Manhattan Project

This article is about the atomic bomb project. For other uses, see Manhattan Project (disambiguation).

Manhattan Engineer District (MED)
The Manhattan Project created the first nuclear bombs. The first human-engineered nuclear detonation, the Trinity test, is shown.
Active	1942–1946
Disbanded	31 December 1946
Country	United States United Kingdom Canada
Branch	United States Army Corps of Engineers
Garrison/HQ	Oak Ridge, Tennessee
Anniversaries	13 August 1942
Engagements	Allied Invasion of Italy Allied Invasion of France Allied Invasion of Germany Atomic bombings of Hiroshima and Nagasaki Allied Occupation of Japan
Commanders
Notable commanders	Leslie R. Groves Kenneth D. Nichols
Insignia
Shoulder patch of the Manhattan Engineer District, which was adopted in 1945

The Manhattan Project was the effort, led by the United States with participation from the United Kingdom and Canada, which led to the development of the first atomic bomb during World War II. From 1942 to 1946 the project was under the command of Major General Leslie R. Groves Jr. of the US Army Corps of Engineers. The Army component of the project was designated the Manhattan District or Manhattan Engineer District, but "Manhattan" gradually superseded the official codename for the project.

The project had its roots in the Einstein–Szilárd letter, which warned that Nazi Germany might develop nuclear weapons. The letter was written by prominent physicists, signed by Albert Einstein, and delivered to President Franklin D. Roosevelt in October 1939. The Manhattan Project, which began as a small research program that year, eventually employed more than 130,000 people at a cost of nearly US$2 billion. Research and production took place at more than 30 sites, some secret, including universities across the United States, Canada, and the United Kingdom. The three primary research and production sites of the project were the plutonium-production facility at the Hanford Site in eastern Washington state, the uranium enrichment facilities at Oak Ridge, Tennessee, and the weapons research and design laboratory at Los Alamos, New Mexico.

Little Boy, the bomb that was eventually dropped at Hiroshima, was a gun-type fission weapon made from uranium-235, an isotope of uranium that makes up only 0.7% of natural uranium. This isotope proved difficult to separate from the main isotope, uranium-238, since it was chemically identical and almost the same weight. Three methods were employed for uranium enrichment, and most of the work was performed at Oak Ridge. Fat Man, the more complex plutonium-core bomb dropped at Nagasaki, was an implosion-type nuclear weapon that required a concerted design and construction effort from Los Alamos. A plutonium bomb was the first nuclear device ever detonated, at the Trinity test in July 1945.

The Manhattan Project was also charged with gathering intelligence on the German nuclear energy project. Through Operation Alsos, it gathered nuclear materials and rounded up German scientists. The MED maintained control over American atomic weapons production until the formation of the United States Atomic Energy Commission in January 1947.

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Feasibility

A 1940 meeting at Berkeley with (from left to right) Ernest O. Lawrence, Arthur H. Compton, Vannevar Bush, James B. Conant, Karl T. Compton and Alfred L. Loomis

Proposals

The S-1 Committee held its first meeting on 18 December "pervaded by an atmosphere of enthusiasm and urgency" in the wake of the attack on Pearl Harbor and the subsequent declaration of war by the United States on Germany and Japan. Work was proceeding on three different techniques for isotope separation to separate uranium-235 from uranium-238. Lawrence and his team at the University of California, Berkeley investigated electromagnetic separation, while Eger Murphree and Jesse Wakefield Beams' team looked into gaseous diffusion at the University of Columbia, and Philip Abelson directed research into liquid thermal diffusion at the Carnegie Institution of Washington and later the Naval Research Laboratory. Murphree was also the head of the centrifruge project.

Meanwhile, there were two lines of research into reactor technology, with Harold Urey continuing research into heavy water at Columbia, while Arthur Compton brought the scientists working under his supervision at Columbia University and Princeton University to the University of Chicago, where he organized the University of Chicago Metallurgical Laboratory in early 1942 to study plutonium and nuclear reactors using nuclear graphite as a neutron moderator. Briggs, Compton, Lawrence, Murphree and Urey met on 23 May to finalize the S-1 Committee recommendations, which called for all five technologies to be pursued. This was approved by Bush, Conant and Brigadier General Wilhelm D. Styer, the chief of staff of Major General Brehon B. Somervell's Services of Supply, who had been designated the Army's representative. They took the recommendation to the Top Policy Group with a budget proposal for $54 million for construction by the United States Army Corps of Engineers, $31 million for research and development by OSRD and $5 million for contingencies in fiscal year 1943. The Top Policy Group sent it to the President on 17 June 1942 and he approved it by writing "OK FDR" on the document.

Bomb design concepts

Compton asked the theoretical physicist J. Robert Oppenheimer of the University of California, Berkeley to take over research into fast neutron calculations—the key to calculations of critical mass and weapon detonation—from Gregory Breit, who had quit on 18 May 1942 because of concerns over lax operational security. John H. Manley, a physicist at the Metallurgical Laboratory, was assigned to assist Oppenheimer by contacting and coordinating experimental physics groups scattered across the country. Oppenheimer and Robert Serber of the University of Illinois examined the problems of neutron diffusion—how neutrons moved in a nuclear chain reaction—and hydrodynamics—how the explosion produced by a chain reaction might behave. To review this work and the general theory of fission reactions, Oppenheimer convened meetings at the University of Chicago in June and at the University of California, Berkeley, in July 1942 with theoretical physicists Hans Bethe, John Van Vleck, Edward Teller, Emil Konopinski, Robert Serber, Stan Frankel, and Eldred C. Nelson, the latter three former students of Oppenheimer, and experimental physicists Felix Bloch, Emilio Segrè, John Manley and Edwin McMillan. They tentatively confirmed that a fission bomb was theoretically possible.

Different fission bomb assembly methods explored during the July 1942 conference

There were still many unknown factors. The properties of pure uranium-235 were relatively unknown, as were those of plutonium, a new element which had only been discovered in February 1941 by Glenn Seaborg and his team. The scientists at the Berkeley conference envisioned creating plutonium in nuclear reactors where uranium-238 atoms absorbed neutrons which had been emitted from fissioning uranium-235 atoms. At this point no reactor had been built, and only tiny quantities of plutonium were available from cyclotrons. Even by December 1943, only two milligrams had been produced. There were many ways of arranging the fissile material into a critical mass. The simplest was shooting a "cylindrical plug" into a sphere of "active material" with a "tamper"—dense material that would focus neutrons inward and keep the reacting mass together to increase its efficiency. They also explored designs involving spheroids, a primitive form of "implosion" suggested by Richard C. Tolman, and the possibility of autocatalytic methods, which would increase the efficiency of the bomb as it exploded.

Considering the idea of the fission bomb theoretically settled—at least until more experimental data was available—the Berkeley conference then turned in a different direction. Edward Teller pushed for discussion of a more powerful bomb: the "super", now usually referred to as a "hydrogen bomb", which would use the explosive force of a detonating fission bomb to ignite a nuclear fusion reaction in deuterium and tritium. Teller proposed scheme after scheme, but Bethe refused each one. The fusion idea was put aside to concentrate on producing fission bombs. Teller also raised the speculative possibility that an atomic bomb might "ignite" the atmosphere because of a hypothetical fusion reaction of nitrogen nuclei. Bethe calculated that it could not happen, and a report co-authored by Teller showed that "no self-propagating chain of nuclear reactions is likely to be started." In Serber's account, Oppenheimer mentioned it to Arthur Compton, who "didn't have enough sense to shut up about it. It somehow got into a document that went to Washington" which led to the question being "never laid to rest".

Organization

Manhattan Engineer District

The Chief of Engineers, Major General Eugene Reybold selected Colonel James C. Marshall to head the Army's part of the project in June 1942. Marshall created a liaison office in Washington, D.C. but established his temporary headquarters on the 18th floor of 270 Broadway in New York City, where he could draw on administrative support from the Corps of Engineers' North Atlantic Division. It was close to the Manhattan office of Stone & Webster, the principal project contractor, and to Columbia University. He had permission to draw on his former command, the Syracuse District, for staff, and he started with Lieutenant Colonel Kenneth D. Nichols, who became his deputy.

Because most of his task involved construction, Marshall worked in cooperation with the head of the Corps of Engineers Construction Division, Major General Thomas M. Robbins and his deputy, Colonel Leslie R. Groves, Jr. Reybold, Somervell and Styer decided to call the project "Development of Substitute Materials", but Groves felt that this would draw attention. Since engineer districts normally carried the name of the city where they were located, Marshall and Groves agreed to instead name it the Manhattan District. This became official on 13 August, when Reybold issued the order creating the new district. Unlike other districts, it had no geographic boundaries, and Marshall had the authority of a division engineer. "Development of Substitute Materials" remained as the project codename, but was supplanted over time by "Manhattan".

Marshall later conceded that "I had never never heard of atomic fission but I did know that you could not build much of a plant, much less four of them for $90 million." A single TNT plant that Nichols had recently built in Pennsylvania had cost $128 million. Nor were they impressed with estimates to the nearest order of magnitude, which Groves compared with telling a caterer to prepare for between ten and a thousand guests. A survey team from Stone & Webster had already scouted a site for the production plants. The War Production Board recommended sites in the Knoxville, Tennessee area, an isolated area where the Tennessee Valley Authority could supply ample electric power and the rivers could provide cooling water for the reactors. After examining several sites, the survey team selected one at Oak Ridge, Tennessee. Conant advised that it be acquired at once and Styer agreed but Marshall temporized, awaiting the results of Conant's reactor experiments before taking action. Of the prospective processes, only Lawrence's electromagnetic separation appeared sufficiently advanced for construction to commence.

Marshall and Nichols began assembling the resources they would need. The first step was to obtain a high priority rating for the project. The top ratings were AA-1 through AA-4 in descending order, although there was also a special AAA rating reserved for emergencies. Ratings AA-1 and AA-2 were for essential weapons and equipment, so Colonel Lucius D. Clay, the deputy chief of staff at Services and Supply for requirements and resources, felt that the highest rating he could assign was AA-3, although he was willing to provide a AAA rating on request for critical materials if the need arose. Nichols and Marshall were disappointed; AA-3 was the same priority as Nichols' TNT plant in Pennsylvania.

Military Policy Committee

J. Robert Oppenheimer and Leslie Groves at remains of the Trinity test in September 1945. The white overshoes prevent fallout from sticking to the soles of their shoes.

Bush became dissatisfied with Colonel Marshall's failure to get the project moving forward expeditiously, specifically the failure to acquire the Tennessee site, the low priority allocated to the project by the Army, and the location of his headquarters in New York City. Bush felt that more aggressive leadership was required, and spoke to Harvey Bundyand Generals Marshall, Somervell and Styer about his concerns. He wanted the project placed under a senior policy committee, with a prestigious officer, preferably Styer, as overall director.

Somervell and Styer selected Groves for the post, informing him on 17 September of this decision, and that General Marshall ordered that he be promoted to brigadier general, as it was felt that the title "general" would hold more sway with the academic scientists working on the Manhattan Project. Groves' orders placed him directly under Somervell rather than Reybold, with Colonel Marshall now answerable to Groves. Groves established his headquarters in Washington, D.C. on the fifth floor of the New War Department Building in Washington, D.C., where Colonel Marshall had his liaison office. He assumed command of the Manhattan Project on 23 September. Later that day, he attended a meeting called by Stimson which established a Military Policy Committee, responsible to the Top Policy Group, consisting of Bush, with Conant as an alternate, Styer and Rear Admiral William R. Purnell. Tolman and Conant were later appointed as Groves' scientific advisers.

On 19 September Groves went to Donald Nelson, the chairman of the War Production Board and asked for broad authority to issue a AAA rating whenever it was required. Nelson initially balked but quickly caved in when Groves threatened to go to the President. Groves promised not to use the AAA rating unless it was necessary. It soon transpired that for the routine requirements of the project the AAA rating was too high but the AA-3 rating was too low. After a long campaign, Groves finally received AA-1 authority on 1 July 1944.

One of Groves' early problems was to find a director for Project Y, the group that would design and build the bomb. The obvious choice was one of the three laboratory heads, Urey, Lawrence and Compton, but they could not be spared. Compton recommended Oppenheimer, but he had two drawbacks. Unlike those three, Oppenheimer had not won a Nobel Prize and many scientists felt that the head of such an important laboratory should have one. There were also concerns about his security status, as many of Oppenheimer's associates were communists, including his brother Frank Oppenheimer, his wife Kitty and his girlfriend Jean Tatlock. A long conversation on a train in October 1942 convinced Groves and Nichols that Oppenheimer thoroughly understood the issues involved in setting up a laboratory in a remote area and should be appointed as its director. Groves personally waived the security requirements and issued Oppenheimer a clearance on 20 July 1943.

Collaboration with Britain

The British and Americans exchanged nuclear information but did not initially pool their efforts. The British rebuffed efforts by Bush and Conant in 1941 to strengthen cooperation with the British project, code-named Tube Alloys. However, Britain did not have the manpower or resources of the United States, and despite its early and promising start, the British project soon fell behind its American counterpart. On 30 July 1942, Sir John Anderson, the minister responsible for Tube Alloys, advised Churchill that: "We must face the fact that... [our] pioneering work... is a dwindling asset and that, unless we capitalize it quickly, we shall be outstripped. We now have a real contribution to make to a 'merger.' Soon we shall have little or none." By this time, the British bargaining position had worsened, and their motives were mistrusted by the Americans. Collaboration therefore lessened markedly, and the exchange of information stopped.

In August 1943 Churchill and Roosevelt negotiated the Quebec Agreement, which resulted in a resumption of cooperation. The subsequent Hyde Park Agreement in September 1944 extended this cooperation to the post-war period. The Quebec Agreement established the Combined Policy Committee to coordinate the efforts of the United States, Britain and Canada. Stimson, Bush and Conant served as the American members of the Combined Policy Committee; Field Marshal Sir John Dill and Colonel J. J. Llewellin were the British members; and C. D. Howe was the Canadian member. Llewellin returned to the United Kingdom at the end of 1943 and was replaced on the committee by Sir Ronald Ian Campbell, who in turn was replaced by the British Ambassador to the United States, Lord Halifax, in early 1945. Sir John Dill died in Washington, D.C. in November 1944 and was replaced both as Chief of the British Joint Staff Mission and as a member of the Combined Policy Committee by Field Marshal Sir Henry Maitland Wilson.

James Chadwick pressed for British involvement in the Manhattan Project to the fullest extent. With Churchill's backing, he attempted to ensure that every request from Groves for assistance was honored. The British Mission that arrived in the United States in December 1943 included Niels Bohr, Otto Frisch, Klaus Fuchs, Rudolf Peierls and Ernest Titterton. Part of Quebec Agreement specified that nuclear weapons would not be used against another country without mutual consent. In June 1945 Wilson agreed that the use of nuclear weapons against Japan would be recorded as a decision of the Combined Policy Committee.

The Combined Policy Committee created the Combined Development Trust in June 1944, with Groves as its chairman, to procure uranium and thorium ores on international markets. In 1944, the Combined Development Trust purchased 3,440,000 pounds (1,560,000 kg) of uranium oxide ore from companies operating mines in the Belgian Congo. In order to avoid briefing US Secretary of the Treasury Henry Morgenthau Jr. on the project, a special account not subject to the usual auditing and controls was used to hold Trust monies. Between 1944 and the time he resigned from the Trust in 1947, Groves deposited a total of $37.5 million into the Trust's account.

Project sites

A selection of U.S. sites important to the Manhattan Project. Click on the location for more information.

Oak Ridge

The day after he took over the project, Groves and Colonel Marshall took a train to Tennessee to inspect the site for the Clinton Engineer Works (CEW), the proposed production plant at Oak Ridge. Groves was suitably impressed. On 29 September, United States Under Secretary of War Robert P. Patterson authorized the Corps of Engineers to compulsorily acquire 56,000 acres (23,000 ha) of land at a cost of $3.5 million. An addition 3,000 acres (1,200 ha) was subsequently acquired. About 1,000 families were affected by the condemnation order which came into effect on 7 October. Protests, legal appeals, and a 1943 congressional inquiry were to no avail. By mid-November US Marshals were tacking notices to vacate on farmhouse doors, and construction contractors were moving in. Some families were given two weeks' notice to vacate family farms that had been their homes for generations; others had settled there after being evicted to make way for the Great Smoky Mountains National Park in the 1920s or the Norris Dam in the 1930s. The ultimate cost of land acquisition in the area, which was not completed until March 1945, was only about $2.6 million, which worked out to around $47 an acre. When presented with Public Proclamation Number Two, which declared Oak Ridge a total exclusion zone, the Governor of Tennessee, Prentice Cooper, angrily tore it up.

The population of Oak Ridge peaked at 75,000 in May 1945, at which time 82,000 people were employed at the Clinton Engineer Works. The Army presence at Oak Ridge increased in August 1943 when Nichols replaced Marshall as head of the Manhattan Engineer District. One of his first tasks was to move the district headquarters to Oak Ridge although the name of the district did not change. In September 1943 the administration of community facilities was outsourced to Turner Construction Company through a subsidiary known as the Roane-Anderson Company after Anderson and Roane counties, in which Oak Ridge was located. By 1945 it employed some 10,000 people.

Los Alamos

The idea of locating Project Y at Oak Ridge was considered, but in the end it was decided to locate it in a remote, isolated location. On Oppenheimer's recommendation, the search for a suitable site was narrowed to the vicinity of Albuquerque, New Mexico, where Oppenheimer owned a ranch. In October 1942, Major John H. Dudley of the Manhattan Project was sent to survey the area, and he recommended a site near Jemez Springs, New Mexico. On 16 November, Oppenheimer, Groves, Dudley and others toured the site. Oppenheimer feared that the high cliffs surrounding the site would make his people feel claustrophobic, while the engineers were concerned with the possibility of flooding. The party then moved on to the vicinity of the Los Alamos Ranch School. Oppenheimer was impressed and expressed a strong preference for the site. The engineers were concerned about the poor access road and the water supply, but otherwise felt that it was ideal.

Patterson approved the acquisition of the site on 25 November 1942, authorizing $440,000 for the purchase of the 54,000-acre (22,000 ha) site, all but 8,900 acres (3,600 ha) of which were already owned by the Federal Government. Secretary of Agriculture Claude R. Wickard authorized the War Department's use of some 46,000 acres (19,000 ha) of United States Forest Service land "so long as the military necessity continues". The need for land for a new road, and later for a right of way for a 25 miles (40 km) power line, eventually brought wartime land purchases to 45,737 acres (18,509 ha), but only $414,971 was spent. Construction was contracted to the M. M. Sundt Company of Tucson, Arizona, with Willard C. Kruger and Associates of Santa Fe, New Mexico as architect and engineer. Work commenced in December 1942. Groves initially allocated $300,000 for construction, three times Oppenheimer's estimate, with an estimated completion date of 15 March 1943. It soon became clear that the scope of Project Y was greater than expected, and by the time Sundt finished in 30 November 1943, over $7 million had been spent.

Because it was secret, Los Alamos was referred to as "Site Y" or "the Hill". Birth certificates of babies born in Los Alamos during the war had their place of birth listed as PO Box 1663 in Santa Fe. Initially Los Alamos was to be a military laboratory with Oppenheimer and other researchers commissioned into the Army. Oppenheimer went so far as to order himself a lieutenant colonel's uniform, but two key physicists, Robert Bacher and Isidor Rabi baulked at the idea. As a result, Conant, Groves and Oppenheimer devised a compromise whereby the laboratory was operated by the University of California under contract to the War Department.

Argonne

Shift change at the Y-12 uranium enrichment facility at Oak Ridge.

An Army-OSRD meeting on 25 June 1942 decided to build a pilot plutonium plant in the Argonne Forest southwest of Chicago. In July, Nichols arranged for a lease of 1,000 acres (400 ha) from Cook County, Illinois and Captain James F. Grafton was appointed Chicago area engineer. It soon became apparent that the scale of operations was too great for the Argonne, and plans were redrawn to locate the pilot plant at Oak Ridge.

Delays in establishing Argonne led Compton to authorize construction of the first nuclear reactor beneath the bleachers of Stagg Field at the University of Chicago. On 2 December 1942 a team led by Enrico Fermi, initiated the first artificial self-sustaining nuclear chain reaction in an experimental reactor known as Chicago Pile-1. The point at which a reaction becomes self-sustaining became known as "going critical". Compton reported the success to Conant in Washington, D.C. by a coded phone call, saying, "The Italian navigator [Fermi] has just landed in the new world." In January 1943, Grafton's successor, Major Arthur V. Peterson, ordered Chicago Pile-1 dismantled and reassembled at Argonne, as he regarded the operation of a reactor as too potentially hazardous for a densely populated area.

Hanford

By December 1942 there were concerns that even Oak Ridge was too close to Knoxville, Tennessee in the unlikely but possible event of a major nuclear accident. Groves recruited DuPont in November 1942 to be the prime contractor for the construction of the plutonium production complex. DuPont was offered a standard cost-plus fixed fee contract, but the President of the company, Walter S. Carpenter, Jr., wanted no fee or profit of any kind, and asked for the proposed contract to be amended to explicitly exclude the company from acquiring any patent rights. This was accepted, but for legal reasons a nominal profit of one dollar was agreed upon. After the war, DuPont asked to be released from the contract early, and had to return 33 cents.

Reactor B under construction at the Hanford site

DuPont recommended that the site be located far from the existing uranium production facility at Oak Ridge. In December 1942, Groves dispatched Colonel Franklin Matthias and DuPont engineers to scout potential sites. Matthias reported that Hanford Site near Richland, Washington was "ideal in virtually all respects". It was isolated and near the Columbia River, which could supply sufficient water to cool the reactors which would produce the plutonium. Groves visited the site in January and established the Hanford Engineer Works (HEW), codenamed "Site W". Under Secretary Patterson gave his approval on 9 February, allocating $5 million for the acquisition of 40,000 acres (16,000 ha) of land in the area. The federal government relocated some 1,500 residents of White Bluffs and Hanford, and nearby settlements, as well as the Wanapum and other tribes using the area. A dispute arose with farmers over the issue of crops which had already been planted before the land was acquired, for which the farmers expected compensation. Where schedules allowed, the Army allowed the crops to be harvested, but this was not always possible. The land acquisition process dragged on and was not completed before the end of the Manhattan Project in December 1946.

This did not delay work. Although progress on the reactor design at Metallurgical Laboratory and DuPont was not sufficiently advanced to accurately predict the scope of the project, a start was made in April 1943 on facilities for an estimated 25,000 workers, half of whom were expected to live on site. By July 1944, some 1,200 buildings had been erected and nearly 51,000 people were living in the construction camp. As area engineer, Matthias exercised overall control of the site. At its peak, the construction camp was the third most populous town in Washington state. Hanford operated a fleet of over 900 buses, more than the city of Chicago. Like Los Alamos and Oak Ridge, Richland was a gated community, with restricted access. However it looked outwardly more like a typical wartime American boomtown, because the military profile was lower, and physical security elements like high fences and guard dogs were less evident.

Canadian sites

Cominco had produced electrolytic hydrogen at Trail, British Columbia since 1930. Urey suggested in 1941 that it could produce heavy water. To the existing $10M plant consisting of 3,215 cells consuming 75 MW of hydro-electric power was added secondary electrolysis cells to increase the deuterium concentration in the water from the exchange process from 2.3% to 99.8%. For this process, Hugh Taylor of Princeton developed a platinum on carbon catalyst for the first three stages while Urey developed a nickel-chromia one for the fourth stage tower. The final cost was $2.8 million. The Canadian Government did not officially learn of the project until August 1942. Trail heavy water production started in January 1944 and continued until 1956. Heavy water from Trail was used for the Argonne reactor—the first heavy water/natural uranium reactor—which went critical on 15 May 1944.

The Chalk River, Ontario site was established to house the Allied effort that was going on at McGill University at the Montreal Laboratory. Since the site was 120 miles (190 km) west of Ottawa, a new community was built at Deep River, Ontario to provide residences and facilities for the team members. The site was chosen for its proximity to the industrial manufacturing of Ontario and Quebec, and access to a rail head adjacent to a large military base, Camp Petawawa. Located on the Ottawa River it had access to abundant water. The first director of the new laboratory was John Cockroft, but he was later replaced by Bennett Lewis. A pilot reactor known ZEEP (Zero-energy experimental pile) became the first Canadian reactor, and the first to be completed outside the United States, when it went critical in September 1945. A larger 10 MW NRX reactor which was designed during the war was completed and went critical in July 1947.

Raw materials

A billboard encouraging secrecy amongst Oak Ridge workers.

Nichols arranged with the State Department for export controls to be placed on uranium oxide and negotiated for the purchase of 1,200 tons of ore from the Belgian Congo in a warehouse on Staten Island. He arranged with Eldorado Mining and Refining for the purchase of ore from its mine in Port Hope, Ontario and its shipment in 100-ton lots. Mallinckrodt Incorporated in St Louis, Missouri took the raw ore, dissolved it in nitric acid to produce uranyl nitrate. Ether was then added. As this has a greater affinity for ether than water, and the two liquids do not mix, liquid-liquid extraction was used to separate uranyl nitrate from the impurities. This was then heated to form uranium trioxide, which was reduced to highly pure uranium dioxide. By July 1942, Mallinckrodt was producing a ton of highly pure oxide a day, but turning this into uranium metal initially proved more difficult for Westinghouse and Metal Hydrides. Production was too slow and quality was unacceptably low. A special branch of the Metallurgical Laboratory was established at Iowa State College in Ames, Iowa under Frank Spedding to investigate alternatives. They developed the Ames process, which became available in 1943.

Marshall and Nichols discovered that the electromagnetic process would require 5,000 tons of copper, which was in desperately short supply. However, silver could be substituted, in an 11:10 ratio. On 3 August, Nichols met with Undersecretary of the Treasury Daniel W. Bell and asked for the transfer of 6,000 tons of silver bullion from the West Point Depository. "Young man," Bell told him, "you may think of silver in tons but the Treasury will always think of silver in troy ounces!" Eventually, 14,700 tons would be used. The 1,000-ounce (28,000 g) silver bars were cast into cylindrical billets and taken to Phelps Dodge in Bayway, New Jersey where they were extruded into strips 0.625 inches (15.9 mm) thick, 3 inches (76 mm) wide and 40 feet (12 m) long. These were wound onto magnetic coils by Allis Chalmers in Milwaukee, Wisconsin. After the war, all the machinery was dismantled and cleaned and the floorboards beneath the machinery were ripped up and burned to recover minute amounts of silver. In the end, only 1/36,000th of a percent was lost. The last silver was returned in May 1970.

Uranium

Electromagnetic separation

Natural uranium consists of 99.3% uranium-238 and only 0.7% uranium-235, but only the latter is fissile. The rarer but chemically identical uranium-235 has to be physically separated from the more plentiful isotope. Various physical methods were considered for uranium enrichment, most of which was carried out at Oak Ridge. Electromagnetic isotope separation was developed by Lawrence at the University of California Radiation Laboratory. This method employed devices known as the calutron, which was a hybrid of the familiar laboratory mass spectrometer and cyclotron. The name was derived from the words "California", "university" and "cyclotron". The electromagnetic process was based upon the fact that charged particles are deflected in a magnetic field and the amount of deflection depends upon the particle's mass. The process was neither scientifically elegant nor industrially efficient. Indeed it was reckoned that compared with a gaseous diffusion plant or a nuclear reactor, an electromagnetic separation plant would consume more scarce materials, require more manpower to operate and cost more to build. Nonetheless, it was approved, primarily because it was based on proven technology and therefore represented less risk. Moreover, it could be built in stages and rapidly reach industrial capacity. It also had the backing of Lawrence, the value of which should not be underestimated.

Giant Alpha I racetrack at Y-12.

Responsibility for the design and construction of the electromagnetic separation plant, which came to be called Y-12, was assigned to Stone & Webster by the S-1 Committee in June 1942. The design called for five first stage processing units, known as Alpha racetracks, and two units for final processing, known as Beta racetracks. In September 1943 Groves authorized construction of four more racetracks, known as Alpha II. Construction began in February 1943. Major Wilbur E. Kelley was placed in charge of Y-12. When the plant was started up for testing on schedule in October, the 14-ton vacuum tanks crept out of alignment due to the power of the magnets. As a result, they were fastened more securely. However, a more serious problem arose when the magnetic coils kept shorting out. In December Groves ordered a magnet to be broken open. Kelley reached inside and removed handfuls of rust. Groves then ordered the racetracks to be torn down and all the magnets were sent back to the factory to be cleaned. A pickling plant was established on site to clean the pipes and fittings. As a result, the first Alpha I racetrack was not operational until March 1944. However the second Alpha I was operational by the end of January 1944, the first Beta and third Alpha I came online in March, and the fourth Alpha I was operational in April. The four Alpha II racetracks were completed between July and October 1944.

Operators at their calutron control panels at the Y-12. Gladys Owens, the woman seated in the foreground, did not know what she had been involved with until seeing this photo in a public tour of the facility fifty years later.

Tennessee Eastman was hired to manage Y-12 on the usual cost-plus fixed fee basis, with a fee of $22,500 per month plus $7,500 per racetrack for the first seven racetracks and $4,000 per additional racetrack. The calutrons were initially operated by scientists from Berkeley to remove bugs and achieve a reasonable operating rate. They were then turned over to trained Tennessee Eastman operators who had only a high school education. Nichols compared unit production data, and pointed out to Lawrence that the young "hillbilly" girl operators were outperforming his PhDs. They agreed to a production race and Lawrence lost, a morale boost for the Tennessee Eastman workers and supervisors. The girls were "trained like soldiers not to reason why", while "the scientists could not refrain from time-consuming investigation of the cause of even minor fluctuations of the dials."

Y-12 shipped its first few hundred grams of 13 to 15% enriched uranium to Los Alamos in March 1944. Only 1 part in 5,825 of the uranium feed emerged as final product. Much of the rest was splattered over equipment in the process. Strenuous recovery efforts helped raise the enrichment of the product to 10% in January 1945. Groves was not satisfied and ordered Nichols to remove Kelley. Kelley swapped places with Major John R. Ruhoff, the head of the MED's Manhattan office. In February 1945 the Alpha racetracks began receiving slightly enriched (1.4%) feed from the new S-50 thermal diffusion plant. The next month it received enhanced (5%) feed from the K-25 gaseous diffusion plant. By April K-25 was producing uranium sufficiently enriched to feed directly into the Beta tracks.

Gaseous diffusion

The most promising but also the most challenging method of isotope separation was gaseous diffusion. This is based on Graham's law, which states that the rate of effusion of a gas is inversely proportional to the square root of its molecular mass. In a box containing a semi-permeable membrane and a mixture of two gases, the lighter molecules will pass out of the container more rapidly than the heavier molecules. The gas leaving the container is somewhat enriched in the lighter molecules, while the residual gas is somewhat depleted. The idea was that such boxes could be formed into a cascade of pumps and membranes, with each successive stage containing a slightly more enriched mixture. Research into the process was carried out at Columbia University by a group that included Harold Urey, Karl P. Cohen and John R. Dunning.

Oblique aerial view of an enormous U-shaped building.

Oak Ridge K-25 Plant

In November 1942 the Military Policy Committee approved the constriction of a 600-stage gaseous diffusion plant. On 14 December, M.W. Kellogg accepted an offer to construct the plant, which was codenamed K-25. A cost plus fixed fee contract was negotiated, proving for a fee of $2.5 million. A separate corporate entity called Kellex was created for the project, headed by Percival C. Keith, one of Kellogg's vice presidents. The process faced formidable technical difficulties. The highly corrosive gas uranium hexafluoride would have to be used, as no substitute could be found. The motors and pumps would have to be vacuum tight and enclosed in inert gas. But the biggest problem was the design of the barrier, which would have to be strong, porous and resist to corrosion by uranium hexafluoride. Electro-deposited nickel mesh diffusion barriers were pioneered by Edward Adler and Edward Norris. A six-stage pilot plant was built at Columbia to test the process. Unfortunately, the Norris-Adler prototype proved to be too brittle. A rival barrier was created by Kellex, the Bell Telephone Laboratories and the Bakelite Corporation from nickel powder. In January 1944, Groves ordered the Kellex barrier into production.

Kellex's design for K-25 called for a four-story 0.5 miles (800 m) long U-shaped structure containing 54 contiguous buildings. A survey party began construction by marking out the 500 acres (200 ha) site in May 1943. Work on the main building began in October 1943,and the six-stage pilot plant was ready for operation on 17 April 1944. In 1945 Groves canceled the upper stages of the plant, directing Kellex instead to design and build 540-stage side feed unit, which became known as K-27. Kellex transferred the last unit to the operating contractor, Union Carbide and Carbon on 11 September 1945. The total cost, including K-27 plant which was completed after the war, came to $480 million.

The production plant commenced operation in February 1945, and as cascade after cascade came online, the quality of the product increased. By April 1945, K-25 had attained a 1.1% enrichment and the output of the S-50 thermal diffusion plant began being used as feed. Some nearly 7% product was produced the next month. In August, the last of the 2,892 stages commenced operation. K-25 and K-27 achieved their full potential the early post-war period, when they eclipsed the other production plants and became the prototypes for a new generation of plants.

Thermal diffusion

Main article: S-50 (Manhattan Project)

The thermal diffusion process was developed by US Navy scientists, and was not one of the enrichment technologies initially selected for use in the Manhattan Project. However, in April 1944, Oppenheimer, noting the progress of Philip Abelson's experiments on thermal diffusion at the Naval Research Laboratory, wrote to Groves suggesting that the output of a thermal diffusion plant could be fed into Y-12. Groves set up a committee consisting of Warren K. Lewis, Eger Murphree and Richard Tolman to investigate the idea. They estimated that a thermal diffusion plant costing $3.5 million could enrich 50 kilograms of uranium per week to nearly 0.9% uranium-235. Groves approved its construction on 24 June 1944.

K-25 powerhouse with S-50 plant beyond it, viewed from the air.

Groves contracted with the H.K. Ferguson Company of Cleveland, Ohio, to build the thermal diffusion plant, which was designated S-50. His advisers had estimated that it would take six months to build; Groves gave them just four. Nichols created a special S-50 office within the MED headquarters, headed by Lieutenant Colonel Mark C. Fox, with Major Thomas J. Evans, who would succeed Fox in March 1945, as his deputy. Plans called for the installation of 2,142 48-foot-tall (15 m) diffusion columns arranged in 21 racks. Inside each column were three concentric tubes. Stream obtained from the nearby K-25 powerhouse at a pressure of 100 pounds per square inch (690 kPa) and temperature of 545 °F (285 °C) flowed downward through the innermost 1.25 inches (32 mm) nickel pipe while water at 155 °F (68 °C) flowed upwards through the outermost iron pipe. Isotope separation occurred in uranium hexafluoride between the nickel and copper pipes.

Work commenced on 9 July 1944 and in September, S-50 began partial operation. Furgussen operated the plant through a subsidiary known as Fercleve. The plant produced just 10.5 pounds (4.8 kg) of 0.852% uranium-235 in October. Leaks limited production and forced shut downs over the next months but in June 1945 it produced 12,730 pounds (5,770 kg). By March 1945, all 21 production racks were operating. Initially the output of S-50 was fed into Y-12, but starting in March 1945 all three enrichment processes were run in series. S-50 became the first stage, enriching from 0.71% to 0.89%. This material was fed into the gaseous diffusion process in the K-25 plant, which produced a product enriched to about 23%. This was, in turn, fed into Y-12, which boosted it to about 85%, sufficient for nuclear weapons.

Centrifuge

The centrifuge process was one of the methods regarded as promising in May 1942, but was eliminated by the Military Policy Committee in November 1942 following a recommendation by Conant, Nichols and August C. Klein of Stone & Webster.

Weapon design

Main article: Little Boy

A gun-type nuclear bomb.

The Little Boy uranium bomb was a gun-type fission weapon. It worked by mechanically assembling the critical mass from two subcritical masses of uranium-235: a "bullet" and a "target". The chain reaction resulting from collision of the "bullet" with the "target" released tremendous energy, producing an explosion, but also blew apart the critical mass and ended the chain reaction. The configuration of the critical mass determined how much of the fissile material reacted in the interval between assembly and dispersal, and therefore the explosive yield of the bomb. Even a 1% fission of the material would result in a workable bomb, equal to thousands of tons of high explosive. A poor configuration, or slow assembly, would release enough energy to disperse the critical mass quickly, and the yield would be greatly reduced, equivalent to only a few tons of high explosive.

The method was considered so certain to work that no test was carried out before the bomb was dropped over Hiroshima, although an extensive laboratory testing program was undertaken to make sure the fundamental assumptions were correct. The bomb that was dropped used all the existing extremely highly purified uranium-235, and even most of the less highly purified material, so there was none available for such a test. The bomb's design was known to be inefficient and prone to accidental discharge.

Plutonium

Reactor design

Workers load uranium slugs into the X10 Graphite Reactor

In March 1943, DuPont began construction of the plutonium semiworks on a 112 acres (45 ha) site at Oak Ridge. Intended as a pilot plant for the larger production facilities at Hanford, it included the air cooled X-10 Graphite Reactor, a chemical separation plant, and support facilities. Because of the subsequent decision to construct water cooled reactors at Hanford, only the chemical separation plant operated as a true pilot. The X-10 Graphite Reactor consisted of a huge block of graphite, 24 feet (7.3 m) on each side, weighing around 1,500 tons, surrounded by 7 feet (2.1 m) of high-density concrete as a radiation shield. The greatest difficulty was encountered with the uranium slugs produced by Mallinckrodt and Metal Hydrides. These somehow had to be coated in aluminum to avoid corrosion and the escape of fission products into the cooling system. The Grasselli Chemical Company attempted to develop a hot dipping process without success. Meanwhile Alcoa tried canning. A new process for flux-less welding was developed but the necessary reliability proved elusive. While 97% of the cans passed a standard vacuum test, high temperature tests indicated a failure rate of more than 50%. The Metallurgical Laboratory eventually developed an improved welding technique with the help of General Electric.

Watched by Fermi and Compton, the X-10 Graphite Reactor went critical on 4 November 1943 with about 30 tons of uranium. A week later the load was increased to 36 tons, raising its power generation to 500 KW, and by the end of the month first 500 milligrams (7.7 gr) of plutonium was created. Modifications over time gradually raised the power to 4,000 KW in July 1944. X-10 operated as a production plant until January 1945, when it was turned over to research activities. An air cooled design was chosen for the reactor at Oak Ridge to facilitate rapid construction, but it was recognized that this would be impractical for the much larger production reactors. Initial designs by the Metallurgical Laboratory and DuPont used helium for cooling, but the difficulties led to investigation of alternatives. When it was determined that a water cooled reactor would be simpler, cheaper and quicker to build, this was chosen instead. The design did not become available until 4 October 1943, so in the meantime Matthias concentrated on accommodation, improving the roads, building a railway switch line, upgrading the electricity, water and telephone lines.

Aerial view of Hanford B-Reactor site, June 1944

Work began on the first of three 250 MW reactors, known as Reactor B, on 10 October 1943. Some 390 tons of steel, 17,400 cubic yards (13,300 m³) of concrete, 50,000 concrete blocks and 71,000 concrete bricks were used to construct the 120-foot (37 m) high building. Construction of the reactor itself commenced in February 1944. As at Oak Ridge, most difficulty was encountered with canning the uranium slugs, which commenced at Hanford in March 1944. They were pickled to remove dirt and impurities, dipped in molten bronze, tin, and aluminum-silicon alloy, and canned using hydraulic presses and then capped using arc welding under an argon atmosphere. Finally, they were subjected to a series of tests to detect holes or faulty welds. Disappointingly, most canned slugs initially failed the tests, resulting in an output of only a handful of canned slugs per day. However steady progress was made and by June 1944 production increased to the point where it appeared that enough canned slugs would be available to start the reactor on schedule in August.

Watched by Compton, Matthias, Crawford Greenewalt and Fermi, who inserted the first slug, the process of powering up the reactor commenced on 13 September 1944. Over the next few days, 838 tubes were loaded and the reactor went critical. Shortly after midnight on 27 September, the operators began to withdraw the control rods to initiate production. At first all appeared well but around 03:00 the power level started to drop and by 06:30 the reactor had shut down completely. The cooling water was investigated to see if there was a leak or contamination. The next day the reactor started up again, only to shut down once more. It seemed that the reactor had a half-life of about 9.7 hours. Fermi contacted Chien-Shiung Wu, who identified the cause of the problem as neutron poisoning from xenon-135. Fortunately, DuPont engineer George Graves had deviated from the Metallurgical Laboratory's original design in which the reactor had 1,500 tubes arranged in a circle, and had added an additional 504 tubes to fill in the corners. The scientists had originally considered this overengineering and a waste of time and money, but it was found that by loading all 2,004 tubes and carefully monitoring the power levels, the reactor could reach the required power level and efficiently produce plutonium. Reactor D was started on 17 December 1944 and Reactor F on 25 February 1945.

Thin Man

Thin Man casings. A Fat Man casing is also visible in the photo background.

In 1943, development efforts were directed to a gun-type fission weapon with plutonium called Thin Man. Initial research on the properties of plutonium was done using cyclotron-generated plutonium-239, which was extremely pure, but could only be created in very small amounts. Los Alamos received the first sample of plutonium from the Clinton X-10 reactor in April 1944 and within days Emilio Segrè discovered a problem: the reactor-bred plutonium had a higher concentration of plutonium-240, resulting in up to five times the spontaneous fission rate as cyclotron plutonium. This made reactor plutonium unsuitable for use in a gun-type weapon. The plutonium-240 would start the chain reaction too quickly, causing a predetonation which would release enough energy to disperse the critical mass with a minimal amount of plutonium reacted (a fizzle). A faster gun was suggested but found to be impractical. The possibility of separating the isotopes was considered and rejected, as plutonium-240 is even harder to separate from plutonium-239 than uranium-235 from uranium-238.

Work on an alternative method of bomb design, known as implosion, had begun earlier at the instigation of the physicist Seth Neddermeyer. Implosion would use chemical explosive lenses to inwardly crush a sub-critical sphere of fissile material into a smaller and denser form. When the fissile atoms were packed closer together, the rate of neutron capture would increase, and the mass would become a critical mass. The metal needed to travel only very short distances, so the critical mass would be assembled in much less time than it would take with the gun method. Neddermeyer's 1943 and early 1944 investigations into implosion showed promise, but also made it clear that the problem would be much more difficult from a theoretical and engineering perspective than the gun design. But by July 1944, having concluded plutonium could not be used in a gun design, Oppenheimer abandoned the gun design for the plutonium bomb, in favor of implosion. John von Neumann, who had experience with shaped charges used in armor-piercing shot and shell argued that not only would implosion reduce the danger of predetonation and fizzle, but would make more efficient use of the fissionable material. In August 1944, Oppenheimer implemented a sweeping reorganization of the Los Alamos laboratory to focus on implosion.

Separation process

Meanwhile, the chemists considered the problem of how plutonium could be separated from uranium when its chemical properties were not known. Working with the minute quantities of plutonium available at the Metallurgical Laboratory in 1942, a team under Charles M. Cooper developed a lanthanum fluoride process for separating uranium and plutonium, which was chosen for the pilot separation plant. However Seaborg and Stanly G. Thomson also developed the bismuth phosphate process, and this was considered a good backup process. In May 1943, Greenewalt decided to use the bismuth phosphate process. In the event, both were used in combination. Once X-10 began producing plutonium, the pilot separation plant was put to the test. The first batch was processed at 40% efficiency but over the next few months this was raised to 90%.

Chemical separation plant at Hanford

Early plans called for the construction of two separation plants in the areas known as 200-West and 200-East. This was subsequently reduced to two, the T and U plants, in 200-West and one, the B plant at 200-East. Each separation plant consisted of four buildings: a process cell building or "canyon" (221), a concentration building (224), a purification building (231) and a magazine store (213). The canyons were each 800 feet (240 m) long and 65 feet (20 m) wide. Each consisted of forty 17.7-foot (5.4 m) by 13-foot (4.0 m) by 20-foot (6.1 m) cells. Work began on 221-T and 221-U in January 1944, with the former completed in September and the latter in December. The 221-B building followed in March 1945. Because of the high levels of radioactivity involved, all work in the separation plants had to be conducted by remote control using closed-circuit television. Maintenance was carried out with the aid of an overhead crane and specially designed tools. The 224 buildings were smaller because they had less material to process, and it was less radioactive. The 224-T and 224-U buildings were completed on 8 October 1944, and 224-B followed on 10 February 1945. How the 231-W purification plant was going to work was not known when construction commenced on 8 April 1944, but it was completed by the end of the year. On 5 February 1945, Matthias hand delivered the first shipment of 80 grams (2.8 oz) of 95% pure plutonium nitrate to a Los Alamos courier in Los Angeles.

Metallurgy

The ultimate task of the metallurgists was to figure out how to cast plutonium into a hollow sphere. The difficulties became apparent when attempts to measure the density of plutonium gave inconsistent results. At first contamination was believed to be the cause but it was soon determined that there were multiple allotropes of plutonium. The brittle α phase that exists at room temperature changes to the plastic β phase at higher temperatures. Attention then shifted to the even more malleable δ phase that normally exists in the 300 °C to 450 °C range. It was found that this was stable at room temperature when alloyed with aluminum; but aluminum emits neutrons when bombarded with alpha particles, which would exacerbate the pre-ignition problem. The metallurgists then hit upon plutonium-gallium alloy, which stabilized the δ phase and could be hot pressed into the desired spherical shape. As plutonium was found to corrode readily, the sphere was coated with nickel.

The work proved dangerous. By the end of the war, half the experienced chemists and metallurgists had to be removed from work with plutonium when unacceptably high levels of the element appeared in their urine. A minor fire at Los Alamos in January 1945 led to a fear that a fire in the plutonium laboratory might contaminate the whole town, and Groves authorized the construction of a new facility for plutonium chemistry and metallurgy, which became known as DP-site. The hemispheres for the first plutonium pit were produced and delivered on 2 July 1945. Three more hemispheres followed on 23 July and were delivered three days later.

Weapon design

Main article: Fat Man

An implosion-type nuclear bomb

The accelerated effort on an implosion design, codenamed Fat Man, began in August 1944. The explosives group was headed by George Kistiakowsky. The design of lenses that detonated with just the right shape and velocity turned out to be slow, difficult and frustrating. Various explosives were tested before settling on composition B as the fast explosive and baratol as the slow explosive. Getting the shape just right required fast, reliable and safe electrical detonators. It was therefore decided to use exploding-bridgewire detonators. A contract for their manufacture was given to Raytheon. To study the behavior of converging shock waves, Serber devised the RaLa Experiment, which used the short-lived radioisotope lanthanum-140, a potent source of gamma radiation. With all the effort to avoid predetonation, a method was required to start the chain reaction at precisely the right moment. For this a Polonium-Beryllium modulated neutron initiator was developed. Testing required up to 500 curies per month of Polonium, which fortunately the Monsanto Company was able to deliver.

Trinity

Main article: Trinity (nuclear test)

Because of the complexity of an implosion-style weapon, it was decided that, despite the waste of fissile material, an initial test would be required. Groves approved the test, subject to the active material being recovered. Consideration was therefore given to a controlled fizzle but Oppenheimer soon opted instead for a full-scale explosion inside a containment vessel. This would enable the active material to be recovered in the event of a failure, as Groves did not relish the prospect of explaining the loss of a billion dollars worth of plutonium to a senate committee. Oppenheimer gave the nuclear test the code name "Trinity".

The explosives of the Gadget were raised up to the top of the tower for the final assembly

In March 1944, planning for the test was assigned to Kenneth Bainbridge, a professor of physics at Harvard, working under Kistiakowsky. Bainbridge selected the Alamogordo Bombing Range near Alamogordo Army Airfield as the site for the test. Bainbridge worked with Captain Samuel P. Davalos on the construction of the Trinity Base Camp and its facilities, which included barracks, warehouses, workshops, an explosive magazine and a commissary.

The cylindrical containment vessel, code-named "Jumbo", measuring 25 feet (7.6 m) long and 12 feet (3.7 m) wide, was fabricated at great expense from 214 tons of iron and steel by Babcock & Wilcox in Barberton, Ohio. It was duly brought in a special railroad car to a siding in Pope, New Mexico and was transported the last 25 miles (40 km) from there to the test site on a trailer pulled by two tractors. By the time it arrived confidence in the implosion method was high enough and the availability of plutonium was sufficient enough that Oppenheimer decided not to use it. Instead, it was hoisted up in a steel tower 800 yards (730 m) from the gadget as a rough measure of how powerful the explosion would be. In the end, "Jumbo" survived, though its tower did not, adding credence to the widespread belief that Jumbo would have successfully contained a fizzled explosion.

A pre-test explosion was conducted on 7 May 1945 to calibrate the instruments. A wooden test platform was erected 800 yards (730 m) from Ground Zero and piled with 100 tons of TNT, spiked with nuclear fission products in the form of a molten irradiated uranium slug from Hanford. The test was observed by Oppenheimer and Groves' new deputy commander, Brigadier General Thomas Farrell. It served as a dress rehearsal for the main test. While most of the experiments conducted were of slight value, important lessons were learned concerning the mundane but vital aspects of conducting a test.

For the actual test, the device, nicknamed the gadget, was hoisted to the top of a 100-foot-high steel tower (30 m) for detonation, since this would give a better indication of how the weapon would behave when dropped from a bomber. Detonation in the air maximized the energy applied directly to the target, and generated less nuclear fallout. The gadget was assembled under the supervision of Norris Bradbury at the nearby McDonald Ranch House on 13 July, and precariously winched up the tower the following day. Observers included Bush, Chadwick, Conant, Farrell, Fermi, Groves, Lawrence, Oppenheimer and Tolman. At 05:30 on 16 July 1945 the gadget exploded with an energy equivalent of around 20 kilotons of TNT, leaving a crater of radioactive glass in the desert 250 feet (76 m) wide and 6 feet (1.8 m) deep. The shock wave was felt over 100 miles (160 km) away, and the mushroom cloud reached 7.5 miles (12.1 km) in height. It was heard as far away as El Paso, Texas, so Groves issued a cover story about an ammunition magazine explosion at Alamogordo Field.

Foreign Intelligence

Main article: Operation Alsos

The Manhattan Project was charged with gathering intelligence on the German nuclear energy project. It was believed that the Japanese atomic program was not far advanced because Japan had little access to uranium ore, but it was initially feared that Germany was very close to developing its own weapons. At the instigation of the Manhattan Project, a bombing and sabotage campaign was carried out against heavy water plants in German-occupied Norway. A small mission was created, jointly staffed by Office of Naval Intelligence, OSRD, the Manhattan Project and Army Intelligence (G-2), to investigate enemy scientific developments. It was not restricted to those involving nuclear weapons. The Chief of Army Intelligence, Major General George V. Strong, appointed Lieutenant Colonel Boris T. Pash to command the unit, which was codename "Alsos", a Greek word meaning "grove". As head of the Counter Intelligence Branch of the Western Defense Command, Pash had investigated suspected Soviet espionage at the Radiation Laboratory in Berkeley.

The German experimental nuclear reactor at Haigerloch

The Alsos Mission to Italy questioned staff of the physics laboratory at the University of Rome following the capture of the city in June 1944. Meanwhile Pash formed a second Alsos Mission in London under the command of Captain Horace K. Calvert to participate in Operation Overlord. This mission was to be a combined British and American one. Groves considered the risk that the Germans might attempt to disrupt the Normandy landings with radioactive poisons was sufficient to warn General Dwight D. Eisenhower and send an officer to brief his chief of staff, Lieutenant General Walter Bedell Smith. Under the code-name Operation Peppermint, special equipment was prepared and Chemical Warfare Service teams were trained in its use.

Following in the wake of the advancing Allied armies, Pash and Calvert interviewed Frédéric Joliot-Curie about the activities of German scientists. They spoke to officials at Union Minière du Haut Katangaabout uranium shipments to Germany. They tracked down 68 tons of ore in Belgium and 30 in France. The interrogation of German prisoners indicated that uranium and thorium were being processed in Oranienburg, so Groves arranged for it to be bombed on 15 March 1945. An Alsos team went to Stassfurt in the Soviet Occupation Zone and retrieved 11 tons of ore from WIFO. In April 1945, Pash, in command of a composite force known as T-Force, conducted Operation Harborage, a sweep behind enemy lines of the cities of Hechingen, Bisingen and Haigerloch that were the heart of the German nuclear effort. T Force captured the nuclear laboratories, documents, equipment and supplies, including heavy water and 1.5 tons of metallic uranium.

Alsos teams rounded up German scientists including Kurt Diebner, Otto Hahn, Walther Gerlach, Werner Heisenberg and Carl Friedrich von Weizsäcker, who were taken to England where they were interned at Farm Hall, a bugged house in Godmanchester. After the bombs were detonated in Japan, Heisenberg, by then imprisoned in Britain at Farm Hall with several other nuclear project physicists, almost immediately figured out what the Allies had done, explaining it to his fellow scientists (and the hidden microphones) within days.

Bombing of Hiroshima and Nagasaki

Main article: Atomic bombings of Hiroshima and Nagasaki

Preparations

Groves met with the Chief of United States Army Air Forces (USAAF), General Henry H. Arnold, in March 1944 to discuss the delivery of the finished bombs to their targets. The only Allied aircraft capable of carrying the 17-foot (5.2 m) long Thin Man or the 59-inch (150 cm) wide Fat Man was the British Avro Lancaster, but using a British aircraft would have caused difficulties with maintenance. Groves hoped that the American Boeing B-29 Superfortress could be modified to carry Thin Man by joining its two bomb bays together. Arnold promised that no effort would be spared to modify B-29s to do the job, and designated Major General Oliver P. Echols as the USAAF liaison to the Manhattan Project. Starting in November 1943, the Army Air Forces Materiel Command at Wright Field, Ohio began Silverplate, the modification of B-29s to carry the bombs. Test drops were carried out at Muroc Army Air Field, California.

Silverplate B-29 Straight Flush. Note lack of gun turrets. The tail code of the 444th Bombardment Group is painted on for security reasons.

The 509th Composite Group was activated on 17 December 1944 at Wendover Army Air Field, Utah, under the command of Colonel Paul W. Tibbets. This base close to the border with Nevada was codenamed "Kingman" or "W-47". Training was conducted at Wendover and at Batista Army Airfield, Cuba, where the 393d Bombardment Squadron practiced long distance flights over water. A special unit known as Alberta was formed at Los Alamos under Captain William S. Parsons as part of the Manhattan Project to assist in preparing and delivering the bombs. Commander Frederick L. Ashworth from Alberta met with Fleet Admiral Chester W. Nimitz on Guam in February 1945 to inform him of the project. While he was there, Ashworth selected North Field on Tinian as a base for the 509th Composite Group, and reserved space for the group and its buildings. The group deployed there in July 1945. Farrell arrived on Tinian on 30 July as the Manhattan Project representative.

Most of the components for Little Boy left San Francisco on the cruiser USS Indianapolis on 16 July and arrived on Tinian on 26 July. Four days later the ship was sunk by a Japanese submarine. The remaining components, which included some uranium 235, were delivered by three C-54 aircraft of the Air Transport Command. Two Fat Man assemblies travelled to Tinian in specially modified 509th Composite Group B-29s. The first plutonium core went in a special C-54. A joint Manhattan District-USAAF targeting committee was established to determine which cities in Japan should be targets, which recommended Kokura, Hiroshima, Niigata and Kyoto. At this point, Secretary of War Henry L. Stimson intervened, announcing that he would be making the targeting decision, and that he would not authorize the bombing of Kyoto on the grounds of its historical and religious significance. Groves therefore asked Arnold to remove Kyoto not just from the list of nuclear targets, but from targets for conventional bombing as well. One of Kyoto's substitutes was Nagasaki.

The use of the bombs

President Harry S. Truman, in Europe for the Potsdam Conference, was told that the Trinity test had been successful, and he made an oblique reference to the new weapon to the leader of the Soviet Union, Joseph Stalin. This was the first time that the US had officially notified the Soviet Union about the atomic bomb, although it did not mention its nature. However, Stalin knew of it due to espionage. The authorization to use the bomb against Japan had been given, and the Japanese rejection of the Potsdam Declaration insured that no change would be made to the directive.

On 6 August 1945, 393d Bombardment Squadron B-29 Enola Gay, piloted and commanded by Tibbets lifted off from North Field at 02:45 Tinian time, with Parsons on board as weaponeer, and with the Little Boy weapon in its bomb bay. Hiroshima, an important army depot and port of embarkation, was the primary target of the mission, with Kokura and Nagasaki as alternative targets. With Farrell's permission, Parsons completed the bomb assembly in the air to minimize the risks during takeoff. At 08:09 Tibbets started his bomb run and handed control over to his bombardier, Major Thomas Ferebee. The bomb was released from 31,600 feet (9,600 m) shortly after 09:15 and the aircraft made a 150° bank to maximize the distance between itself and the blast. It detonated at an altitude of 1,750 feet (530 m). The blast was later estimated to be the equivalent of 13 kilotons of TNT (54 TJ). Approximately 4.7 square miles (12 km²) of the city were destroyed. Japanese officials determined that 69% of Hiroshima's buildings were destroyed and another 6–7% damaged. About 70,000 to 80,000 people, or some 30% of the population of Hiroshima, were killed immediately, and another 70,000 injured.

Fat Man explodes over Nagasaki, Japan, August 9, 1945.

On the morning of 9 August 1945, the B-29 Bockscar, piloted by the 393d Bombardment Squadron's commander, Major Charles W. Sweeney, lifted off with a Fat Man on board. This time, Ashworth served as weaponeer and Kokura was the primary target. Sweeney took off with his weapon already armed but with the electrical safety plugs still engaged. When they reached Kokura, they found cloud cover had obscured the city, prohibiting the visual attack required by orders. After three runs over the city, and with fuel running low because a transfer pump on a reserve tank had failed before take-off, they headed for the secondary target, Nagasaki. Fuel consumption calculations made en route indicated that Bockscar would be forced to divert to Okinawa. Ashworth decided that a radar approach would be used if the target was obscured. A last minute break in the clouds over Nagasaki allowed Bockscar's bombardier, Captain Kermit Beahan, to visually sight the target as ordered. The Fat Man was dropped from 29,000 feet (8,800 m) over the city's industrial valley midway between the Mitsubishi Steel and Arms Works in the south and the Mitsubishi-Urakami Ordnance Works in the north. The blast was confined to the Urakami Valley and a major portion of the city was protected by the intervening hills. The resulting explosion had a blast yield equivalent to 21 kilotons of TNT (88 TJ), roughly the same as the Trinity blast. About 44% of the city was destroyed; 35,000 people were killed and 60,000 injured.

Groves expected to have another atomic bomb ready for use on 19 August, with three more in September and a further three in October. Two more Fat Man assemblies were readied. When the Japanese initiated surrender negotiations, Groves ordered the shipments suspended. The third core was scheduled to leave Kirtland Field for Tinian on 12 August. Robert Bacher was packaging it at the Ice House at Los Alamos when he received the word. On 11 August, Groves phoned Warren with orders to organize a survey team to report on the damage and radioactivity at Hiroshima and Nagasaki. A party equipped with portable geiger counters arrived in Hiroshima on 8 September headed by Farrell and Warren, with Japanese Rear Admiral Masao Tsuzuki, who acted as a translator. They remained in Hiroshima until 14 September and then surveyed Nagasaki from 19 September to 8 October.

Post-War

In anticipation of the bombings, Groves had Henry DeWolf Smyth prepare a history for public consumption. Atomic Energy for Military Purposes (better known as the "Smyth Report") was released to the public on 12 August 1945. Groves and Nichols presented Army-Navy "E" Awards to key contractors, whose involvement had hitherto been secret. Over twenty awards of the Presidential Medal for Merit were made to key contractors and scientists, including Bush and Oppenheimer. Military personnel received the Legion of Merit, including the commander of the WAC detachment, Captain Arlene G. Scheidenhelm.

Nichols recommended that S-50 and the Alpha tracks at Y-12 be closed down. This was done in September. Although performing better than ever, the Alpha tracks could not compete with K-25 and the new K-27, which had commenced operation in January 1946. In December, the Y-12 plant was closed, thereby cutting the Tennessee Eastman payroll from 8,600 to 1,500 and saving $2 million a month.

President Harry S Truman signs the Atomic Energy Act of 1946 establishing the United States Atomic Energy Commission

At Hanford, plutonium production fell off as Reactors B, D and F wore out, "poisoned" by fission products and swelling of the graphite moderator known as the Wigner effect. The swelling damaged the charging tubes where the uranium was irradiated to produce plutonium, rendering them unusable. In order to maintain the supply of polonium for the urchin initiators, the oldest unit, B pile, was closed down. Research continued, with DuPont and the Metallurgical Laboratory developing a Redox solvent extraction process as an alternative plutonium extraction technique to the bismuth phosphate process, which left unspent uranium in a state from which it could not easily be recovered.

Bomb engineering was carried out by the Z Division, named for its director, Dr. Jerrold R. Zacharias from Los Alamos. Z Division was initially located at Wendover Field but moved to Oxnard Field, New Mexico in September 1945 to be closer to Los Alamos. This marked the beginning of Sandia Base. Nearby Kirtland Field was used as a B-29 base for aircraft compatibility and drop tests. By October, all the staff and facilities at Wendover had been transferred to Sandia. As reservist officers were demobilized, they were replaced by about fifty hand-picked regular officers.

Nowhere was this more of a problem than at Los Alamos, where there was an exodus of talent. Much remained to be done. The bombs used on Hiroshima and Nagasaki were like laboratory pieces; work would be required to make them simpler, safer and more reliable. There was also a long list of technological improvements, such as applying implosion to uranium in place of the wasteful gun method, and using a composite uranium-plutonium core, now that plutonium was in short supply due to the problems with the reactors. However, uncertainty about the future of the laboratory made it hard to induce them to stay. Oppenheimer returned to his job at the University of California and Groves appointed Norris Bradbury as an interim replacement. In the event, Bradbury world remain in the post for the next 25 years. Groves attempted to combat the dissatisfaction caused by the lack of amenities with a construction program that included an improved water supply, three hundred houses, and recreation facilities.

The wartime Manhattan Project left a legacy in the form of the network of national laboratories: the Lawrence Berkeley National Laboratory, Los Alamos National Laboratory, Oak Ridge National Laboratory, Argonne National Laboratory and Ames Laboratory. Two more were established by the Groves soon after the war, the Brookhaven National Laboratory at Upton, New York and the Sandia National Laboratories at Albuquerque, New Mexico. Groves allocated $72 million to them for research activities in fiscal year 1946–1947. A series of nuclear weapon tests were conducted at Bikini Atoll in July 1946 as part of Operation Crossroads for the purpose of investigating the effect of nuclear weapons on warships. The series consisted of two Fat Man detonations. Able was detonated on 1 July 1946. The more spectacular Baker was detonated underwater on 25 July 1946.

The United States Atomic Energy Commission (AEC) was created by the Atomic Energy Act of 1946 to take over the functions and assets of the Manhattan Project. It established civilian control over atomic development, and separated the development, production and control of atomic weapons from the military. Military aspects were taken over by the Armed Forces Special Weapons Project (AFSWP).

Cost of the Manhattan Project

Costs of the Manhattan Project through 31 December 1945

Site	Cost (1945 USD)
Oak Ridge	$1,188,352,000
Hanford	$390,124,000
Special Operating Materials	$103,369,000
Los Alamos	$74,055,000
Research and Development	$69,681,000
Government Overhead	$37,255,000
Heavy Water Plants	$26,768,000
Total	$1,889,604,000

The project expenditure to 1 October 1945 was $1.845 billion, and was $2.191 billion when the AEC assumed control on 1 January 1947. Total allocation was $2.4 billion. Over 90% of the cost was for building plants and producing the fissionable materials, and less than 10% for development and production of the weapons.

A total of four weapons (the Trinity gadget, Little Boy, Fat Man, and one more unused weapon) were produced by the end of 1945, making the average cost per bomb around $500 million in 1945 dollars. By comparison, the total price by the end of 1945 was about 60% of the total cost spent on all other bombs, mines, and grenades produced; 80% of all small arms materiel (not including ammunition); and 31% of the cost of all tanks produced, all during the same time period.

References

Overall, administrative, and diplomatic histories of the Manhattan Project

• Ahnfeldt, Arnold Lorentz, ed. (1966), Radiology in World War II, Washington, D.C.: Office of the Surgeon General, Department of the Army, OCLC 630225
• Bernstein, Barton J. (June 1976), "The Uneasy Alliance: Roosevelt, Churchill, and the Atomic Bomb, 1940–1945", The Western Political Quarterly (Vol. 29, No. 2), University of Utah: 202–230, retrieved 29 October 2010 {{citation}}: |issue= has extra text (help)
• Bird, Kai; Sherwin, Martin J. (2005), American Prometheus: The Triumph and Tragedy of J. Robert Oppenheimer, New York, New York: Alfred A. Knopf, ISBN 0-375-41202-6, OCLC 56753298
• Fine, Lenore; Remington, Jesse A. (1972), The Corps of Engineers: Construction in the United States, Washington, D.C.: United States Army Center of Military History, OCLC 834187
• Gowing, Margaret (1964), Britain and Atomic Energy, 1935–1945, London: Macmillan Publishing, OCLC 3195209
• Hewlett, Richard G.; Anderson, Oscar E. (1962), The New World, 1939–1946, University Park, Pennsylvania: Pennsylvania State University Press, ISBN 0-520-07186-7, OCLC 637004643
• Holloway, David (1994), Stalin and the Bomb: The Soviet Union and Atomic Energy, 1939–1956, New Haven, Connecticut: Yale University Press, ISBN 0300060564, OCLC 29911222
• Howes, Ruth H.; Herzenberg, Caroline L. (1999), Their Day in the Sun: Women of the Manhattan Project, Philadelphia, Pennsylvania: Temple University Press, ISBN 1-56639-719-7, OCLC 49569088
• Hunner, Jon (2004), Inventing Los Alamos: The Growth of an Atomic Community, Norman, Oklahoma: University of Oklahoma Press, ISBN 978-0-8061-3891-6, OCLC 154690200
• Johnson, Charles; Jackson, Charles (1981), City Behind a Fence: Oak Ridge, Tennessee, 1942–1946, Knoxville, Tennessee: University of Tennessee Press, ISBN 0870493035, OCLC 6331350
• Jones, Vincent (1985), Manhattan: The Army and the Atomic Bomb, Washington, D.C.: United States Army Center of Military History
• Norris, Robert S. (2002), Racing for the Bomb: General Leslie R. Groves, the Manhattan Project's Indispensable Man, South Royalton, Vermont: Steerforth Press, ISBN 1-58642-039-9, OCLC 48544060
• Rhodes, Richard (1986), The Making of the Atomic Bomb, New York, New York: Simon & Schuster, ISBN 0-671-44133-7, OCLC 13793436
• Rhodes, Richard (1995), Dark Sun: The Making of the Hydrogen Bomb, New York, New York: Simon & Schuster, ISBN 0-684-80400-X, OCLC 32509950
• Schwartz, Stephen I. (1998), Atomic Audit: The Costs and Consequences of U.S. Nuclear Weapons, Washington, D.C.: Brookings Institution Press

Technical histories

• Baker, Richard D.; Hecker, Siegfried S.; Harbur, Delbert R. (1983), "Plutonium: A Wartime Nightmare but a Metallurgist's Dream" (PDF), Los Alamos Science (Winter/Spring), Los Alamos National Laboratory: 142–151, retrieved 22 November 2010
• Hansen, Chuck (1995), Swords of Armageddon: U.S. Nuclear Weapons Development since 1945 Volume V: U.S. Nuclear Weapons Histories, Sunnyvale, California: Chukelea Publications
• Hoddeson, Lillian; Henriksen, Paul W.; Meade, Roger A.; Westfall, Catherine L. (1993), Critical Assembly: A Technical History of Los Alamos During the Oppenheimer Years, 1943–1945, New York, New York: Cambridge University Press, ISBN 0-521-44132-3, OCLC 26764320
• Serber, Robert (1992), The Los Alamos Primer: The First Lectures on How to Build an Atomic Bomb, Berkeley, California: University of California Press, ISBN 0-520-07576-5, OCLC 23693470 {{citation}}: |first2= missing |last2= (help); Missing pipe in: |first2= (help)CS1 maint: numeric names: authors list (link) (Available on Wikimedia Commons)
• Ruhoff, John; Fain, Pat (June 1962), "The First Fifty Critical days", Mallinckrodt Uranium Division News (Volume 7, Nos 3 and 4), St Louis, Missouri: Mallinckrodt Incorporated, retrieved 30 October 2010 {{citation}}: |issue= has extra text (help)
• Smyth, Henry DeWolf (1945), Atomic Energy for Military Purposes: the Official Report on the Development of the Atomic Bomb under the Auspices of the United States Government, 1940–1945, Princeton, New Jersey: Princeton University Press, OCLC 770285
• Thayer, Harry (1996), Management of the Hanford Engineer Works In World War II: How the Corps, DuPont and the Metallurgical Laboratory Fast Tracked the Original Plutonium Works, New York, New York: American Society of Civil Engineers Press, ISBN 0-7844-0160-8, OCLC 34323402
• Waltham, Chris (20 June 2002), An Early History of Heavy Water (PDF), Department of Physics and Astronomy, University of British Columbia, retrieved 30 October 2010

Participant accounts

• Bethe, Hans A. (1991), The Road from Los Alamos, New York, New York: Simon and Schuster, ISBN 0-671-74012-1, OCLC 22661282
• Feynman, Richard P. (1997), Surely You're Joking, Mr. Feynman!, New York, New York: W. W. Norton & Company, ISBN 978-0393316049 oclc=10925248 {{citation}}: Check |isbn= value: invalid character (help); Missing pipe in: |ISBN= (help)
• Groves, Leslie (1962), Now it Can be Told: The Story of the Manhattan Project., New York, New York: Harper & Row, ISBN 0-306-70738-1, OCLC 537684
• Libby, Leona Marshall (1979), Uranium People, New York, New York: Charles Scribner's Sons, ISBN 0-684-16242-3, OCLC 4665032
• Nichols, Kenneth David (1987), The Road to Trinity: A Personal Account of How America's Nuclear Policies Were Made, New York, New York: William Morrow and Company, ISBN 0-688-06910-X, OCLC 15223648
• Serber, Robert; Crease, R P (1998), Peace and War: Reminiscences of a Life on the Frontiers of Science, New York, New York: Columbia University Press, ISBN 0-231-10546-0, OCLC 89927303 {{citation}}: |first3= missing |last3= (help); Missing pipe in: |first3= (help)CS1 maint: numeric names: authors list (link)
• Ulam, Stanisław (1983), Adventures of a Mathematician, New York, New York: Charles Scribner's Sons, ISBN 0-520-07154-9, OCLC 1528346