Not really relevant to the original query
But I read somewhere, many years ago, that the Allied high command had recognised, quite early on, that the heavy water route to an atomic wespon wasn't really viable back then.
The Germans were also trying a different fission programme which would have yielded results.
Therefore, in a classic piece of bluff, one minor half-cocked raid was carried out on the alternative plant, but a good few raids were carried out on the Norwegian heavy water production.
This caused Germany to concentrate it's research on the 'heavy water red herring' and thus fail in it's race for the bomb.
I'm not sure of the truth behind this - it was so long ago I read it that it could have been fiction!
From memory (of reading a book, I'm not that old)....
There was a meeting between Heisenberg - who was, essentially, in charge of the German research program into nuclear energy/science and Neils Bohr, both big scientists of course, in about ~1941 I think, and the British managed to get word back from Bohr that they
interpreted that he said that the Germans were well on their way toward building a nuclear weapon. (At this time the British had worked out that such a weapon was feasible...but lacked the resources to really make a start on it.)
In reality they were purely paranoid and had completely misinterpreted Bohr (I think he was asking if someone he knew, a nanny I believe, was okay!)
Anyway, both sides were trying to build a nuclear reactor, as this was the first step in producing fissile material, generate heat etc, and this new material produced the Allies
knew could be used in a bomb. However, I don't think the Germans had quite figured out the fissile material bit and then bomb - I think they needed to get supplies of plutonium first to test its properties and then they would have probably made the breakthrough.
However both sides, at the time, knew there were two ways they could tackle the problem of making radioactive criticality - the first step - one using graphite in a stack or pile as a control mechanism, the other using heavy water. The US, with the help of Enrico Fermi and many others successfully built a stack, whereas the Germans definitely went with the heavy water option - which was fortunate as Heisenberg never made his water reactor go critical, I think. Both decisions of either party were taken well before any spies could make them change their minds.
Anyway, the allies didn't know this and probably presumed, from their Norwegian operatives that the Germans were ordering loads of heavy water, and that perhaps the Germans had indeed built a working heavy water reactor (As they did not try to build a heavy water reactor, they did not know if it was more difficult to do). Hence their various schemes to limit German access to the stuff, just incase.
BTW it's not clear that the Germans in their program really got anywhere close to realising that they could have made a nasty weapon. They
thought they were well ahead of the allies, but when the British got Heisenberg and quite a lot of the other German nuclear scientists together in captivity and revealed to them Hirosoma and Nagasaki, apparently in private (y'know spying on them with microphones and stuff), the German scientists were shocked at how far behind they actually were.
So not really a bluff, but more that the allies were paranoid that the Germans were years ahead of them., Thankfully they were no where close!