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 an all-out program to develop the so-called Super Bomb. Two and a half years later, thanks to the determined efforts of Edward Teller and colleagues at the Los Alamos Scientific Laboratory, the U.S. detonated the first thermonuclear device, beating the Soviets to the H-bomb by more than three years.
Fuchs' betrayal of the H-bomb secrets passed into the folklore of the nuclear age. The folklore, however, is false. Fuchs' H-bomb plans were totally misleading, and Truman's rationale for rushing to build the bomb before the Soviets did was on shaky ground. That is the conclusion of an article in the January-February issue of the Bulletin of the Atomic Scientists, one of a series of scholarly works that are rewriting a period of U.S. history still shrouded in mystery and official secrecy. According to Daniel Hirsch and William Mathews, what Fuchs gave the Soviets was an early design of Teller's that turned out to be unworkable. The crucial insight, they say, came after Fuchs had been imprisoned, and it was supplied not by Teller but by his Los Alamos colleague Stanislaw Ulam. Says Hirsch, former director of the nuclear- policy program at the University of California at Santa Cruz: "In many ways, Stan Ulam was the true father of the H-bomb."
The key to the new account is a top-secret history of the H-bomb written by Hans Bethe in 1952 and only recently declassified. According to Bethe, who headed the theoretical-physics division at Los Alamos during World War II, Teller's design began to fall apart shortly after Truman launched his H-bomb program. Teller's idea had been to use the heat of a conventional A-bomb to ignite a separate H-bomb. But Ulam, a brilliant mathematician, made a series of calculations that showed that the amount of tritium fuel required for Teller's bomb was prohibitive and that even when sparked by an A-bomb, it would probably not achieve fusion.
The breakthrough idea was the recognition that the fuel would burn more efficiently if it was compressed before it was heated. According to Bethe, Ulam approached Teller with a two-stage H-bomb design that used the shock waves from an A-bomb to compact the hydrogen and ignite the H-bomb. Teller adapted Ulam's design, using the energy of the A-bomb's radiation rather than the force of its shock waves to achieve the necessary compression. It was a bomb of this design, code named Mike, that exploded on Nov. 1, 1952, on the Pacific island of Elugelab. The island, one mile in diameter, disappeared.