So, we dropped an atom bomb. But what is an atom bomb?
The Smyth report of August 1945
“Sixteen hours ago an American airplane dropped one bomb on Hiroshima,” Harry Truman declared on August 6, 1945. “That bomb had more power than 20,000 tons of T.N.T. It had more than two thousand times the blast power of the British ‘Grand Slam,’ which is the largest bomb ever yet used in the history of warfare.” What kind of bomb was this new weapon? “It is an atomic bomb. It is a harnessing of the basic power of the universe. The force from which the sun draws its power has been loosed against those who brought war to the Far East.”
Truman’s announcement marked the first time most Americans had ever heard of an atomic bomb, and the announcement didn’t shed much light on the subject. So six days later – after a second atom bomb had been dropped, on Nagasaki – the president approved the release of a report written by Henry De Wolf Smyth, titled “Atomic Energy for Military Purposes.” Harry Smyth was chairman of the Princeton physics department and a participant in the Manhattan Project, the top-secret program that built the atom bomb. He employed his twin talents as a scientist and an educator to explain to the American people, and the world, what this breakthrough consisted of. Smyth’s report had been written weeks earlier but withheld from public view; now that the existence of the bomb was no longer a secret, Truman allowed the report’s publication.
Smyth acknowledged that the subject of atomic energy was complicated; his report was not for everyone. “This report is intended to be intelligible to scientists and engineers generally and to other college graduates with a good grounding in physics and chemistry,” he said. Yet even for them, the reading went slowly in places.
Most Americans knew of Albert Einstein, the German-born physicist who had fled the Nazis and become an American citizen. A much smaller group knew of Einstein’s revolutionary assertion of the convertibility of mass to energy, quantified in the equation E = mc^2.
Smyth explained what the equation meant. “If this is stated in actual numbers, its startling character is apparent. It shows that one kilogram (2.2 pounds) of matter, if converted entirely into energy, would give 25 billion kilowatt hours of energy,” he wrote. “This is equal to the energy that would be generated by the total electric power industry in the United States (as of 1939) running for approximately two months. Compare this fantastic figure with the 8.5 kilowatt hours of heat energy which may be produced by burning an equal amount of coal.”
Before the outbreak of the present war, Einstein’s equation had been of theoretical interest primarily. But the demands of the war prompted pursuit of its practical implications. Einstein himself wrote to Franklin Roosevelt urging an effort to see if atomic energy could be put to military use. The result was the Manhattan Project.
Smyth’s report supplied readers a primer on the science behind the project: on atoms and their constituent parts, especially neutrons; on radioactivity elements and their isotopes; on nuclear binding energies and how they might be overcome; on the transmutation of one element into another; on chain reactions and the complicated pathways they followed.
Smyth described the experiments demonstrating that chain reactions—by which the splitting of one atom of uranium, say, produced neutrons that split other uranium atoms, which created more neutrons, and so on—were possible. This was a major step, but only a first one. “The technological gap between producing a controlled chain reaction and using it as a large-scale power source or an explosive is comparable to the gap between the discovery of fire and the manufacture of a steam locomotive,” Smyth wrote.
Yet the physicists thought they were on the right track. And they redoubled their efforts, lest the Germans be working in the same direction and get to the end first. “It was conceivable that a few uranium bombs might be decisive in winning the war for the side first putting them into use,” Smyth wrote. “Such thoughts were very much in the minds of those working in this field.”
Smyth and his colleagues were gathered at a single laboratory and cloistered for the duration of the project. “In the choice of a site for this atomic-bomb laboratory, the all-important considerations were secrecy and safety,” he explained. “It was therefore decided to establish the laboratory in an isolated location and to sever unnecessary connection with the outside world.” The site chosen was Los Alamos, New Mexico, an hour’s difficult drive northwest of Santa Fe.
Few of the Los Alamos scientists had worked on weapons before the war; they had thought of atomic energy mostly in peaceful terms. Now had to reset their aims. “In our earlier discussions of chain reactions, it was always taken for granted that the chain reacting system must not blow up,” Smyth said. “Now we wanted to consider how to make it blow up.”
It wasn’t easy. To be useful in a bomb, the chain reaction had to blow up atomically before it blew itself apart physically, scattering the material and causing the chain reaction to fizzle. But the scientists succeeded, to their great satisfaction.
Yet even before the bomb was used, Smyth and the others wondered what they had unleashed. “A weapon has been developed that is potentially destructive beyond the wildest nightmares of the imagination—a weapon so ideally suited to sudden unannounced attack that a country’s major cities might be destroyed overnight by an ostensibly friendly power,” Smyth wrote.
Monstrous weapons this had long been the stuff of science fiction, the work of arch-villains. But this weapon had been built by the good guys. “This weapon has been created not by the devilish inspiration of some warped genius but by the arduous labor of thousands of normal men and women working for the safety of their country,” Smyth observed.
They had been forced to their task by the dire risk America faced, Smyth said. “Before the surrender of Germany there was always a chance that German scientists and engineers might be developing atomic bombs which would be sufficiently effective to alter the course of the war. There was therefore no choice but to work on them in this country.” Speaking perhaps for himself but definitely for some of his colleagues, Smyth went on, “Initially many scientists could and did hope that some principle would emerge which would prove that atomic bombs were inherently impossible.” They had no such luck, and saw no choice but to press on.
Smyth’s report appeared before the Japanese surrender demonstrated how effective the atom bomb could be in breaking an enemy’s will. Yet he and the others were already looking beyond the current war to what would follow. “The future possibilities of such explosives are appalling, and their effects on future wars and international affairs are of fundamental importance. Here is a new tool for mankind, a tool of unimaginable destructive power. Its development raises many questions that must be answered in the near future.”
Heretofore the scientists and a small handful of political leaders had been the ones asking the questions. Henceforth the American people must bear the daunting responsibility. “These questions are not technical questions,” Smyth said. “They are political and social questions, and the answers given to them may affect all mankind for generations.”