History: The Master Spy Who Failed

Surprising new facts emerge about the making of the H-bomb

On Jan. 27, 1950, a balding, bespectacled German-born physicist named Klaus Fuchs walked into London's War Office and confessed to being a spy. For seven years, from 1942 to 1949, Fuchs had systematically funneled high-level secrets about U.S. and British nuclear-weapons research to the U.S.S.R., including plans for the yet unfinished hydrogen bomb.

Fuchs' confession and subsequent trial marked a turning point in the history of the cold war. Evidence supplied in the confession led to the arrest of Julius and Ethel Rosenberg for what J. Edgar Hoover termed "the crime of the century" and prompted President Harry Truman to launch...