Charles Louis Critchfield (June 7, 1910 – February 12, 1994) was an American mathematical physicist. A graduate of George Washington University, where he earned his PhD in Physics under the direction of Edward Teller in 1939, he conducted research in ballistics at the Institute for Advanced Study in Princeton and the Ballistic Research Laboratory at the Aberdeen Proving Ground, and received three patents for improved sabot designs. In 1943, Teller and Robert Oppenheimer persuaded Critchfield to come to the Manhattan Project's Los Alamos National Laboratory, where he joined the Ordnance Division under Captain William Parsons on the gun-type fission weapons, Little Boy and Thin Man. After it was discovered that the Thin Man design would not work, he was transferred to Robert Bacher's Gadget Division as the leader of the Initiator group, which was responsible for the design and testing of the "Urchin" neutron initiator that provided the burst of neutrons that kick-started the nuclear detonation of the Fat Man weapon. After the war he became a professor at the University of Minnesota, and then vice president for research at the Convair division of General Dynamics, where he worked on the Atlas family of rockets. In 1961, J. Carson Mark and Norris Bradbury offered him a position at Los Alamos, which he held until he retired in 1977. Early life Charles Louis Critchfield was born in Shreve, Ohio, on June 7, 1910, and grew up in Washington, D.C. He received his B.S. (1934) and M.A. (1936) degrees in Mathematics from George Washington University, where he also earned a PhD in Physics (1939) under the direction of Edward Teller. During Critchfield's graduate studies, Teller's colleague George Gamow introduced him to Hans Bethe, with whom he wrote a paper in 1938, which analyzed the nuclear fusion of protons into deuterons. The next year, Bethe showed that this process is a key link in the proton-proton chain reaction and the CNO cycle, which are the major ways that nuclear energy is released in the solar core and in massive stars. In 1967, Bethe was awarded the Nobel Prize for this work on stellar nucleosynthesis. World War II After he graduated, Critchfield taught optics for a year at the University of Rochester at the invitation of Victor Weisskopf. In 1940, he was awarded a National Research Council fellowship, and went to work under Eugene Wigner at the Institute for Advanced Study in Princeton. At