a nuclear program based on heavy water from Rjukan in occupied Norway, which was eventually sabotaged and destroyed. It was fears of German nukes that triggered Einstein's famous letter to Roosevelt, and thus the initiation of the Manhattan Project:
The US feared that Norway would be developing its own nuclear weapons in the first years after the Second World War, and on two occasions the US put pressure on Norway to prevent this. This claim is put forward in an article by Chief of Research at the Norwegian Nobel Institute, Olav Njoelstad. According to Njoelstad, US intelligence kept a very close watch on Norway in the first years of the cold war. The reason was Norway's unique position as the leading exporter of heavy water which was used in the development of nuclear energy, as well as Norway's pioneering role in this development, Aftenposten writes. Norway had already in 1951 its own nuclear research reactor at Halden, in south-eastern Norway.