Hans Bethe, a German-born physicist who later became a prominent figure in the Manhattan Project, played a crucial role in the US's development of the atomic bomb. While not a "helper" in the sense of working with the Germans, his contributions were vital to the US effort after he fled Nazi Germany. Bethe's work included understanding nuclear fusion and developing formulas for explosive yield and critical mass......there is no way, you're gonna convince me that American's did this all on their own, google is awesome.
