released 01 jun 09 / last mod 01 jun 09 / greg goebel / public domain
* As the tide of the war turned decisively against the Axis, the Americans pushed forward on development of the atomic bomb. Physicists such as Leo Szilard and Neils Bohr began to raise questions about the issues posed by the atomic bomb; but they were effectively ignored by the authorities.
* As the US bomb effort ramped up, the Axis bomb effort was all but going in reverse, with Les Groves making sure that the German effort was given a kick in the teeth. The British had drawn up plans to sabotage the Norsk Hydro heavy-water plant in Norway; Groves requested action almost immediately on taking charge of the Manhattan Project, and the British complied. An assault on 19 November 1942 involved the drop of 34 Norwegian commandos in two gliders and ended in disaster: both gliders crashed and the Germans shot all those who survived, in accordance with a secret order issued by the Fuehrer in October to summarily execute all Allied commandos even if they were in uniform.
The British thought the matter over and decided to try again. On 16 February 1943, six Norwegian commandos were parachuted into Norway, to meet up with four other commandos who had been sent in earlier to make way for the failed assault in November. In a nighttime raid on 27:28 February, they infiltrated the plant's security perimeter, crept in through a drain, and planted charges to destroy the heavy-water production system. There were no casualties on either side in the operation; there was no way the plant would be producing heavy water again for a year.
In Japan, while physicist Yoshio Nishina worked on the atomic bomb for the Imperial Japanese Army, in July 1942 the Imperial Japanese Navy (IJN) set up a committee to secretly consider development of the atomic bomb. It deliberated into March 1943, to finally conclude it would take ten years for Japan to build an atomic bomb, and that nobody else was likely to be able to build one in the near future either. The committee disbanded, with the members going their separate ways, though a separate branch of the IJN continued to fund atomic bomb research at the University of Kyoto.
The IJN knew little or nothing of Nishina's work for the IJA -- the two armed services had a case of interservice rivalry that defies belief, fighting like "dogs and monkeys", as the Japanese say, on almost every issue. Nishina's work had progressed to the point where he had ideas on how to perform isotope separation on an industrial scale, at the very time Japan's war machine was starting to run out of resources.
* The fact of the matter was that the Axis was on the defensive. The Germans had suffered a major defeat at Stalingrad, with an entire German army encircled late in 1942 and wiped out a few months later. The Germans had then been run out of Africa, with large numbers of prisoners taken. The IJN had suffered a stinging defeat at Midway in June 1942, losing a good proportion of the service's vital aircraft carriers, and had been defeated in the battle for the island of Guadalcanal in the South Pacific. Now the Americans were poised to move against the island bases on the overextended perimeter of Japan's Pacific empire.
The brutality of the war was ramping up steadily. Intelligence was leaking out to the Allies about the mass exterminations of Jews and other "undesireables" in German death camps. The British had been conducting night bombing raids against Hitler's Reich; for want of better targeting accuracy, the raids deliberately and indiscriminately pounded entire cities. A series of massive raids in late July all but destroyed Hamburg, killing tens of thousands of civilians.
In the Pacific, there were relatively few civilians in the way, but as if to compensate the ground fighting was extremely vicious. The Japanese were not inclined to take prisoners, and a Japanese soldier usually preferred to kill himself up with a grenade rather than be taken prisoner himself; one would pretend to surrender and then blow up an American soldier along with himself. The Americans quickly got wise to this game and usually gunned down Japanese who appeared to be trying to surrender. When American bombers sank a Japanese troopship, they often came back and strafed the soldiers floundering in the water -- as if stepping on so many ants.
* While the Axis was giving up work on the atomic bomb, the Soviet Union was beginning to move forward on its own bomb development program. There had been some discussion among and lobbying by Soviet physicists roughly in parallel with similar efforts in the USA, and the Kremlin had become more interested in 1940 when fission-related work in the US and Britain simply disappeared from the scientific press. Papers from high-profile nuclear physicists and chemists suddenly ceased being published, which all but convinced the suspicious Soviets that something big was going on.
Nothing much serious had been done in the USSR when the invasion of the country in June 1941 suspended all work not immediately focused on the survival of the state. However, after the situation stabilized late in 1941, the Soviet government set up an advisory committee on atomic bomb development, including an ex-student of Rutherford's named Peter Kapitza and an influential physicist named Abram Joffe. The committee concluded that the Soviet Union needed to pursue atomic bomb research, and recommended that Igor Kurchatov, a robust Siberian who was one of Joffe's star proteges, be assigned to head up the effort. Kurchatov was reluctant to take the job, believing that it would be wiser to focus on short-term research efforts in order to defeat the Germans, but he was persuaded to take charge.
* While the struggle went on at the front lines, the physicists at Los Alamos focused on building the atomic bomb, wrestling with a seemingly endless list of theoretical and practical details. Enthusiasm was high; Oppenheimer later recalled Fermi telling him: "I believe your people actually want to make a bomb." Fermi found the idea distinctly appalling.
Work went ahead on the implosion bomb and gun-type bomb designs. The implosion bomb acquired the name of "Fat Man" because as it emerged it looked like an egg with box tailfins. Implosion was extremely tricky, requiring all the fissile segments to be blasted together with absolute precision. The technical boss on the design was Seth Neddermeyer, one of Oppenheimer's graduate students; the challenge was formidable, mocked by its critics as like trying to crush a beer can while keeping all the beer inside. Neddermeyer got help from John von Neumann, another of the Hungarian expatriate physicists, a brilliant theoretician who visited from Princeton.
The gun-type bomb had its own difficulties. Originally, the assumption was that it would have to be built around the barrel of an artillery piece, which resulted in a huge weapon, known as "Thin Man". As it turned out, since the gun was only going to be fired once, there was no need to build it like a real artillery piece. Gradually the design of the gun-type weapon converged on a more convenient device, which became known as "Little Boy".
In either case, the delivery system was going to be the Boeing B-29 Superfortress bomber -- the US Army Air Forces (USAAF) didn't have any other bomber big enough to handle either Fat Man or Little Boy. The four-engine B-29 was to be one of the most advanced aircraft of its era, capable of carrying a huge warload high, far, and fast. It was a high-priority project, funded at roughly the same level as the atomic bomb effort. For the moment, work on the Superfortress was not going smoothly -- the first prototype had caught on fire in February and crashed into a meat-packing plant in Seattle, killing all its crew and dozens of workers on the ground. Boeing engineers worked overtime trying to get the B-29 to fly right.
* The obvious critical path in the construction of an atomic bomb was to obtain fissile material. The appropriate "weapons grade" materials could be produced in principle by separating the traces of fissile uranium-235 from the much more common uranium-238, or by synthesizing fissile plutonium-239 from uranium-238 in what would eventually be known as a "breeder reactor".
While the Los Alamos site had been growing up out of the ground in New Mexico, under the overall direction of boundlessly energetic Les Groves, a facility at least as impressive had been put together in the mountains of east Tennessee to separate uranium-235 from uranium-238. The site was alongside the Clinch River and was given the cover name of the "Clinton Engineering Works", after a nearby town -- but it was more generally known as "Oak Ridge" after a local landmark. Construction had begun in the fall of 1942 and by 1 April 1943, the Oak Ridge site was ready for business.
There was a debate over the best way to separate uranium-235 from uranium-238. Ernest Lawrence preferred "electromagnetic separation" -- in essence, using a battery of modified mass spectrographs to do the job. The modified mass spectrographs were named "calutrons", after the University of California at Berkeley ("Cal-U"). It wasn't going to be an easy job, with Lawrence estimating that 2,000 calutrons would be needed to acquire a mass of uranium-235 adequate for a bomb in less than year. Others promoted separation by gaseous diffusion, and Lawrence didn't object: no industrial-scale separation method had been implemented to that time and there was no reason to bet the farm on any one scheme.
Les Groves hedged his bets and implemented both electromagnetic separation and gaseous diffusion systems. One of the problems with building the calutrons involved their electromagnets -- they required metal for windings and copper was in short supply. The US Treasury Department came to the rescue, having offered to supply silver bullion to make wire, as long as the silver was given back in the end. The Army took up the offer, though when the officers involved told a Treasury official that thousands of tons of silver would be required, the official replied: "Colonel, in the Treasury we do not speak of tons of silver. Our unit is the troy ounce." The Army got the silver and Groves made sure it was meticulously accounted for.
Obtaining the metal for the windings turned out to be relatively straightforward, but the early calutrons shorted out easily, requiring a troublesome redesign. Building the gaseous diffusion system at Oak Ridge wasn't easy, either, particularly since the uranium hexafluoride gas was, as noted, hideously corrosive: the diffusion barrier had to be made of nickel and fabricated with a new process, while the seals in the piping had to be made of a new fluorine-based plastic that would eventually be known as "teflon". Any one stage of gaseous diffusion produced only a slight enrichment, so the diffusion system involved massive numbers of stages and a maze of piping.
The Oak Ridge plant ended up becoming a huge installation, with Ernest Lawrence being absolutely astounded by it during a visit in May 1943. However, by the end of 1943, fissile material was still not coming off the production line in any quantity. Groves wasn't happy, and when he wasn't happy nobody who worked for him was, either.
* Groves was not ignoring the option of breeding plutonium in a reactor, but there was no way to do that at Oak Ridge. A catastrophic failure of a breeder reactor would not only threaten the nearby city of Knoxville, but it would also shut down the rest of the Oak Ridge facility. An isolated site elsewhere was required.
It was found in the state of Washington, in the Northwest USA. Washington is stereotyped as damp and rainy, but that is only true of the western part of the state. The Cascade mountain range blocks much of the rainfall into the interior and central Washington is dry, an underpopulated sagebrush desert. The mighty Columbia river twists south through the center of the state, finally turning westward to flow to the sea and establishing much of the border with the state of Oregon to the south.
The isolation of the area and the availability of the Columbia's water for cooling made the region an ideal site for a breeder reactor. A tract of ranchland near the little town of Hanford, on a kink in the Columbia just before it turned west, was duly purchased and construction begun immediately. A team under Eugene Wigner came up with a design for a water-cooled breeder reactor. It took some time to get work started -- unsurprisingly, there was a labor shortage and most available workers weren't keen on moving out to some barren desert where the summers were hot and sandstorms common. Those who did come found entertainments hard to come by in their free time, resulting in drunkenness, fights, and the occasional murder. Problems were dealt with, and by the summer of 1943 the facility was beginning to rise out of the desert.
* By that same summer, in the Soviet Union Igor Kurchatov's atomic bomb research team had moved from the halls of academia to a dedicated research facility on an abandoned farm on the Moscow River. There were only about twenty researchers at "Laboratory Number 2", and they were focused on preliminary studies. The USSR was not quite ready to move forward on full development of the atomic bomb.
* Les Groves not only had to deal with a long list of technical issues, he also had to ride herd on a gang of physicists, not all of whom were sufficiently submissive for his taste. The most significant case in point was Leo Szilard, who did not like the way atomic bomb development was under strictly military control and had not hesitated to say so. Later Groves would describe Szilard as: "The kind of man that any employer would have fired as a troublemaker."
This remark said more about Groves' arrogance than it said much about Szilard, with Groves casting Szilard in the role of a loose-cannon employee instead of the person who, more than any other one individual, was the father of America's atomic bomb program. In the fall of 1942, there had been a bureaucratic squabble between Groves and Szilard, leading to Groves toying with the idea of interning Szilard as an enemy alien. Compton interceded, smoothing over the trouble. Compton then passed up to Groves documents that Szilard had provided on his efforts to push atomic bomb research in 1939 and 1940, as well as Szilard's early attempts to shut down publication of nuclear research papers. Groves went quiet for the moment, but he was by no means reconciled to Szilard.
Szilard's pioneering work in atomic power also gave him some patents that he was able to use to make the authorities -- meaning Groves in particular -- uncomfortable. The patent issue did involve royalty payments, but Szilard mainly saw it as a lever to ensure that his voice was heard. Groves found Szilard so annoying that, despite the fact that Szilard was Jewish, the general even suspected the scientist was a Nazi spy. By the spring of 1943, Army Intelligence was tailing Szilard full-time. The intelligence people found their target amusing, an absent-minded sort, with an extensive social network of Jewish friends and many contacts with influential government officials. They reported there was absolutely no evidence that Szilard was anything but what he seemed to be.
Groves remained suspicious, repeatedly trying to pressure Szilard into signing a security pledge. Szilard repeatedly gave verbal assurances about his commitment to security and refused to sign. By the end of the year, the patent issue had been resolved, with the Army reimbursing Szilard for $15,416.60 for his unpaid work at Columbia in the time leading up to the establishment of the Manhattan Project. Szilard, however, still felt the need to make his views on the political implications of the atomic bomb known.
Szilard had been at the forefront of pushing the development of the atomic bomb, and remained at the forefront of raising concerns about its implications. There were good reasons for concern, since the bloody-mindedness of the war was continuing to spread, even among Los Alamos staff. In May 1943, following up some discussions among Met Lab staff, Enrico Fermi conducted a study on the possibility of dusting German food supplies with radioactive isotopes. The study concluding that the dusting could kill up to a half million Germans; Fermi was no longer as easily appalled as he had been. Oppenheimer conditionally gave his blessing to the idea, though it was really just a long-shot backup plan in case atomic bomb development went off track. It also raised the possibility that the Germans might try the same stunt. A number of US Army officers were sent to England with geiger counters and the appropriate training to provide a warning capability.
* By that time, Szilard wasn't the only voice raising concerns over the atomic demon. The Nazi leash on Denmark had been loose up to the summer of 1943; Hitler had no particular issues with the Danes, and Denmark was an agricultural powerhouse, helping keep Germany fed. Even Danish Jews were generally left alone. However, by early 1943 tensions between the Danes and the occupying power were on the increase, aggravated by the fact that the writing was beginning to appear on the wall for Hitler's Nazi empire. His weak-tea Fascist ally Mussolini resigned and was arrested on 25 July, an act that was soon followed by the surrender of Italy to the Allies.
On 28 August, the German occupation authorities demanded that the Danish government take harsh measures to suppress civil unrest. The king and the government refused, and Denmark was reoccupied the next day. The Germans planned to deport the 8,000 or so Danish Jews to death camps in late September, but in one of the stranger stories of the war a German officer tipped off the Danish authorities about the raid, and the Danes hid away most of the Jews. The officer in question had a long history of human-rights abuses and it is generally thought he had a less than altruistic motive in tipping off the Danes, but nobody's sure of exactly what it was.
There was also to be a roundup of prominent and defiant Danes, with Niels Bohr near the top of the list. On 29 September he and his wife Margrethe took a motorboat ride to Sweden; their sons would follow later, with the family settling in Stockholm. There he appealed to the Swedish government to offer to take in Denmark's Jews, and on 2 October the Swedes broadcast an offer of asylum over the radio, with the Jews taking up the offer.
Stockholm was rotten with Nazi agents and there were fears for Bohr's safety. Word of his escape from Denmark had got back to Britain, and Lord Cherwell sent an invitation for him to come to the UK, which was accepted. Given that the Axis effectively surrounded Sweden, physical communications between Britain and Sweden were by twin-engine British Mosquito light bombers, which could fly fast and high, avoiding interception while they carried small cargoes of mail and precision Swedish ball bearings. They could also carry a passenger in the bombbay, which was fitted up to make it as comfortable as possible under the circumstances.
There was no way that Bohr could take his whole family with him. On 6 October 1943, Bohr flew the "ball bearing express" to the UK, wearing a flight suit and an oxygen mask. He had some difficulties with the oxygen mask and passed out. The pilot was keeping tabs on his passenger via an intercom, and when no answers were forthcoming from the bombbay, the flight crew took the aircraft down to lower altitude; Bohr arrived in Scotland unharmed. His son Aage, also a physicist, flew in a week later.
James Chadwick briefed Bohr on the progress in the atomic bomb program, which astounded Bohr. Bohr had a few surprises of his own for the British as well, showing them the sketch Heisenberg had drawn of a heavy-water reactor. Those who knew what it might represent were startled, and had also received intelligence that the Norsk Hydro plant in Norway was back in operation. The USAAF hit the plant with 140 Boeing B-17 Flying Fortress bombers at mid-day on 16 November. The bombs were off target; still, they destroyed some of the plant support facilities and shut it down. The Germans contemplated relocating heavy water work to a more secure site in Germany, but the Norwegian resistance movement was keeping an eye on matters. A few months later, in February 1944, the Germans tried to ship out such stocks of heavy water as had been accumulated at the plant -- but the resistance sank a ferry carrying the barrels, with dozens of Norwegians drowning in the sinking. The German atomic research effort then came to an effective halt.
By that time Neils Bohr and his son Aage were at Los Alamos, on the British payroll along with a gaggle of other researchers, including James Chadwick, Otto Frisch, Rudolf Peierls, and yet another German physicist, named Klaus Fuchs. Fuchs was a very precise man, who Peirels' wife Genia nicknamed "Penny-In-A-Slot" since he would only speak when spoken to, responding to a question after a moment's thought with a neatly-thought-out and articulate answer. He would end up playing a far more significant role in the program than anyone on the Manhattan Project conceived at the time.
In any case, Churchill wanted Britain to maintain a partnership in the atomic bomb program and the British team was accepted into the fold. The expatriates found the USA full of luxuries unheard-of in wartime Britain; exactly what they thought of the arid open spaces of New Mexico after living in the damp green hills of England was less clear.
* The Bohrs had been named "Nicholas & James Baker" by Army security; they were referred to as "Uncle Nick & Jim" by the Los Alamos staff. The staff were also extremely interested when Bohr showed them Heisenberg's sketch of a heavy water reactor. It didn't look like a weapon, but Oppie was nervous enough to set up a committee to investigate if such a reactor could be used as one. The conclusion was that device built on such principles would be no more effective than a TNT bomb of the same size.
Although the rest of the British team set up home at Los Alamos, Bohr was merely a tourist, saying later: "They didn't need my help in making the atomic bomb." His concern, much like Szilard's, was simply how it would be used, what arrangements would be made in the postwar period to ensure that the bomb stayed under control. On arrival in the US in Washington DC that December, Bohr had met up with Supreme Court Justice Felix Frankfurter, the two having met in 1933 in London as part of the effort to rescue exiled German scientists. Frankfurter was a Vienna-born secular Jew who was a long-time advisor to Franklin Roosevelt; the physicist and the justice didn't have much time to chat at the time, but when Bohr returned to Washington DC in mid-February, he looked up Frankfurter in hopes of opening a channel to Roosevelt.
There was the problem that Frankfurter was not cleared on the Manhattan Project, but Frankfurter was able to second-guess Bohr's intent to a degree. Frankfurter had a vague knowledge of a "significant" military program that he just referred to as "X" and had something to do with physics, and the two men were able to chat in general terms about "X" without focusing on any details. When the two men met again in late March, Bohr learned that Frankfurter had indeed discussed matters with the president, who told the justice that he was "worried to death" over the matter and was "eager" to discuss "proper safeguards".
All this sounded promising, but the British were the key partner in the atomic alliance, and it wasn't a question of the Americans just making decisions on their own -- the British had to be in the loop, all the more so because Bohr was in the USA under British sponsorship. Roosevelt made it clear that Bohr had to discuss matters with Churchill to get things rolling. In early April, Niels Bohr and his son flew to Britain in a military aircraft, to find Churchill in no particular hurry to discuss things. Bohr went to Number 10 Downing Street on 16 May, escorted by Lord Cherwell, to talk with Churchill, who became downright hostile: "He scolded us like two schoolboys!" -- as Bohr described it later. Churchill had no patience with highflown ideas about the postwar control of the atomic bomb, saying: "After all, this new bomb is just going to be bigger than our present bombs. It involves no difference in the principles of war. And as for any post-war problems, there are none that cannot be amicably settled between me and my friend, President Roosevelt."
* Bohr persisted in his efforts, but his work on the politics of the atomic bomb had reached a dead end. Although Churchill wanted to keep the bomb an Anglo-American monopoly, Bohr and others knew that once the atomic bomb had been unveiled, others would soon have it -- and it wasn't really like any other bomb, merely bigger, it was a weapon that could shatter civilization, even exterminate humanity.
The conclusion of the war was not in doubt by that time. On 6 June, an Allied force landed on the beaches of Normandy, and soon Hitler's Reich would be squeezed in a vise between the Soviets and the Western Allies. In the Pacific, the Allies were methodically grinding down Japan's outposts, capturing strategically important islands and letting the others rot in isolation. The assault on the Marianas, on Japan's inner defensive ring, began in mid-June, resulting not only in the loss of an important Japanese outpost but in the effective crippling of Imperial Japanese Navy air power.
The ground fighting in the Marianas had been vicious, but that had been expected. What had not been expected was the fact that tens of thousands of Japanese civilians on the island of Saipan, believing propaganda that they would be abused by the Americans, threw themselves over the cliffs into the sea. The demonstration that the Japanese preferred death to surrender suggested that bringing the war in the Pacific to a successful end might be even more difficult than had been believed.
In late June the Bohrs went back to Washington DC, to sweat in the sticky heat of the summer there. Having gone nowhere in London, Bohr worked to retrieve the situation by writing an extended memorandum to Roosevelt. In the memorandum, Bohr emphasized that atomic bombs were not like other weapons, that once nuclear weapons were in widespread service, nobody would be able to win an all-out war. The only result would be mutual destruction. To build up massive stockpiles of nuclear weapons would decrease security because it would give a nation an incentive to strike first before it was destroyed itself. Bohr advocated a program of arms control, with limits set by nations on the production and deployment of atomic weapons, and verification schemes implemented to ensure that nobody cheated.
Frankfurter passed the memorandum along to Roosevelt on 5 July. The president met with Bohr privately on 26 August and seemed very enthusiastic about Bohr's ideas, even giving Bohr the impression that the Dane might go to the Soviet Union for discussions. However, once again Roosevelt was a politician, and being agreeable didn't imply any commitment. In late September, Roosevelt met with Churchill in Quebec -- to emerge from the meeting in step with Churchill's negative attitude towards arms control. In fact, when Churchill heard that Bohr was extending feelers to Soviet physicists, Churchill found this treasonous, complained that the exchange between Bohr and Justice Frankfurter was a serious breach of security, and suggested Bohr ought to be arrested. Roosevelt was never as blunt as Churchill but was in agreement with him in principle. Bohr's efforts were effectively at an end.
* Incidentally, in the wake of the Normandy invasion, a special force set up by Groves late in the previous year and codenamed ALSOS went into operation. Its mission was to obtain intelligence on the German atomic bomb program. Somewhat puzzlingly, despite the fact that Szilard and many other physicists had been warning about the Nazi nuclear effort well before America entered the war, no specific intelligence program had been set up to find out what the Germans were up to -- and in fact Groves only set up ALSOS when General Marshall, chairman of the joint chiefs, asked him to. It seems that Groves feared an intelligence effort might cut both ways: those working in such an effort would have to be briefed on essential details of the American program in order to know what to look for, and if they were captured it might compromise Los Alamos' security. Somewhat uncomfortably, the codename ALSOS turned out to mean "grove" in Greek, which Groves thought was too big a clue -- but changing it would draw more attention to the matter and so it stayed as it was.
ALSOS was under the direction of Lieutenant Colonel Boris Pash, an Army security man, with a past history as an FBI-trained Red hunter. Pash was competent and energetic, though a bit paranoid: he was among those who were convinced Oppenheimer was a Red spy. ALSOS was only supposed to follow the troops, but Pash and his men turned out to be willing to move ahead of the battle lines when they thought an opportunity justified it.
* While Niels Bohr shuttled back and forth across the Atlantic on his dead-end mission, the researchers at Los Alamos were accelerating towards the goal of building the atomic bomb. Continued analyses showed that the atomic bomb was practical and the effort was on track. It turned out that plutonium wouldn't work in the gun-type bomb: plutonium went "critical" faster than uranium-235, and there was no way to shoot the slug into the core fast enough to keep the weapon from "pre-igniting", resulting in a fizzle. Work on the plutonium bomb focused on the implosion scheme, though it was clearly a challenge.
As far as the problems with uranium enrichment went, potential salvation appeared in the form of a scheme that Philip Abelson had devised for the US Navy known as "thermal diffusion". When a mix of isotopes was placed in a thermal gradient, lighter isotopes tended to migrate towards the cooler end of the gradient, while heavier isotopes tended to migrate towards the hotter end of the gradient. Abelson came up with a thermal diffusion separation system that involved three nested pipes, stood vertically: the inner pipe was filled with hot steam, the middle pipe was filled with liquid hex, and the outer pipe carried cooling water. The arrangement set up a convection current in the hex, with enriched material being siphoned off the top.
The basic concept had actually been invented in Germany before the war, but Abelson was the first to come up with an implementation appropriate for large-scale use. It was a relatively cheap process, useful for high-volume production of enriched uranium, but it had two drawbacks: it required huge amounts of steam, and it couldn't enrich uranium enough to permit its use in a bomb. It was for precisely these reasons that the Manhattan Project had rejected the approach early on. The Navy hadn't worried much about these problems because the service was used to working with large volumes of hot steam in the turbine propulsion systems of warships, and was also mostly interested in using atomic power to drive submarines. Bomb-grade enrichment wasn't needed for a power reactor.
Oppenheimer had seen a report on Abelson's work in early 1943 and not been impressed, but in the spring of that year Oppie had a brainstorm: even if thermal diffusion couldn't enrich uranium up to bomb grade, it could be used to obtain large quantities of partly-enriched uranium that could be then put through calutrons to complete the enrichment. Oppie did some simple calculations and came to the conclusion that such a "two-stage" process would easily put an end to the enrichment bottleneck. Oppenheimer felt stupid, telling Groves: "We've made a terrible scientific blunder." Groves had already been siphoning output of the gaseous diffusion system at Oak Ridge into the calutrons as a stopgap solution. Now a two-stage solution based on thermal diffusion and the calutrons offered a real fix. In mid-June, Groves ordered the construction of a thermal-diffusion separation plant at Oak Ridge, using Abelson's design exactly as it was, there being no time to tinker with it.
* Fueling of the three breeder reactors at Hanford began in mid-September 1944, with Enrico Fermi -- now an American, he and his wife having been granted citizenship in July -- doing the honors of inserting the first aluminum-canned natural uranium slug into a reactor core. Loading went on around the clock, but the slugs came in faster than they could be inserted. They were carried in wooden blocks and the blocks had to be stacked up. Leona Marshall, one of the site managers, joked with Fermi that the stack of blocks looked like an atomic pile. Fermi gasped and went pale, but after snatching his slide rule out of his pocket and fiddling with it for a moment he relaxed, realizing that a chain reaction in the stack was comfortably well outside the bounds of theoretical limits.
The first pile went online on 26 September 1944. All went well at first, but then the pile simply bogged down gradually and turned itself off. Fermi suspected that some product of the reaction was "poisoning" it. To lend weight to this suggestion, the pile later came back on, only to shut itself off again. It seemed that the reaction produced a short-lived product that absorbed neutrons, shut down the chain reaction, and then decayed, allowing the chain reaction to begin again, producing the poison until the pile died out once more.
Analysis confirmed the notion, showing the problem to be xenon-136 gas. Fortunately, a Princeton physicist named John A. Wheeler had worried about the possibility of fission-product poisoning and had suggested changes to the pile design to compensate. Although the modifications were expensive and time-consuming the contractor, Du Pont, had implemented them. Instead of rebuilding the piles, all that had to be done was change operational procedures to exploit Wheeler's additions.
Since the slugs produced by the breeder reactors only consisted of about 250 parts per million of plutonium, that meant separation was an issue, and a really nasty issue because much of the rest of the material in the slugs was hideously radioactive. The separation facilities used to extract plutonium from the slugs were major installations in themselves. Three were built, all consisting of huge sealed rectangular thick-walled concrete structures known as "Queen Marys" for their size. The separation process had been developed by Glenn Seaborg and his team, involving dissolving the slugs in nitric acid, precipitating the useful fraction, and then using centrifugation to concentrate it. Once the process had begun, nobody could get into one of the Queen Marys and live for very long, so the process was handled by remote control -- a remarkable feat given the technology of the time.
The separation plants began to go into operation late in 1944. By February, all three Hanford piles and the separation facilities were operating at full bore. Groves was relieved that things were finally on track, telling General Marshall that the US would have as many as 18 plutonium bombs available by the second half of 1945.
Although Edward Teller had made his ideas about the "super bomb" known, to his disappointment there was no interest in pursuing the concept for the moment. Get the atomic bomb working first, the thinking went, and then worry about the "super" later. Teller chafed at what he saw as a lack of vision, and also was frustrated at the fact that he hadn't been made head of the Theoretical Division at Los Alamos -- that job went to Hans Bethe.
* Everyone at Los Alamos was putting in long hours to get the atomic bomb built, though they still had time for some entertainment, including dorm parties, poker sessions, square dances, and amateur theatre. Oppenheimer didn't have much time to participate in anything that required any real effort, but he did make showings -- surprising the audience for the play ARSENIC & OLD LACE by being dragged out as a corpse. It didn't require learning much in the way of dialogue. There was a small, low-power broadcast station on the site, specializing in classical music, drawn from the collections of many of the staff, including Oppenheimer. There were occasional live performances of piano and the like from musically-inclined researchers, who were only introduced by their first names. There was fishing and hiking -- the daily bulletin was careful to warn that bears encountered on trails were not "tame bears like those in Yellowstone Park."
In fact, some of the European-born were not at all familiar with the threats posed by local wildlife. Sometime earlier, while Niels Bohr was visiting, he went on a hike with the Fermis and ran into a curious badger-like creature with black fur and white stripes down its back. Bohr found the beast intriguing and imprudently did not back up immediately, but it seems the skunk did not regard him as a threat, sparing the Nobel prize winner the indignity of having his clothes burned while he scrubbed himself down with tomato juice.
One of John Wheeler's proteges, a Jewish kid from Long Island named Richard Feynmann, brilliant and an egotistical smartass, amused himself the dorms by playing bongo drums -- though in the weekends he would drive off to a New Mexico sanitarium where his young wife was slowly dying of tuberculosis. He also claimed later to have picked up the hobby of cracking safes to test security, much to annoyance of the military authorities. There were amusements between the sheets as well, resulting in a flood of pregnancies and babies, straining the outpost's facilities to the extent that Groves tried to order it stopped. He was exceeding his authority and the order was ignored, even by his trusted technical director. In December 1944, Kitty Oppenheimer gave birth to a daughter, Katherine (who would in practice be called Toni).
Not all were able to cope with the isolation of the site. Kitty Oppenheimer began to drink heavily and gradually dropped out of leadership of social activities. Along with the pressures of his job and a troublesome family situation, Oppie was also continually grilled by Army security folks, who remained suspicious of his left-leaning activities before the war. There were some among them who were convinced he was a Red spy. They were looking in the wrong place, but under pressure Oppie lied to help protect those close to him. All his answers were recorded and filed; whether he realized it or not, whether he liked it or not, he was building up a potential brief against himself.
* By the spring of 1944, the aircraft designated to be the atomic bomb's delivery system, the B-29 Superfortress, was in production. It was suffering badly from teething problems, particularly a tendency of its powerful air-cooled piston engines to catch on fire. By the summer of 1944, it was performing strikes against Japan, though the task was proving difficult. Although the B-29 had very long range, the only way to mount attacks against the Japanese home islands at that time was from American bases in China. The Superfortress bases of the USAAF 20th Bomber Command in China were supplied by airlift over the Himalayas, a cumbersome process that demanded about seven supply flights for each individual bomber sortie. The results of such strikes on Japan as could be performed on this basis were very mixed.
In late August 1944, Major General Curtis LeMay arrived to take command of the 20th. LeMay was a tough, ruthless, extremely competent officer who like to chew on a cigar and was nicknamed "Iron-Ass LeMay" for his hardnosed approach to doing things. He was also smart enough to know that the position of the 20th in China was logistically preposterous, and that the Superfortress raids from China were a ridiculous way to fight a war.
The USAAF planned to pull the plug on Superfortress operations from China. The fall of the Marianas had given the USAAF a better base from which B-29s could attack Japan, and the USAAF gradually began to shift the focus from China to the Pacific. On 24 November 1944, B-29s from Tinian in the Marianas performed their first raid on the Japanese home islands. Results of that raid and those following were mixed; the B-29 was still not living up to its promise.
Back in the USA, a specially modified B-29 had performed the first drop of a dummy atomic bomb, a model of a Little Boy, on 3 March 1944. There were some problems with the initial tests, but in August 1944, the USAAF ordered 17 B-29s with the appropriate modifications for atomic bomb delivery, and by September 1944 the 393rd Bombardment Squadron was training for the mission at Wendover, in Utah. The operation was codenamed SILVERPLATE and had the highest priority for resources.
The 393rd was under the command of Lieutenant Colonel Paul W. Tibbetts, a reserved, cool, highly professional pilot with an outstanding service record. He had just finished an assignment as a test pilot for the B-29 and was very familiar with the aircraft. Tibbetts was the only person in the 393rd who had been briefed on the atomic bomb, but aircrews suspected they were going to be carrying a warload unlike any other when their training emphasized placing the Superfortress in a dive after bomb release and exiting the target area as fast as possible. They dropped "Pumpkins", which were rough facsimiles of the Fat Man bomb produced by Groves' organization, filled with concrete or high explosive.