I'm watching The Heavy Water War on Netflix and while I recognize that the series has some issues with its portrayal of Heisenberg I find myself wondering about the extent to which the British military command knew about the Nazi Bomb project and, specifically, why the Germans were so interested in heavy water to begin with.
The series seems to suggest both that the German bomb project was a well known fact at the lowest strategic level of the Allied military and that the consequences of and significance of nuclear weapons were understood by the same.
This strikes me as suspect but that's a bit out of my wheelhouse.
The US and UK were both very worried about a German bomb project up through 1944. They were specifically suspicious of German interests in the use of heavy water as a reactor moderator, which they knew could be used to generate plutonium in a large reactor.
They knew not too much else — they knew the Germans were interested in heavy water, they knew that there was likely some work being done on fission work, but they didn't know the extent of either. They used worst-case thinking to imagine an extensive, well-funded, well-coordinated German bomb project that they could only see the edges of. In reality the German program was scattered, underfunded, and focused mostly on reactor development (and not bomb production). By 1943 there were indications of this, but it was not until late 1944 that this was confirmed to a degree that they stopped worrying about a German bomb.
I don't know what "lowest strategic level" means in this context; anything related to atomic bombs was heavily compartmentalized so while there were some people at low levels who knew about it, on the whole most people did not.
The US and UK had their own scientists working on atomic matters so they did appreciate the significance of it (the UK got very worried from 1940 onward, the US from 1941 onward).