I'm currently reading a biography of Oppenheimer, specifically the time of the Manhattan Project and was wondering where the theory that an atomic bomb was feasible came from? Specifically by whom and also how did the US know it was such an important goal of the Nazis, hence leading to the US putting in such an effort to create one first.
/u/restricteddata's answer to Thirty-four years after scribbling E = mc2, Albert Einstein wrote to President Franklin Roosevelt to warn him the Nazis were turning his famous theory into a nuclear weapon. How did Einstein know this, and did Roosevelt actually read his letter? provides a nice narrative of the conceptual origins of nuclear weapons and the Manhattan Project