I would like to learn more about the knowledge each side had of nuclear weapons development. I am aware of allied efforts to destroy German held heavy water treatment facilities in Norway between 1940-44. But, did the Germans know how far along the allies were in nuclear development? And were the Russians, Japanese, and Italians also aware of the development of nuclear weapons? Did the US announce to the British and Russians before attacking Japan with nuclear bombs? Did British, French, and Russian Scientists assist American efforts with the Manhattan project or was this a unilateral effort? Thanks for your input!
In brief:
The Soviets knew about the US bomb work, because they had spies. The UK knew about the US bomb work, because they were part of the project. No other nations had significant intelligence on the US work on the Manhattan Project. The Germans were exceedingly ignorant about US work and were later shocked to learn that they (the Germans) were not the leading authority on such matters in the world.
The US and UK did not know about the extent of German work, but feared they were working on the bomb. So they engaged in attempted sabotage of plants they thought might be helpful to that work. The US had a project (Alsos) that was tasked with determining the extent of German work that went into Italy and France with the Allied invasions there, and determined by late 1944 that the German project was not really a bomb project (it was a small reactor project).
The Japanese were ignorant of the German work, and the Germans were ignorant about the Japanese work. Both had modest projects and both sought to keep them secret from one another. The Japanese, toward the end of the war, convinced the Germans to send them some uranium for their work, but lied about its purpose to the Germans.
I don't think the Italians knew about anybody's work, though they had some vague indications that the Germans were interested in nuclear matters. But not much.
The Manhattan Project did have cooperation with the British, and several British scientists played roles in it. There was also a small delegation of French scientists who were part of the British project, in Canada, but they were kept at arms-length by the Americans, and had very incomplete information on the American work as a result. There were also a number of scientists from different nations who worked on the Manhattan Project (from Germany, Italy, Russia, Hungary, and Poland, among other places), almost all of which had become American citizens by the time of the project