A CHAIN REACTION
Seventy-five years ago, Col. Paul Tibbets flew the plane carrying the first weapon of mass destruction, an atomic bomb that would shortly bring World War II to a close. ¶ After dropping it over Japan, he turned the B-29 around for a look at the destruction before his return trip to a U.S. base on a Pacific Ocean island. ¶ “The sight that greeted our eyes was quite beyond what we expected, because we saw this cloud of boiling dust and debris below us with this tremendous mushroom on top,” Tibbets later recalled in an interview for the Manhattan Project Voices oral history archive. “Beneath that was hidden the ruins of the city of Hiroshima.”
That towering cloud marked Aug. 6, 1945, as America’s victory in a frenzied arms race that began when Albert Einstein wrote to President Franklin Delano Roosevelt six year earlier. A pair of German chemists had split the uranium atom, setting American scientists to fearing that Adolf Hitler and the Third Reich might be en route to an atomic bomb.
“A single bomb of this type, carried by boat and exploded in a port, might very well destroy the whole port together with some of the surrounding territory,” Einstein wrote. “However, such bombs might very well prove to be too heavy for transportation by air.”
Alexander Sachs, an economist friend of FDR’s, read Einstein’s letter to the president. FDR interjected: “Alex, what you are after is to see that the Nazis don’t blow us up.” Then FDR summoned a senior aide and told him: “This requires action.”
The route of America’s effort to beat Hitler to the bomb ran underneath the stands of the University of Chicago’s football stadium, as the Tribune revealed years later, in the days after the dropping of the second atomic bomb on Nagasaki, Japan, on Aug. 9, 1945.
A squash court under Stagg Field’s stands was available for the covert operation, the university having given up football. It was an appropriate site in 1942 for initiating the Manhattan Project, the crash course that the Roosevelt administration had decreed, and Enrico Fermi, an Italian physicist, was the logical choice to determine whether an atomic bomb was possible.
Fermi had pioneered the method by which the German chemists split the atom: bombarding uranium with subatomic particles called neutrons. Fermi thought he had produced a new element, but when the Germans bombarded uranium, they found it had been split. Yet the combined mass of the pieces was less than that of the uranium they started with.
The missing mass had been converted into energy. Expand the amount of uranium used, and the energy released would be the towering mushroom cloud that Tibbets saw. Without realizing it, Fermi had discovered nuclear fission.
A colleague on the Manhattan Project told the Tribune that Fermi was glad he misinterpreted his uranium experiment. Had he gotten it right, Hitler would have had an earlier start on a bomb.
Fermi realized a corollary of nuclear fission. Under certain conditions, a uranium atom might release a neutron that would knock two neutrons out of another atom. Those two would release four more, and so on, “after the fashion of firecrackers exploding in sequence,” the Tribune wrote.
To test the chain reaction theory, Fermi and his associates laid layers of graphite blocks, some encasing uranium, on the floor of the U. of C.’s squash court. Graphite would slow down neutrons and prevent them from flying off without striking a uranium atom. Holes were drilled in the blocks for cadmium rods. Inserted, the rods would freeze the chain reaction, and when removed, the reaction proceeded.
“The trick was to achieve a chain reaction but not one that would run dangerously out of control,” James Sturm, a graduate student who worked on the 20-foot-tall pile, told the Tribune in 2012. If something went wrong, graduate students would pour a neutron-absorbing liquid on the pile from a scaffold.
On Dec. 2, 1942, Fermi ordered the cadmium rods pulled out a little bit, and a Geiger counter clicked a few times. Pulled out farther, the clicking went on longer. When the rods were removed, the clicks blended into a sound like a drum roll.
“The pile has gone critical,” Fermi said. The reaction was self-sustaining.
Those present drank Chianti out of paper cups and signed the bottle. Arthur Compton, a U. of C. physics professor, called James Conant, the government’s czar of wartime research. They spoke in an improvised code:
“Jim, you’ll be interested to know the Italian navigator has just landed in the New World.” “Were the natives friendly?” “Everyone landed safe and happy.”
The decision had already been made that the atomic bomb would be manufactured in a rural stretch of western Tennessee. Designated “Site X,” it quickly became Oak Ridge, a city of 30,000 — designed and constructed under the strictest security. The architects of Chicagobased Skidmore, Owings & Merrill had to draft a master plan without knowing where it would be built. Oak Ridge’s curving roads, dotted with clusters of single-family homes, would become a template for the postwar suburban building boom.
By spring 1945, a prototype bomb was ready to be tested at a site near the Manhattan Project’s New Mexico facility in Los Alamos. Fermi had moved there and was close to his research assistants, Joan Hinton and Robert Carter. But they were too low on the totem pole to be invited to join Fermi and J. Robert Oppenheimer, the project’s scientific director, on the viewing stand. So on July 16, 1945, they rode Carter’s motorcycle toward the test site, a bowl-shaped valley surrounded by hills.
“Then, all of a sudden, the whole world lighted up, it seemed,” Carter told the Manhattan Project Voices. “When the shock wave came it was surprising and startling to us, and it was very, very loud. … It just rumbled back and forth around in this big valley.”
While the bomb was being built, Col. Tibbets and a team of engineers stripped a B-29 of every ounce of expendable weight. Einstein was right: At 9,700 pounds, the bomb was almost too heavy to be flown.
When President Harry Truman announced Hiroshima’s bombing, the Tribune reported that the “power of the universe” had been used to create a weapon that purportedly would make the U.S. “invulnerable to attack.”
Some scientists felt the bomb’s fearsome force should have been demonstrated to the Japanese by exploding it in an unpopulated area. And that question has been raised on each anniversary of the bombing of Japan.
Critics underline the fatalities. As many as 80,000 died instantly at Hiroshima, and at least 40,000 at Nagasaki, with tens of thousands dying afterward from the trauma. A wire story published in the Tribune later that August touched on the severity of the suffering of those who were lingering: “A Tokyo reporter was quoted as saying that many patients, in pain, shouted, ‘Please kill me, quick!’ ”
But shortly after Japan admitted to defeat that month, a Gallup Poll found that 85% of Americans approved of the dropping of the atomic bombs.
After Hiroshima was attacked, a Tribune reporter in the Philippines encountered GIs who would’ve taken part in an invasion of Japan if the nation hadn’t later announced its surrender. They were killing time, talking about women and passing around a newspaper account of the bomb.
“Some giant new force has been turned loose on the world and you wonder where it’s going to end,” one GI said, troubled.
“But the information in the (newspaper) was sketchy,” the reporter noted, “and after every one had read it, the paper was tossed aside, the veterans who had shot and been shot at put the information in the back of their heads where it could be pondered and worried over from time to time, and the talk went back to women.”