themselves to ram the battleships if necessary, but nothing restrained their attack. At 0758 the Ford Island command center radioed its frantic message to the world: air raid pearl harbor, this is not drill. Admiral Kimmel saw the attack begin from a neighbor's lawn — “in utter disbelief and completely stunned,” the neighbor remembers, “as white as the uniform he wore.” Torpedoes struck a light cruiser and a target ship, a minelayer, another light cruiser, then the battleships:
The man who conceived and planned the surprise attack on Pearl Harbor, Admiral Isoroku Yamamoto, Commander in Chief of the Japanese Combined Fleet, had few illusions about the ultimate success of a war against the United States. He had studied at Harvard and served as a naval attachd in Washington and knew America's strength. But if war had to come he meant “to give a fatal blow to the enemy fleet” when it was least expected, at the outset. By that act he hoped he could win his country six months to a year during which it might establish its Greater East Asia Co-Prosperity Sphere and dig in.
The torpedoes had been a challenge. Pearl Harbor was only forty feet deep. Torpedoes dropped from planes routinely sank seventy feet or more before bobbing up to attack depth. The Japanese had to reduce that plunge signficantly or bury their weapons in the Pearl mud.
They found in repeated experiments that they could sometimes manage a shallower drop by flying only forty feet above the water and holding down their air speed — the maneuver demanded skilled flying — but further improvement required torpedo redesign, largely by trial and error. As late as mid-October Fuchida's flyers were still managing no better than sixty-foot plunges, still far too deep.
A new stabilizer fin, originally designed for aerial stability, saved the mission. Tested during September, it consistently held the torpedo to less than forty feet and steadied it as well. But the pilots still needed aiming practice. Only thirty of the modified weapons could be promised by October 15, another fifty by the end of the month and the last hundred on November 30, after the task force was scheduled to sail.
The manufacturer did better. Realizing the weapons were vital to a secret program of unprecedented importance, manager Yukiro Fukuda bent company rules, drove his lathe and assembly crews overtime and delivered the last of the 180 specially modified torpedoes by November 17. Mitsubishi Munitions contributed decisively to the success of the first massive surprise blow of the Pacific War by the patriotic effort of its torpedo factory on Kyushu, the southernmost Japanese island, three miles up the Urakami River from the bay in the old port city of Nagasaki.
13
The New World
Enrico Fermi's team at Columbia University had been hard at work through 1941 while the government deliberated. Fermi, Leo Szilard, Herbert Anderson and the young physicists who had joined them may never have known how close they came to orphanhood. The isolation of pluto-nium at Berkeley added a potential military application to their reasons for pursuing a slow-neutron chain reaction in uranium and graphite, but given the necessary resources Fermi at least would certainly have pursued the chain reaction anyway as a physical experiment of fundamental and historic worth. He had missed discovering fission by the thickness of a sheet of aluminum foil; he would not willingly leave to someone else the demonstration of atomic energy's first sustained release. Thanks largely to Arthur Compton his work found continued support, which may help explain why he admired the pious Woosterite's intelligence so extravagantly.
Szilard had finally gone on the Columbia payroll on November 1, 1940, when the $40,000 National Defense Research Committee contract came through for physical-constant measurements. To help Fermi without the friction the two men generated when they worked side by side, Szilard undertook to apply his special talent for enlightened cajolery to the problem of procuring supplies of purified uranium and graphite. The record is thick with his correspondence with American graphite manufacturers dismayed to discover that what they thought were the purest of materials were in fact hopelessly contaminated, usually with traces of boron. The cross section for neutron absorption of that light, ubiquitous, silicon-like element, number 5 on the periodic table, was tremendous and poisonous. “Szilard at that time took extremely decisive and strong steps to try to organize the early phases of production of pure materials,” says Fermi. “… He did a marvelous job which later on was taken over by a more powerful organization than was Szilard himself. Although to match Szilard it takes a few able-bodied customers.”
In August and September the Columbia team prepared to assemble the largest uranium-graphite lattice yet devised. A slow-neutron chain reaction in natural uranium, like its fast-neutron counterpart U235, requires a critical mass: a volume of uranium and moderator sufficient to sustain neutron multiphcation despite the inevitable loss of neutrons from its outer surface. No one yet knew the specifications of that critical volume, but it was obviously vast — on the order of some hundreds of tons. One way to create a self-sustaining chain reaction might be simply to continue stacking uranium and graphite together. But so crude an experiment, if it worked at all, would teach the experimenter very little about controlling the resulting reaction and might culminate in a disastrous and lethal runaway. Fermi proposed to approach the problem by the more circumspect route of a series of subcritical experiments designed to determine the necessary quantities and arrangements and to establish methods of control.
As always, he built directly on previous experience. He and Anderson had calculated the absorption cross section of carbon by measuring the diffusion of neutrons from a neutron source up a column of graphite. The new experiments would enlarge that column to take advantage of the increased stocks of graphite available and to make room for regularly spaced inclusions of uranium oxide: simplicity itself, but in physical form a thick, black, grimy, slippery mass of some thirty tons of extruded bars of graphite confining eight tons of oxide. Fermi named the structure a “pile.” “Much of the standard nomenclature in nuclear science was developed at this time,” Segre writes. “… I thought for a while that this term was used to refer to a source of nuclear energy in analogy with Volta's use of the Italian term
The exponential pile Fermi proposed to build (so called because an exponent entered into the calculation of its relationship to a full-scale reactor) would be too big for any of the laboratories in Pupin. He sought larger quarters:
We went to Dean Pegram, who was then the man who could carry out magic around the university, and we explained to him that we needed a big room. And when we say big we meant a really big room. Perhaps he made a crack about a church not being the most suited place for a physics laboratory… but I think a church would have been just precisely what we wanted. Well, he scouted around the campus and we went with him to dark corridors and under various heating pipes and so on to visit possible sites for this experiment and eventually a big room, not a
