Before the war, the California Institute of Technology (Caltech) was a leading university in the fields of particle and nuclear physics. It was especially known for its experimental physicists. Many scientists who had important roles on the Manhattan Project were affiliated with Caltech, including J. Robert Oppenheimer, Richard Tolman, and Robert Bacher. In addition, a group working at Caltech under Charles Lauritsen directly assisted in the bomb-building effort, providing help manufacturing detonators that would be used in the atomic bombs.