Question: Charles Louis Critchfield earned his PhD in Physics from George Washington University under the direction of which theoretical physicist who was known as "the father of the hydrogen bomb."

<P0-S0> The W21 was an hydrogen bomb design for the US military. <P0-S1>  It would have used the physics package of the TX-21 bomb. <P0-S2>  The TX-21 was a weaponized version of the "Shrimp" device tested in the Bravo shot of Operation Castle. <P0-S3>  A TX-21C was tested as the Navajo shot, Operation Redwing. <P0-S4>  The TX-21, was a scaled-down version of the Runt device (M-17 hydrogen bomb). <P0-S5>  Smaller in size and weight to the Mk-17, the Mk-21 was considered as a potential missile warhead. <P0-S6>  Far more powerful than the TX-13, which was a high-yield atomic bomb developed from the Mk-6 bomb, the XW21 was to replace the XW13 in the weapons pod of the B-58 bomber and for the SM-64 Navaho missile. <SEP> <P1-S0> Jordan Carson Mark (July 6, 1913 – March 2, 1997) was a Canadian-born mathematician best known for his work on developing nuclear weapons for the United States at the Los Alamos National Laboratory. <P1-S1>  Mark joined the Manhattan Project in 1945, and continued to work at Los Alamos under the leadership of Norris Bradbury after World War II ended. <P1-S2>  He became the leader of the Theoretical Division at the laboratory in 1947, a position he held until 1973. <P1-S3>  He oversaw the development of new weapons, including the hydrogen bomb in the 1950s. <P1-S4>  On the hydrogen bomb project he was able to bring together experts like Edward Teller, Stanislaw Ulam and Marshall Holloway despite their personal differences. <SEP> <P2-S0>  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. <P2-S1> Charles Louis Critchfield (June 7, 1910 – February 12, 1994) was an American mathematical physicist. <SEP> <P3-S0> Edward Teller (Hungarian: "Teller Ede" ; January 15, 1908 – September 9, 2003) was a Hungarian-American theoretical physicist who was born in Hungary, and is known colloquially as "the father of the hydrogen bomb", although he claimed he did not care for the title. <P3-S1>  He made numerous contributions to nuclear and molecular physics, spectroscopy (in particular the Jahn–Teller and Renner–Teller effects), and surface physics. <P3-S2>  His extension of Enrico Fermi's theory of beta decay, in the form of Gamow–Teller transitions, provided an important stepping stone in its application, while the Jahn–Teller effect and the Brunauer–Emmett–Teller (BET) theory have retained their original formulation and are still mainstays in physics and chemistry. <P3-S3>  Teller also made contributions to Thomas–Fermi theory, the precursor of density functional theory, a standard modern tool in the quantum mechanical treatment of complex molecules. <P3-S4>  In 1953, along with Nicholas Metropolis, Arianna Rosenbluth, Marshall Rosenbluth, and Augusta Teller, Teller co-authored a paper which is a standard starting point for the applications of the Monte Carlo method to statistical mechanics.