BRINK OF ARMAGEDDON

With the discovery of fission," C.P. Snow once wrote, "physicists became, almost overnight, the most important military resource a nation-state could call upon." The unleashing of the awesome destructive power of the atom turned physicists into politicians and politicians into physicists. Scientists were forced to reckon with the repercussions of what they had wrought, while political and military leaders had to comprehend the power they held at their fingertips. In Richard Rhodes' epic and fascinating Dark Sun: The Making of the Hydrogen Bomb (Simon & Schuster; 731 pages; $32.50), a sequel to his Pulitzer prizewinning The Making of the Atomic Bomb, Rhodes shows how the failure of scientists and political leaders to understand each others' realms almost brought the world to nuclear Armageddon.

It was said in Washington after the Japanese surrendered that the Soviets couldn't put an atom bomb in a suitcase because they didn't know how to make a suitcase. That was true only to a point: though they had yet to learn how to manufacture decent luggage, Soviet spies had given them a blueprint for the bomb.

To set the stage for his story about the hydrogen bomb, Rhodes deftly recounts the deeds of the perfidious Klaus Fuchs, the German emigre who furnished the Russians with not only a hand-drawn model of the Fat Man bomb dropped on Nagasaki but also the theoretical plans for making the H-bomb. As scientist Hans Bethe remarked later, Fuchs was "the only physicist I know who truly changed history"--but he changed it by passing on nature's secrets, not discovering them.

The one secret the Russians failed to learn was that America's atomic cupboard was virtually bare at war's end. While the Soviets were gearing up their first reactor, the U.S. was shutting its own reactors down. "Everyone dropped their tools and went home when the whistle blew," said a disgruntled General Curtis LeMay, who was soon to head the U.S. Strategic Air Command, the force responsible for delivering the nation's nuclear weapons.

It was the Soviets' test of their first atomic weapon in 1949 that galvanized Washington and U.S. scientists. Something bigger, exponentially more powerful than the atom bomb, had to be built, argued physicist Edward Teller. When Harry Truman was told of Teller's design for a hydrogen bomb, code-named Super, the President said, "What the hell are we waiting for?" The U.S. effort went into overdrive, partly because Washington suspected--rightly, as it turned out--that the Soviets were developing a Super of their own.

To counter this, LeMay actually proposed "a nuclear Sunday punch," a pre-emptive strike against the Soviets. In 1949 he wanted to send an armada of U.S. planes, carrying the entire Los Alamos stockpile--numbering more than 100 atom bombs--to destroy 70 Soviet cities. It was out of fear that a hot-headed general like LeMay might be able to launch a nuclear attack on his own that the Kennedy Administration later instituted a complex chain of commands governing the use of nuclear weapons.