released 01 jun 09 / last mod 01 jun 09 / greg goebel / public domain
* After a period of indecision, the Americans finally committed to building an atomic bomb and the program began to gear up, resulting in the creation of a research facility at Los Alamos, New Mexico. Ironically, during the same period the Nazis effectively gave up on their atomic bomb program.
* In the UK, work on the atomic bomb was moving much more decisively, thanks to Prof Lindemann -- now Lord Cherwell, having been granted a baroncy through the good offices of Winston Churchill. Cherwell rendered the MAUD report down to a brief memorandum for Churchill, only two and a half pages long -- that was still much longer than the prime minister liked, but Cherwell knew the matter was important, and recommended action in relative detail. Churchill gave the go-ahead for further action on 27 August 1941; the British chiefs of staff added their assent on 3 September.
In the meantime, Mark Oliphant had flown to the United States, primarily to work with the Rad Lab on radar development -- but also to find out why reports on MAUD work sent to the USA seemed to disappear into a hole, with little comment being sent back over the Atlantic. When Oliphant called on Briggs, he found that "this inarticulate and unimpressive man had put the reports in a safe and had not shown them to members of his Committee." When Oliphant then met with the said committee, he found that its members had no clue about atomic bombs, one saying: "I thought we were making a power source for submarines."
Exasperated, Oliphant called Ernest Lawrence, and then flew to California at the beginning of September to meet with him. Oliphant told Lawrence about the final MAUD report, which Lawrence hadn't known about, and Lawrence told Oliphant about the progress of work at Berkeley on plutonium -- it was still generally referred to as "element 94" at the time, but the name plutonium is used here for convenience -- and other atomic research there. Oliphant wrote out a summary of the report for Lawrence, and Lawrence called Bush and Conant to arrange meetings with Oliphant.
Oliphant went back east to get a polite hearing from Conant, then a rushed chat with Bush, with neither giving him much encouragement. Even a chat with Fermi seemed unconstructive, with Fermi coming across as very non-committal. The Australian flew back to the UK wondering if he had accomplished anything at all.
* Actually, Oliphant had given the machinery just enough of a kick to get it moving. After Oliphant left California, Lawrence had called Arthur Compton in Chicago to say that the atomic bomb now seemed possible and that it might be the weapon to win the war. Compton was receptive, but he wasn't the person who had to be convinced. Lawrence was scheduled to give a speech in Chicago on 25 September, the same time that Conant would be town to accept an honorary degree. Compton set up a evening meeting at his house with the two men in hopes that Conant might be brought over to their point of view.
When the trio met that evening, Lawrence delivered an impassioned pitch to Conant, with Compton adding his weight on to Lawrence's persuasion. Conant started to turn around, but he still had to test Lawrence: "Ernest, you say you are convinced of the importance of these fission bombs. Are you ready to devote the next several years of your life to getting them made?"
Lawrence was startled -- obviously he hadn't thought out that issue -- but only hesitated for a moment before replying: "If you tell me this is my job, I'll do it."
It would be less accurate to say that Conant was convinced than that he was no longer opposed. He returned to Washington DC and discussed matters with Bush; the two then decided to revise the NAS committee once again to obtain a second report. The committee was expanded by the addition of W.K. Lewis, a chemical engineer with a legendary understanding of the implementation of lab processes on an industrial scale, and a Ukrainian expatriate named George Kistiakowsky, an NDRC chemist from Harvard.
A few weeks later Kistiakowsky told Conant: "It can be made to work. I am 100% sold." Conant accepted Kistiakowsky's judgement as definitive. Conant's conversion obviously influenced Bush, but in early October Bush also obtained the final copy of the MAUD report. It clinched the matter in Bush's mind: on 9 October 1941 he met with President Roosevelt and Vice-President Wallace. The message Bush carried was that atomic bombs were perfectly possible; it remained up to the president as to what to do about it.
Roosevelt regarded it as his decision and his decision alone. He saw, justifiably, the development of the atomic bomb as a military measure and so within his authority as Commander in Chief. What would become known as a "Top Policy" group would advise him on the matter, with the group consisting of Vice-President Wallace, Secretary of War Henry L. Stimson, Army Chief of Staff George C. Marshall, plus Bush and Conant. None of the scientists involved in atomic bomb research were included in the Top Policy group.
The conclusion of the meeting was that Bush was to expedite research but not move on to implementation until instructed by Roosevelt. The immediate problem was one of funding, which as Roosevelt said "would have to come from a special source available for such an unusual purpose ... " The president added: "I can arrange this." The wheels of government were finally starting to spin.
* In the meantime, Szilard and Fermi had been working on their first atomic pile. To have a sustained chain reaction, at least one neutron ejected from the fission of a uranium atom needed to cause the fission of another uranium atom. In more formal terms, as Fermi put it, the "reproduction factor k" had to be at least one.
Studies had shown that on average, uranium releases 2.5 neutrons per fission event, which put the maximum value of k as 2.5. Although that was much more than needed for a self-sustaining chain reaction, neutrons were invariably lost during the fission process, and so obtaining a chain reaction was not simple. Complicating the matter was the fact that nuclear processes occur very quickly, and even a reproduction factor slightly greater than one would cause a chain reaction increasing exponentially, cascading out of control in a hurry. There had to be some way of producing a chain reaction but keeping it under control.
Fortunately, research showed that a small fraction, less than a percent, of the neutrons emitted by the fission process were "delayed" neutrons. These delayed neutrons were emitted by the fission fragments after a certain time delay, instead of being emitted by the fission action itself. The time delay involved was surprisingly long, on the order of ten seconds. This means that if the value of k was between 1 and 1.01, the delayed neutrons decided the balance of the chain reaction, and the reaction was slow enough to be controlled.
A large room where the pile could be set up was found in one of Columbia's halls. The pile was built around cubic cans of uranium oxide, 20 centimeters (8 inches) on a side and surrounded with graphite to form cubic "cells" 40 centimeters (16 inches) on a side. There were 288 cans in the pile. It was hard work, and members of the Columbia's football team were hired on to haul the heavy cans of uranium oxide around. Fermi, always a trooper, tried to do his bit with the manual labor but he was outclassed. The first pile was completed in September 1941; it wasn't really expected to demonstrate a chain reaction, instead being seen as a demonstrator to help build a better pile that would be able to do the job. It would also help keep the funding coming in.
A radium-beryllium radioactive neutron source was placed at the bottom to try to promote fission. The neutron flux from the source fell off exponentially through the pile, and so the prototypes was known as an "exponential pile". Adding uranium reduced the slope of the exponential curve by increasing the neutron flux through fission. To perform measurements, strips of rhodium foil were inserted into slots in the graphite blocks. Rhodium becomes radioactive under neutron bombardment, allowing the neutron flux to be measured. The value of k obtained by the first pile was only 0.87 -- not good enough, but definitely a step in the right direction.
* The money wasn't flowing into atomic bomb development yet, but it would soon. Bush and Conant asked Arthur Compton to produce a third report under the umbrella of the NAS to nail down what needed to be done to build an atomic bomb. Compton's first stop was Columbia University in New York City, where he spoke with Fermi to find out how much fissionable material would be needed for a bomb. Fermi's estimate gave the worst-case amount as no more than 45 kilograms (100 pounds). It was an answer that Compton liked hearing.
There was then the big problem of figuring out how to obtain that fissionable material by isotope separation. While at Columbia, Compton also spoke to Columbia chemist Harold Clayton Urey, who had won the 1934 Nobel prize for isolating deuterium. Urey and several of his Columbia colleagues had been thinking over isotope separation for the previous few years, with Urey initially focusing on a centrifugal process -- converting uranium to a gas by combining it with some other element and then running the gas through a centrifuge, which would tend to separate the heavier uranium-238-based gas molecule from the uranium-235-based molecules. However, gaseous diffusion was beginning to seem more appealing. Urey was able to assure Compton that isotope separation would be feasible.
Compton then chatted with Eugene Wigner at Princeton, who pushed ideas Fermi had for producing plutonium and emphasized, almost in tears, that America needed to build an atomic bomb before the Nazis got there first. Finally, Compton spoke with Glenn Seaborg, who came out to Chicago from Berkeley for the meeting. Seaborg had ideas for separating plutonium from uranium and thought it perfectly practical.
* With all this information accumulated, Compton called a meeting of the various players in the NAS review effort, to take place on 21 October in Schenectady, New York. Lawrence brought along Robert Oppenheimer, a brilliant Berkeley physicist who Lawrence felt would be an asset to the effort. He would actually become central to it, but for the moment he was a newcomer.
Lawrence kicked off the meeting by reading off the notes Oliphant had given him concerning MAUD, with Compton adding a summary of what he had been told during his recent travels. Oppenheimer and Kistiakowsky added their optimistic views of the possibilities, but to Compton's frustration the engineers on the committee were unable to provide any suggestion as to how long development would take or how much it would cost. How could they? Nothing like it had ever been done before, there was absolutely no engineering data. Compton, unable to get an answer, asked them if it would be reasonable to say development might take from three to five years and cost hundreds of millions of dollars. They had no objection. The committee members then went their separate ways.
Compton now had answers to most of the basic questions about atomic bomb development, though some of them were a bit vague for comfort. There was one big question left unanswered, however: just how big of a bang would an atomic bomb make? Compton found locating help on the matter frustrating, but finally he obtained assistance from Oppenheimer, the two scientists having known each other for fourteen years. The third NAS report was released at the end of October 1941 and essentially summarized Compton's findings -- though the expected yield of an atomic bomb was speculatively offered as the equivalent of a few hundred tonnes of TNT. This would turn out to be thinking way too small.
* While the American atomic bomb development program began to accelerate, the war was not standing still. There had been concerns that Hitler would defeat the Soviets, but the German offensive into the USSR had bogged down as winter approached. On 5 December, the Red Army began a counterstroke that would send the Germans rolling back from the gates of Moscow.
Soviet dictator Josef Stalin had been able to stage the counterattack by pulling troops from the Siberian Far East. He could do this because he didn't fear a Japanese attack from that direction. Thanks to a spy in Japan, Stalin knew something that Roosevelt didn't: Japan was preparing to attack the United States, and wouldn't be able to make trouble for the USSR.
On the morning of 7 December 1941, the Imperial Japanese Navy attacked the US Navy base at Pearl Harbor, inflicting massive damage. The United States declared war on Japan. There was no mandate for America declaring war on Germany as well, but Hitler fixed that problem by declaring war on the USA on 11 December. America had expected to be at war sooner or later, but when it came, it hit like a thunderclap. The next six months would be news of one disaster after another.
* In Germany, Werner Heisenberg was conducting experiments that convinced him an atomic bomb was possible. At the end of October 1941, he attended a physics conference in occupied Copenhagen, and managed to swing a visit with his old mentor, Niels Bohr. The meeting did not go well. Bohr understood clearly enough that the Nazis seemed to be on the trail of the atomic bomb -- Heisenberg passed him a rough sketch of a nuclear pile using heavy water as a moderator -- and Bohr was shocked. He was all the more shocked because Heisenberg seemed to be asking for help, and Bohr was appalled at even the hint that he would collaborate with Nazi atomic bomb research. Heisenberg left feeling reproached and hurt, but though the meeting was a loss for him, it would actually end up adding force to the Allied atomic bomb effort.
* The US atomic bomb effort had already built up momentum before Pearl Harbor; the abrupt entry of the US into the war stepped up the pace. Arthur Compton, who was effectively in charge of the effort at that time, estimated that over the short term he would need over a million dollars -- what seemed like an astonishing sum of money to him at the time, since all the experiments he had conducted to that time had cost only thousands of dollars each.
Compton wanted to centralize atomic bomb research, leading to a debate among the players as to the best site -- Columbia, Princeton, Berkeley, the University of Chicago were among the candidates. Everybody lobbied for their own site, with few being willing to move, but in late January Compton, seeing no possibility of obtaining a consensus, simply declared the University of Chicago as the winner. The new organization was given the cover name of the "Metallurgical Laboratory" or just "Met Lab" for short.
Players like Fermi weren't happy at the move but understood the necessity. Before Fermi went west, he helped put together a second pile at Columbia. Szilard hadn't been able to obtain purer materials by that time, but the second pile featured a number of design improvements: the uranium oxide was no longer packed into cans, since their neutron absorption was too great, instead being pressed into cylindrical lumps about 7.5 centimeters in diameter and 7.5 centimeters tall (3 by 3 inches). About 2,000 were plugged into the new pile.
By the end of April 1942 a k of 0.913 had been measured. At the University of Chicago, physicist Samuel Allison had also put together a pile and measured an encouraging k of 0.94. In the meantime, Glenn Seaborg had finally left Berkeley to set up shop at Washington University in Saint Louis, heading a team working on plutonium separation.
* While Allied work on the atomic bomb built up steam, German efforts towards that end drifted. The Soviet counteroffensive of December 1941 faded out in a few months, but the Wehrmacht was badly pressed for a time, and the result was that resources had to be diverted from research programs towards supporting the immediate war effort. The Nazi atomic bomb effort was hit by funding cutbacks. The physicists tried to lobby for more money, but a presentation by Heisenberg and others to senior Nazi officials on the importance of atomic bomb research fell flat: due to a paperwork mixup, attendance was sparse, and though Heisenberg spoke of the possibilities of nuclear power and atomic bombs, there was no one there to listen.
The really key figure to convince was Albert Speer, Nazi Minister of Armaments and War Production. He didn't attend the February meeting and didn't get word of the notion of the atomic bomb until spring. He discussed the matter with the Fuehrer and attended a second presentation on 4 June 1942, in which Heisenberg again spoke of nuclear power and the atomic bomb. However, this did not result in German atomic bomb research shifting into high gear; in fact, it had almost the opposite effect.
Although Speer had further discussions with Hitler on the matter, the Fuehrer didn't take the idea very seriously, and when the physicists then told Speer that it might take three or four more years to build an atomic bomb, the only conclusion was that it wasn't worth the bother over the short run. Hitler remained confident of winning the war quickly, and the conflict would be over by the time a German bomb might be available. There was no reason to rush. Hitler also had misgivings about such a powerful weapon: he wanted to dominate the world, not blow it up.
The Germans gave up on the development of the atomic bomb, even as fears of what the Nazis were up to pushed Allied work into high gear. Research continued on the use of nuclear power to propel submarines and other naval vessels, with the focus on development of a nuclear pile using heavy water as the moderator.
* By late June 1942, the OSRD and the US Army Corps of Engineers were beginning to consider the groundwork for a full-scale atomic bomb project. Civilian contractors were tapped to build production facilities. On 27 June, Compton conducted a meeting of Met Lab research personnel in Chicago -- including Fermi, Seaborg, Szilard, Teller, Wigner, and others in attendance -- to inform them of developments. Not everybody in the audience was entirely happy with the situation as reported, since the scientists were now being confronted with the idea of having to submit to an industrial, or worse a military, organization. Szilard in particular raised objections.
The work went ahead regardless. Seaborg's group continued to work on isotope separation, while Fermi and Szilard worked on improved piles. Szilard's persistent efforts in obtaining purer graphite, uranium oxide, and uranium metal began to pay off, with a test run in July obtaining a value of k = 1.004 and another in August giving a value of k = 1.014.
In the meantime, Robert Oppenheimer was assembling a study group at the University of California, Berkeley, to lay the theoretical groundwork for building an atomic bomb. Hans Bethe and Edward Teller were in attendance; by this time, Teller had reconsidered his rejection of the fusion bomb, and ideas were also floated for how to build the "Super Bomb". By the end of summer, a report was produced that went upstairs to Vannevar Bush. The report said that an atomic bomb could be available as early as March 1944, and that it could have a yield of up to 100,000 tons of TNT. The paper also suggested that a "Super" bomb could be a hundred times more powerful. The days of equivocation about the bomb program were now completely over. On 17 September, the Army assigned Colonel Leslie Groves to take charge of the atomic bomb project.
Groves was a big, beefy, man who suggested a bulldozer, with a streak of overbearing arrogance a mile wide. Most who worked for or with him disliked him, but they also respected him, because he was boundlessly energetic, highly decisive, and extremely competent. He had been working as chief of operations for General Brehon Somervell on construction of the Pentagon building. Now that the Pentagon project was winding down, was looking for a combat command and the prestige that came with it. Being told he had to remain stateside and work on engineering projects was a big let-down.
When Somervell told Groves: "If you do the job right, it will win the war." -- Groves replied: "Oh." Groves was promoted to brigadier general to give him the necessary authority, which took some of the sting out of an unwanted duty assignment. The effort had already been given the cover name of the "Manhattan Engineering District", which to any snoops would probably suggest a water or harbor project for New York City. It would become more informally known as the "Manhattan Project".
Groves appeared before a group of senior officials in Secretary of War Stimson's office on 23 September, the day his promotion became official. Bush, Conant, Somervell, and Army Chief of Staff George Marshall were among the attendees, and Groves' take-charge no-nonsense attitude made an excellent impression. When Stimson suggested a nine-man oversight committee, Groves talked him down to a committee of three, and when the meeting finally slowed down, Groves asked to be excused to take a train to Tennessee, where he was to inspect a site being lined up for the project. Somervell told him later: "You made me look like a million dollars."
* Between 15 September and 15 November 1942, the Met Lab built at least 16 exponential piles and performed hundreds of tests. At the end of this cycle, the group was obtaining values of k = 1.04 with uranium oxide and k = 1.07 with uranium metal. The work demonstrated that a practical pile capable of supporting a controlled fission reaction could be built with the materials at hand, and it could be operated safely. Work began on the full-scale pile, unimaginatively named "Chicago Pile One", on 16 November 1942.
Pile One was assembled in a squash court under the west grandstand of the University of Chicago's football stadium. The pile was to be about 7.6 meters (25 feet) wide and 6.1 meters (20 feet) high. It would contain 360 tonnes (400 tons) of graphite, 36 tonnes (40 tons) of uranium oxide, and 5.4 tonnes (6 tons) of uranium metal, provided by a group at the University of Iowa that was learning to produce the metal in bulk quantities. Nobody knew how far the Germans were along in their efforts to develop a Nazi bomb, so work went on around the clock in two 12-hour shifts. The day shift was run by Walter Zinn and the night shift by Herbert Anderson, colleagues of Fermi's from his Columbia days.
The graphite came in long blocks and had to be sawed, ground down, and drilled with holes, making the work extremely dirty. The uranium oxide was pressed with a hand tool into 22,000 egg-shaped slugs. The graphite bricks were laid down meticulously inside a wood scaffold, with the uranium oxide slugs inserted in one layer of bricks, followed by a layer of pure graphite, then another layer of bricks with slugs. Channels were cut into the pile to allow the insertion of cadmium control rods, which would strongly absorb neutrons and damp a chain reaction until removed. Fermi worked as an administrator, tracking the construction of the pile on a daily basis. With his accustomed meticulousness, he had careful measurements of the neutron flux from the pile performed at the end of every shift.
The 52nd layer was laid down on 30 November. Fermi's calculations based on the measurements taken indicated the pile would reach k = 1 when the 57th layer was laid down. On the frigid morning of 2 December 1942, Pile One was ready to conduct the first controlled fission experiment in history. Nobody thought the pile was capable of exploding, but there were worries that if the chain reaction got out of control, the pile might break down and scatter radioactive debris over the campus. Compton had not informed the president of the University of Chicago of what exactly was going on, knowing that the university administration would have refused to permit it.
Fermi believed the risk was small and approached the operation with his typical care, directing his team through careful procedures every step of the way. The cadmium control rods were pulled out of the pile, until there was only one left, under the control of George Weil. There was an automatic safety rod that would be plunged into the pile if the chain reaction started to get out of control, plus another that was held in place by a rope that would be cut by a man with an axe. Three men stood over the pile with buckets of a cadmium-salt solution to douse the pile as a last-ditch defense.
The final control rod was pulled out by stages, with measurements at each stage. The neutron flux increased until an automatic safety rod slammed into place. Fermi shut down the pile and broke the session for lunch. After lunch, they resumed the procedures. At 3:42 PM, Weil pulled the final control rod out, and the neutron flux rose in a slow and controlled fashion. Fermi checked his figures with a slide rule, smiled, and said: "The reaction is self sustaining." They ran the pile for 11 minutes and then shut it down. The group broke out a bottle of Chianti that Wigner had brought in, and drank it with paper cups. Pile One was working as expected, providing the physicists with an easily controlled fission source. Its power output was only half a watt, but it was a superb research tool for bigger and better things.
Compton went back to his office and called Conant in Washington: "Jim, you'll be interested to know that the Italian navigator has just landed in the New World. The Earth was not as large as he had estimated, and he arrived at the New World sooner than he had expected."
Conant was excited: "Izzat so? Were the natives friendly?"
"Everyone landed safe and happy." Not everyone was happy, however. Leo Szilard went up to Fermi afterwards and shook his hand, saying: "This day will go down as a black day in the history of mankind."
* Les Groves wasn't unhappy with the news about Pile One at all, and in fact he was probing around for a site where bomb development could be put into high gear. He was also looking around for a scientist to become technical head of the project. Partly due to the lack of anyone else, he settled on Robert Oppenheimer.
There were certainly valid reasons for selecting Oppenheimer. A son of a wealthy family of secular Jews, "Oppie", as his friends knew him, was noted for his extreme brilliance and ability to grasp difficult concepts quickly. He tended to be impatient and sloppy with details, but had learned to delegate the "grunt work" to his grad students, many of whom were dedicated to him. He was energetic and could be extremely charismatic.
That, however, was the "good" Robert Oppenheimer. There was also the "bad" Robert Oppenheimer -- a pretentious intellectual with his own streak of arrogance and little patience with inferior intellects, resulting in a nasty habit to make lifelong enemies without good reason. He was smart enough to realize he could be "beastly" and tried to restrain it, though with spotty success. He also a bad diet, poor teeth, liked to drink martinis a bit too much and the details of his sex life didn't bear too much investigation. Worse, from the Army's point of view, he had a background of flirtations with Communism. He'd never been a party member and interviews with Army intelligence folks demonstrated he wasn't a security risk -- though it would turn out later he wasn't completely truthful with the Army men.
There was something tragically confused about Robert Oppenheimer. Physicist Isaac Isidore ("I.I.") Rabi -- a manager at the MIT Rad Lab who would work with the atomic bomb project as a consultant on occasions -- once said of Oppie that he couldn't make up his mind as to whether he wanted to lead the Knights of Columbus parade or head the local chapter of the B'nai B'rith. Oppenheimer flitted around with too many ideas, dabbling in this and that, and those who knew him were frustrated to see a man who they saw as potentially one of the world's great physicists, an American Einstein, unable to really live up to his potential as a scientist.
Oppenheimer's confusions would catch up with him eventually, but war and responsibility brought the good Oppie to the front. Even those scientists who had misgivings about him initially, many thinking that the project technical leader necessarily had to be a Nobelist, would eventually say that Groves had made a brilliant choice. Oppenheimer would demonstrate outstanding leadership capability, proving decisive and balanced while able to hold all the necessary technical details in his head. If he wouldn't go down in history as one of the greatest physicists, he would achieve fame in his own way.
* Groves' staff had put together a list of potential atomic bomb development sites in the US West. When Oppenheimer visited some of the sites in the New Mexico desert regions in mid-November, he fell in love with the scenery at a mesa site, inhabited only by the Los Alamos boy's school. It wasn't technically the best site, but Oppenheimer liked the deserts -- and if it made Oppenheimer happy, Groves felt that was good enough. The land was purchased before the month was out. Groves arranged for the University of California to operate the installation. Construction of barracks and other facilities began immediately; the general was wasting absolutely no time. Oppenheimer began to recruit researchers to the cause, directing people who had signed up to get their hands on the needed equipment.
The recruiting effort quickly ran into a big snag: military security. Groves wanted to draft all the physicists into the Army as officers. They were not as a rule keen on this idea, or in fact on the idea of a security regime in general. Most understood the necessity of it, but felt that it would be impossible to build the atomic bomb if everything was compartmentalized and security snoops were around in swarms. Oppenheimer managed to persuade Groves to relent on drafting the physicists, and arranged for the lab to operate in an open fashion -- internally. It wasn't open to the outside world, being contained by a double barbed-wire fence and security checkpoints. Some of the staff who had fled Europe found it unpleasantly reminiscent of a concentration camp, but it was what had to be done.
Oppenheimer arrived in Santa Fe, New Mexico, in mid-March 1943 with a group of his aides. By the first of April, about thirty researchers of the hundred initial hires were present; the Los Alamos facility was still being thrown together, so Groves had commandeered isolated local guest ranches to house the them. Oppenheimer set up "orientation" sessions, with his student Robert Serber telling the research crew about such progress as had been made on building the atomic bomb to that time. Serber provided sketches of a number of different bomb configurations, the two most significant in hindsight being the "gun" type configuration, in which a slug of fissionable material was shot into a "core" with a matching hole to reach an explosive critical mass; and an "implosion" type configuration, in which wedges of fissionable material were blasted together to form a sphere with a critical mass.
By the end of April 1943, the operation was fully staffed and Los Alamos was a going concern. Many of the researchers didn't like the barbed wire, but were willing to put up with it -- there was a war on, after all. There was also grumbling about delays and Army "hurry up and wait", but not because of the inconvenience. Every day added to the delay in building the atomic bomb and putting an end to the war meant that more people would die.