most important spy. The others apparently had far less impact.

1) How much effect just removing just Fuchs would have?
2) What if most of the other important spies were also removed? Sure, you couldn't get rid of all spies, but most of them had access to a lot less information, I suppose.
 
Theodore Hall was also the other big technical spy, aside from Fuchs. There were others, like the Rosenbergs and Harry Gold, but I'm not sure how much information they could get themselves. Hall and Fuchs were very high in the Manhattan Project's command chain, and no other spy had similar clearances to those two.

But what Hall and Fuchs gave accelerated the Soviet nuclear program by years. A huge portion of the Manhattan Project's time and resources were actually spent on efforts that ended up being dead-ends, so the Soviets getting the final schematics, thus avoided those dead-ends, saved hundreds of millions of dollars and years of resources. If the Soviets had to spend the same amount of resources as the Western Allies and ended up encountering those same dead-ends (plus, the Soviets have a smaller scientific talent pool than the Allies), I would say 1950 is the earliest they could develop their own nuclear bomb.
 
Now what does this mean? No bomb until 1951 probably means that Stalin does not give permission to Kim to start the Korean War until 1952 or 1953, assuming it happens at all.
The issue with Korean war in that scenario is that even if USSR would reel in North and prevent them from starting anything, the South would be still there and they also wanted to start the action. It is just Kim was one who got in position first. So you will still have Korean war but it will start with South trying to invade North and not the other way around.
 
The issue with Korean war in that scenario is that even if USSR would reel in North and prevent them from starting anything, the South would be still there and they also wanted to start the action. It is just Kim was one who got in position first. So you will still have Korean war but it will start with South trying to invade North and not the other way around.
While Rhee might have wanted a war, I doubt he was going to launch one until he had some tanks, artillery or combat aircraft, which the US was slow rolling deliveries of precisely so that he could not start a war. So I seriously doubt Rhee would start one on his own until that happens, which IMO would take longer that the Soviets getting a bomb and giving Kim permission
 
While Rhee might have wanted a war, I doubt he was going to launch one until he had some tanks, artillery or combat aircraft, which the US was slow rolling deliveries of precisely so that he could not start a war. So I seriously doubt Rhee would start one on his own until that happens, which IMO would take longer that the Soviets getting a bomb and giving Kim permission

Did Soviets having the bomb even matter all that much in 1951? They had very limited numbers of them, and their bomber force was quite limited as well.
 
Did Soviets having the bomb even matter all that much in 1951? They had very limited numbers of them, and their bomber force was quite limited as well.
Stalin gave Kim permission to attack in 1950, Kim had asked in 1949 but was told the time was not right. One of the two major changes, apart from the end of the Chinese Civil War, was the Soviet acquisition of the bomb
 

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An alternative scenario is one or more spies are caught and turned to make the Soviets spend months or years on dead ends.
 
Stalin gave Kim permission to attack in 1950, Kim had asked in 1949 but was told the time was not right. One of the two major changes, apart from the end of the Chinese Civil War, was the Soviet acquisition of the bomb

The Soviets had their first bomb test in 1949 though.
 
An alternative scenario is one or more spies are caught and turned to make the Soviets spend months or years on dead ends.
This. Have Fuchs give them carefully prepared false reports on liquid-thermal diffusion, gun-type plutonium weapons, red mercury, etc. If you can monkeywrench their program long enough, maybe Stalin executes Beria, then Kruschev drops the whole project.
 
The Soviets had their first bomb test in 1949 though.
Yes, months after Kim initially asked. It takes time for policy to change and for one to observe international reactions for things to shake out. The bomb was not the only change that mattered, but I would say Stalin needed all of them to occur to be convinced that the US would not escalate things
 
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