The German nuclear weapons program (; informally known as the Uranverein; ) was an unsuccessful scientific effort led by Germany to research and develop atomic weapons during World War II. It went through several phases of work, but in the words of a historian, it was ultimately "frozen at the laboratory level" with the "modest goal" to "build a nuclear reactor which could sustain a nuclear fission chain reaction for a significant amount of time and to achieve the complete separation of at least tiny amount of the uranium isotopes." Scholarly consensus is that it failed to achieve these goals.