The discovery of nuclear fission by German chemists Otto Hahn and Fritz Strassmann in 1938, followed by its theoretical explanation (and naming) by Lise Meitner and Otto Frisch, opened up the possibility of a controlled nuclear chain reaction with uranium. At Columbia University, Enrico Fermi and Leo Szilard began exploring how this might be done. Szilard drafted a confidential letter to the President of the United States, Franklin D. Roosevelt, explaining the possibility of atomic bombs, and warning of the danger of a German nuclear weapon project. He convinced his old friend and collaborator Albert Einstein to co-sign it, lending his fame to the proposal. This resulted in support by the U.S. government for research into nuclear fission, which became the Manhattan Project.