Weapon design
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 of cyclotron plutonium.
This rendered it unsuitable for use in a gun-type weapon, for the plutonium-240 would start the chain reaction too soon, causing a predetonation that would disperse the critical mass after a minimal amount of plutonium had fissioned (a fizzle). A higher-velocity gun was suggested but found to be impractical. The possibility of separating the isotopes was also considered and rejected, as plutonium-240 is even harder to separate from plutonium-239 than uranium-235 from uranium-238, and attempting it "would postpone the weapon indefinitely".
Work on an alternative method of bomb design, known as implosion, had begun earlier under the direction of the physicist Seth Neddermeyer. Implosion used explosives to crush a subcritical sphere of fissile material into a smaller and denser form. The critical mass is assembled in much less time than with the gun method. When the fissile atoms are packed closer together, the rate of neutron capture increases, so it also makes more efficient use of fissionable material. Neddermeyer's 1943 and early 1944 investigations showed promise, but also made it clear that an implosion weapon was more complex than the gun-type design from both a theoretical and an engineering perspective. In September 1943, John von Neumann, who had experience with shaped charges, proposed using a spherical configuration instead of the cylindrical one that Neddermeyer was working on.
An implosion-type nuclear bomb
An accelerated effort on the implosion design, codenamed Fat Man, began in August 1944 when Oppenheimer implemented a sweeping reorganization of the Los Alamos laboratory to focus on implosion. Two new groups were created at Los Alamos to develop the implosion weapon, X (for explosives) Division headed by explosives expert George Kistiakowsky and G (for gadget) Division under Robert Bacher. The new design featured explosive lenses that focused the implosion into a spherical shape. The design of lenses turned out to be slow, difficult and frustrating. Various explosives were tested before settling on composition B and baratol. The final design resembled a soccer ball, with 20 hexagonal and 12 pentagonal lenses, each weighing about 80 pounds (36 kg). Getting the detonation just right required fast, reliable and safe electrical detonators, of which there were two for each lens for reliability. They used exploding-bridgewire detonators, a new invention developed at Los Alamos by a group led by Luis Alvarez.
To study the behavior of converging shock waves, Robert Serber devised the RaLa Experiment, which used the short-lived radioisotope lanthanum-140, a potent source of gamma radiation. The gamma ray source was placed in the center of a metal sphere surrounded by the explosive lenses, which in turn were inside in an ionization chamber. This allowed the taking of an X-ray movie of the implosion. The lenses were designed primarily using this series of tests. In his history of the Los Alamos project, David Hawkins wrote: "RaLa became the most important single experiment affecting the final bomb design".
Within the explosives was an aluminum pusher, which provided a smooth transition from the relatively low-density explosive to the next layer, the tamper of natural uranium. Its main job was to hold the critical mass together as long as possible, but it would also reflect neutrons into the core and some of its uranium would fission. To prevent predetonation by an external neutron, the tamper was coated in a thin layer of neutron-absorbing boron. A polonium-beryllium modulated neutron initiator, known as an "urchin", was developed to start the chain reaction at precisely the right moment.This work on the chemistry and metallurgy of radioactive polonium was directed by Charles Allen Thomas of the Monsanto Company and became known as the Dayton Project. Testing required up to 500 curies per month of polonium, which Monsanto was able to deliver. The whole assembly was encased in a duralumin bomb casing to protect it from bullets and flak.
Remote handling of a kilocurie source of radiolanthanum for a RaLa Experiment at Los Alamos
The ultimate task of the metallurgists was to determine how to cast plutonium into a sphere. The difficulties became apparent when attempts to measure the density of plutonium gave inconsistent results. At first contamination was suspected, 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 using a 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 chemists and metallurgists had to be removed from work with plutonium when unacceptably high levels of the element was detected 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 the DP-site. The hemispheres for the first plutonium pit (or core) were produced and delivered on 2 July 1945. Three more hemispheres followed on 23 July and were delivered three days later.
In contrast to the plutonium Fat Man, the uranium gun-type Little Boy weapon was straightforward if not trivial to design. Overall responsibility for it was assigned to Parsons's Ordnance (O) Division, with the design, development, and technical work at Los Alamos consolidated under Lieutenant Commander Francis Birch's group. The gun-type design now had to work with enriched uranium only, and this allowed the design to be greatly simplified. A high-velocity gun was no longer required, and a simpler weapon was substituted.
Research into the Super was also pursued, although it was considered secondary to the development of a fission bomb. The effort was directed by Teller, who was its most enthusiastic proponent. The F-1 (Super) Group calculated that burning 1 cubic meter (35 cu ft) of liquid deuterium would release the energy of 10 megatonnes of TNT (42 PJ), enough to devastate 1,000 square miles (2,600 km2). In a final report on the Super in June 1946, Teller remained upbeat about the prospect of it being successfully developed, although that opinion was not universal.
Trinity
Because of the complexity of an implosion-style weapon, it was decided that, despite the waste of fissile material, a full-scale nuclear test was required. Oppenheimer codenamed it "Trinity". In March 1944, planning for the test was assigned to Kenneth Bainbridge, who selected the Alamogordo Bombing Range for the test site. A base camp was constructed with barracks, warehouses, workshops, an explosive magazine and a commissary. 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 future Trinity Ground Zero and piled with about 100 short tons (91 t) of high explosives spiked with nuclear fission products.
The explosives of "the gadget" were raised to the top of the tower for the final assembly.
Groves did not relish the prospect of explaining to a Senate committee the loss of a billion dollars worth of plutonium, so a cylindrical containment vessel codenamed "Jumbo" was constructed to recover the active material in the event of a failure. It was fabricated at great expense from 214 short tons (194 t) of iron and steel. By the time it arrived, however, confidence in the implosion method was high enough, and the availability of plutonium was sufficient, that Oppenheimer decided not to use it. Instead, it was placed atop a steel tower 800 yards (730 m) from the weapon as a rough measure of the explosion's power. Jumbo survived, although its tower did not, adding credence to the belief that Jumbo would have successfully contained a fizzled explosion.
The Trinity test of the Manhattan Project was the first detonation of a nuclear weapon.
For the actual test, the weapon, nicknamed "the gadget", was hoisted to the top of a 100-foot (30 m) steel tower, as detonation at that height 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.
At 05:30 on 16 July 1945 the gadget exploded with an energy equivalent of around 20 kilotons of TNT, leaving a crater of trinitite (radioactive glass) in the desert 250 feet (76 m) wide. 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 involving gas shells.
Oppenheimer later claimed that, while witnessing the explosion, he thought of a verse from the Hindu holy book, the Bhagavad Gita (XI,12):
कालोऽस्मि लोकक्षयकृत्प्रवृद्धो लोकान्समाहर्तुमिह प्रवृत्तः। ऋतेऽपि त्वां न भविष्यन्ति सर्वे येऽवस्थिताः प्रत्यनीकेषु योधाः॥११- ३२॥
Translation:
If the radiance of a thousand suns were to burst at once into the sky, that would be like the splendor of the mighty one ...
together with verse (XI,32), which he translated as "Now I am become Death, destroyer of worlds".
The test was significantly more successful than had been anticipated; this was immediately cabled to Stimson, who was then at the Potsdam Conference, and Groves hastily prepared a lengthier report sent via courier. President Harry S. Truman was powerfully and positively affected by the news. Stimson noted in his diary that when he shared it with Churchill, Churchill remarked: "Now I know what happened to Truman yesterday. I couldn't understand it. When he got to the meeting after having read this report, he was a changed man. He told the Russians just where they got on and off and generally bossed the whole meeting."
Personnel
At its peak in June 1944, the Manhattan Project employed about 129,000 workers, of whom 84,500 were construction workers, 40,500 were plant operators and 1,800 were military personnel. As construction activity declined, the workforce fell to 100,000 a year later, but the number of military personnel increased to 5,600. Procuring the required numbers of workers, especially highly skilled workers, in competition with other vital wartime programs proved very difficult. Due to high turnover, over 500,000 people worked on the project. Most African Americans were employed in low-level jobs, but there were a few African-American scientists and technicians. The unique labor and security requirements also resulted in the Manhattan Project having a higher percentage of women in technical roles than later government projects.
In 1943, Groves obtained a special temporary priority for labor from the War Manpower Commission. In March 1944, both the War Production Board and the War Manpower Commission gave the project their highest priority. The Kansas commission director stated that from April to July 1944 every qualified applicant in the state who visited a United States Employment Service office was urged to work at the Hanford Site. No other job was offered until the applicant definitively rejected the offer. Tolman and Conant, in their role as the project's scientific advisers, drew up a list of candidate scientists and had them rated by scientists already working on the project. Groves then sent a personal letter to the head of their university or company asking for them to be released for essential war work.
A large crowd of men and women in uniform listens to a fat man in uniform speaking at a microphone. They are wearing the Army Service Forces sleeve patch. The women are at the front and the men at the back. Beside him is the flag of the Army Corps of Engineers. Behind them are wooden two-storey buildings.
One source of skilled personnel was the Army itself, particularly the Army Specialized Training Program. In 1943, the MED created the Special Engineer Detachment (SED), with an authorized strength of 675. Technicians and skilled workers drafted into the Army were assigned to the SED. Another source was the Women's Army Corps (WAC). Initially intended for clerical tasks handling classified material, the WACs were soon tapped for technical and scientific tasks as well. On 1 February 1945, all military personnel assigned to the MED, including all SED detachments, were assigned to the 9812th Technical Service Unit, except at Los Alamos, where military personnel other than SED, including the WACs and Military Police, were assigned to the 4817th Service Command Unit.
An associate professor of Radiology at the University of Rochester School of Medicine, Stafford L. Warren, was commissioned as a colonel in the United States Army Medical Corps, and appointed as chief of the MED's Medical Section and Groves' medical advisor. Warren's initial task was to staff hospitals at Oak Ridge, Richland and Los Alamos. The Medical Section was responsible for medical research, but also for the MED's health and safety programs. This presented an enormous challenge, because workers were handling a variety of toxic chemicals, using hazardous liquids and gases under high pressures, working with high voltages, and performing experiments involving explosives, not to mention the largely unknown dangers presented by radioactivity and handling fissile materials. Yet in December 1945, the National Safety Council presented the Manhattan Project with the Award of Honor for Distinguished Service to Safety in recognition of its safety record. Between January 1943 and June 1945, there were 62 fatalities and 3,879 disabling injuries—about 62 percent below the rate of private industry.
Secrecy
The Manhattan Project operated under a mandate of "absolute secrecy" from Roosevelt, meaning that the very existence of the project itself was to be kept secret. This proved a daunting task given the amount of knowledge and speculation about nuclear fission that existed prior to the Manhattan Project, the huge numbers of people involved, and the scale of the facilities. Groves adopted an extreme version of compartmentalization (the need-to-know policy):
Compartmentalization of knowledge, to me, was the very heart of security. My rule was simple and not capable of misinterpretation—each man should know everything he needed to know to do his job and nothing else. Adherence to this rule not only provided an adequate measure of security, but it greatly improved over-all efficiency by making our people stick to their knitting. And it made quite clear to all concerned that the project existed to produce a specific end product—not to enable individuals to satisfy their curiosity and to increase their scientific knowledge.
This clashed with the norms of many of the scientists involved, who claimed that science could not operate successfully under such requirements. The Manhattan Project officials also had difficulty with journalists, Congressmen, federal officials who were not "in the know", residents near local sites, judges adjudicating land claims, and other sources of speculation, prying, and leaks, along with concerns about espionage and sabotage. Groves relied on the FBI and his own autonomous G-2 intelligence unit to investigate potential security violations. Ultimately over 1,500 "loose talk" cases were investigated during the war.
Because of its relative success at keeping the story out of newspapers, Byron Price, head of the Office of Censorship, ultimately designated the Manhattan Project "the best-kept secret of the war". In 1945 Life estimated that before the Hiroshima and Nagasaki bombings "probably no more than a few dozen men in the entire country knew the full meaning of the Manhattan Project, and perhaps only a thousand others even were aware that work on atoms was involved." The magazine wrote that the more than 100,000 others employed with the project "worked like moles in the dark". Warned that disclosing the project's secrets was punishable by 10 years in prison or a fine of US$10,000 (equivalent to $175,000 in 2024), they monitored "dials and switches while behind thick concrete walls mysterious reactions took place" without knowing the purpose of their jobs.
In December 1945 the US Army published a secret report assessing the security apparatus surrounding the Manhattan Project. The report states that the project was "more drastically guarded than any other highly secret war development." The surrounding security infrastructure was so vast and thorough that in the early days of the project in 1943, investigators vetted 400,000 potential employees and 600 companies for potential security risks.
Censorship
Voluntary censorship of atomic information began before the Manhattan Project. After the start of the European war in 1939 American scientists began avoiding publishing military-related research, and in 1940 scientific journals began asking the National Academy of Sciences to clear articles. William L. Laurence of The New York Times, who wrote an article on atomic fission in The Saturday Evening Post of 7 September 1940, later learned that government officials asked librarians nationwide in 1943 to withdraw the issue. The Soviets noticed the silence, however. In April 1942 nuclear physicist Georgy Flyorov wrote to Joseph Stalin on the absence of articles on nuclear fission in American journals; this resulted in the Soviet Union establishing its own atomic bomb project.
The Manhattan Project operated under tight security lest its discovery induce Axis powers, especially Germany, to accelerate their own nuclear projects or undertake covert operations against the project. The Office of Censorship relied on the press to comply with a voluntary code of conduct it published, and the project at first avoided notifying the office. By early 1943 newspapers began publishing reports of large construction in Tennessee and Washington, and the office began discussing with the project how to maintain secrecy. In June it asked newspapers and broadcasters to avoid discussing "atom smashing, atomic energy, atomic fission, atomic splitting, or any of their equivalents. The use for military purposes of radium or radioactive materials, heavy water, high voltage discharge equipment, cyclotrons."
Soviet spies
The prospect of sabotage was always present, and sometimes suspected when there were equipment failures. While there were some problems believed to be the result of careless or disgruntled employees, there were no confirmed instances of Axis-instigated sabotage. However, on 10 March 1945, a Japanese fire balloon struck a power line, and the resulting power surge caused the three reactors at Hanford to be temporarily shut down. With so many people involved, security was difficult. A special Counter Intelligence Corps detachment was formed to handle the project's security issues. By 1943, it was clear that the Soviet Union was attempting to penetrate the project. Lieutenant Colonel Boris T. Pash, the head of the Counter Intelligence Branch of the Western Defense Command, investigated suspected Soviet espionage at the Radiation Laboratory in Berkeley. Oppenheimer informed Pash that he had been approached by a fellow professor at Berkeley, Haakon Chevalier, about passing information to the Soviet Union.
The most successful Soviet spy was Klaus Fuchs, a physicist and member of the British Mission who was intimately involved in work at Los Alamos on the design of the implosion bomb. His espionage activities were not identified until 1950, as a result of Venona project. The revelation of his espionage activities damaged the United States' nuclear cooperation with Britain and Canada, and other instances of espionage were subsequently uncovered, leading to the arrest of Harry Gold, David Greenglass, and Julius and Ethel Rosenberg. Other spies like George Koval and Theodore Hall remained unknown for decades. The value of the espionage is difficult to quantify, as the principal constraint on the Soviet atomic bomb project was their short supply of uranium ore. It may have saved the Soviets at least one or two years in the development of their own bomb, although some historians have argued the Soviets spent as much time vetting and reduplicating the information as they would have saved had they trusted it.
Foreign intelligence
In addition to developing the atomic bomb, the Manhattan Project was charged with gathering intelligence on the German nuclear energy project. It was believed that the Japanese nuclear weapons 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 the 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 Boris Pash to command the unit, which was codenamed "Alsos" (Greek for "grove"). Samuel Goudsmit was the scientific director of the Alsos mission.
Soldiers and workmen, some wearing steel helmet, clamber over what looks like a giant manhole.
Allied soldiers dismantle the German experimental nuclear reactor at Haigerloch.
The Alsos Mission to Italy questioned physics laboratory staff at the University of Rome following the capture of the city in June 1944. Meanwhile, Pash formed a combined British and American Alsos mission in London under the command of Captain Horace K. Calvert to participate in Operation Overlord. 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 codename 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, the Alsos team interrogated scientists and searched facilities in liberated areas of France and Germany to learn about the German work. Goudsmit concluded in November 1944 that the German nuclear program had never made it beyond the laboratory stage. As he put it later: "The evidence at hand proved definitely that Germany had no atom bomb and was not likely to have one in any reasonable time."
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 to deny its capture by the Soviet Union. 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 Hechingen, Bisingen, and Haigerloch—the heart of the German nuclear effort. T-Force captured 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. They were taken to England and interned at Farm Hall, where they were surreptitiously surveilled.
Atomic bombings of Hiroshima and Nagasaki
Preparations
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 a Thin Man by joining its two bomb bays together. This became unnecessary after Thin Man was abandoned, as a Little Boy was short enough to fit into a B-29 bomb bay, but modifications were still required. The Army Air Forces Materiel Command at Wright Field, Ohio, began Silverplate, the codename for the modification of the B-29, in November 1943. Test drops were carried out at Muroc Army Air Field and the Naval Ordnance Test Station in California with Thin Man and Fat Man pumpkin bombs to test their ballistic, fuzing and stability characteristics.
The 509th Composite Group was activated on 17 December 1944 at Wendover Army Air Field, Utah, under the command of Colonel Paul W. Tibbets. Its 393rd Bombardment Squadron, equipped with Silverplate B-29s, practiced long-distance flights over water and dropped pumpkin bombs. A special unit known as Project Alberta was formed at Los Alamos under Parsons's command to assist in preparing and delivering the bombs. The 509th Composite Group deployed to North Field on Tinian in July 1945. Most of the components for the Little Boy left San Francisco on the cruiser USS Indianapolis on 16 July and arrived on Tinian on 26 July. The remaining components, which included six highly enriched uranium rings, were delivered by three Douglas C-54 Skymasters of the 509th Group's 320th Troop Carrier Squadron. Two Fat Man assemblies traveled to Tinian in specially modified 509th Composite Group B-29s, and the first plutonium core went in a special C-54.
At the end of December 1944, worried by the heavy losses occurring in the Battle of the Bulge, Roosevelt instructed Groves and Stimson that if the atomic bombs were ready before the war with Germany ended, they should be ready to drop them on Germany, but Japan was regarded as more likely. In late April 1945, a targeting committee was established to determine which cities should be targets, and it recommended Kokura, Hiroshima, Niigata, and Kyoto. 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. Nagasaki was ultimately substituted. In May 1945, the Interim Committee was created to advise on wartime and postwar use of nuclear energy. The Interim Committee in turn established a scientific panel consisting of Arthur Compton, Fermi, Lawrence, and Oppenheimer; the scientific panel offered its opinion not just on the likely physical effects of an atomic bomb, but on its probable military and political impact. In a meeting on 1 June, the Interim Committee resolved that "the bomb should be used against Japan as soon as possible; that it be used on a war plant surrounded by workers' homes; and that it be used without prior warning".
At the Potsdam Conference in Germany, President Harry S. Truman told Stalin that the US had "a new weapon of unusual destructive force", without giving any details. As he showed "no special interest," Truman erroneously assumed that Stalin did not understand. In reality, Soviet spies had kept Stalin informed of the work and the planned test.
A strike order from General Thomas T. Handy to General Carl Spaatz was approved by Marshall and Stimson on 25 July which specified that the "first special bomb" be used "after about 3 August 1945," and that "additional bombs" would be used "as soon as made ready by the project staff". The operational plan was to drop the first bomb on 2 August, the second bomb on 10 August, and a third bomb around 24 August. However, due to weather conditions over Japan and the desire for visual bombing, the date of the first bombing mission was pushed back to 6 August, and the second was moved forward to 9 August.
Bombings
On 6 August 1945, the Enola Gay, a Boeing B-29 Superfortress of the 393d Bombardment Squadron, piloted by Tibbets, lifted off from North Field with a Little Boy in its bomb bay. Hiroshima, the headquarters of the 2nd General Army and Fifth Division and a port of embarkation, was the primary target, with Kokura and Nagasaki as alternatives. Parsons, the weaponeer in charge of the mission, completed the bomb assembly in the air to minimize the risks of a nuclear explosion in the event of a crash during takeoff. The bomb detonated at an altitude of 1,750 feet (530 m) with a blast that was later estimated to be the equivalent of 13 kilotons of TNT. An area of approximately 4.7 square miles (12 km2) was destroyed. Japanese officials determined that 69% of Hiroshima's buildings were destroyed and another 6–7% damaged. Early estimates were that 66,000 people were killed and 69,000 injured; later re-estimations that included people ignored by previous methods, like Korean slave laborers and additional soldiers, concluded there might have been 140,000 dead from the attack by December 1945.
On the morning of 9 August 1945, the Bockscar, a second B-29 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. When they reached Kokura, they found cloud cover had obscured the city, prohibiting the visual attack required by orders. After three runs and with fuel running low, they headed for the secondary target, Nagasaki. Ashworth decided that a radar approach would be used if the target was obscured, but a last-minute break in the clouds over Nagasaki allowed a visual approach as ordered. The Fat Man was dropped 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 resulting explosion had a blast yield equivalent to 21 kilotons of TNT, roughly the same as the Trinity blast, but was confined to the Urakami Valley, and a major portion of the city, including the city center, was protected by the intervening hills. About 44% of the city was destroyed, and estimates of casualties range from 40,000 to 80,000 people killed and at least 60,000 injured. Overall, an estimated 35,000–40,000 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, and scheduled to leave Kirtland Field for Tinian on 11 and 14 August. At Los Alamos, technicians worked 24 hours straight to cast another plutonium core. Although cast, it still needed to be pressed and coated, which would take until 16 August. It could therefore have been ready for use on 19 August.
On 10 August, Truman was informed that another bomb was being prepared. He ordered that no additional atomic bombs could be used without his express authority. According to Henry A. Wallace, Truman told his cabinet that "the thought of wiping out another 100,000 people was too horrible. He didn't like the idea of killing, as he said, 'all those kids.'" Groves suspended the third core's shipment on 13 August.
On 11 August, Groves phoned Warren with orders to organize a survey team to report on the damage and radioactivity at Hiroshima and Nagasaki as soon as the war ended. 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. This and other scientific missions to Japan provided valuable data on the effects of the atomic bomb, and led to the creation of the Atomic Bomb Casualty Commission.
In anticipation of the bombings, Groves had commissioned physicist Henry DeWolf Smyth to prepare a sanitized technical history of the project for public consumption. The idea of releasing such information freely was controversial; the decision to do so was made by Truman personally. The "Smyth Report" was released to the public on 12 August 1945.
Japan announced its surrender on 15 August. The necessity of the bombings became a subject of controversy among historians. Some questioned whether "atomic diplomacy" would have attained the same goals, and the relative weight that the bombs and the Soviet declaration of war had on the Japanese willingness to surrender. The Franck Report was the most notable effort pushing for a demonstration but was turned down by the Interim Committee's scientific panel.The Szilárd petition, drafted in July 1945 and signed by dozens of scientists working on the Manhattan Project, was a late attempt at warning Truman about his responsibility in using such weapons.
After the war
The Manhattan Project became instantly famous after the bombing of Hiroshima and the partial lifting of its secrecy. It was widely credited with ending the war, and Groves worked to credit its contractors, whose work had hitherto been secret. Groves and Nichols presented them with Army–Navy "E" Awards, and over 20 Presidential Medals for Merit were awarded to key contractors and scientists, including Bush and Oppenheimer. Military personnel received the Legion of Merit.
The Manhattan Project persisted until 31 December 1946, and the Manhattan District to 15 August 1947. During this time, it suffered from numerous difficulties caused by technical problems, the effects of rapid demobilization, and a lack of clarity on its long-term mission.
At Hanford, plutonium production declined 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. Production was curtailed and the oldest unit, B pile, was closed down so at least one reactor would remain available. 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, 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 the Sandia Base. Nearby Kirtland Field was used as a B-29 base for aircraft compatibility and drop tests. As reservist officers were demobilized, they were replaced by about fifty hand-picked regular officers.
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, cutting the Tennessee Eastman payroll from 8,600 to 1,500 and saving $2 million a month.
Nowhere was demobilization 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 needed work to make them simpler, safer and more reliable. Implosion methods needed to be developed for uranium in place of the wasteful gun method, and composite uranium-plutonium cores were needed now that plutonium was in short supply. However, uncertainty about the future of the laboratory made it hard to induce people to stay. Oppenheimer returned to his job at the University of California and Groves appointed Norris Bradbury as an interim replacement; Bradbury remained 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.
Manhattan Project personnel participated in the first postwar nuclear tests, Operation Crossroads, conducted at Bikini Atoll in July 1946. Two Fat Man-type bombs were detonated — one as an airburst, one as an underwater burst — to investigate the effect of nuclear weapons on warships. Press and international observers were allowed to attend, making the tests an international spectacle.
Following a domestic debate over the peacetime management of the nuclear program, the Atomic Energy Act of 1946 created the United States Atomic Energy Commission to take over the project's functions and assets. It established civilian control over atomic development. Military aspects were taken over by the Armed Forces Special Weapons Project (AFSWP).
After the bombings at Hiroshima and Nagasaki, a number of Manhattan Project physicists founded the Bulletin of the Atomic Scientists (1945) and Emergency Committee of Atomic Scientists (1946), which began as an emergency action undertaken by scientists who saw urgent need for an educational program about atomic weapons. In the face of the destructiveness of the bombs and in anticipation of the nuclear arms race several project members including Bohr, Bush and Conant expressed the view that it was necessary to reach agreement on international control of nuclear research and atomic weapons. The Baruch Plan, unveiled in a speech to the newly formed United Nations Atomic Energy Commission (UNAEC) in June 1946, proposed the establishment of an international atomic development authority, but was not adopted.
Cost
Manhattan Project costs through 31 December 1945
Site Cost (1945 USD, millions) Cost (2023 USD, millions) % of total
Oak Ridge $1,188 $15,949 62.9%
Hanford $390 $5,236 20.6%
Special operating materials $103 $1,387 5.5%
Los Alamos $74 $994 3.9%
Research and development $70 $935 3.7%
Government overhead $37 $500 2.0%
Heavy water plants $27 $359 1.4%
Total $1,890 $25,361
The project expenditure through 1 October 1945 was $1.845 billion, equivalent to less than nine days of wartime spending, and was $2.191 billion when the AEC assumed control on 1 January 1947. The total allocation was $2.4 billion. 84% of the costs through the end of 1945 were spent on the plants at Oak Ridge and Hanford, producing the enriched uranium and plutonium needed to fuel the bombs. At both sites, the majority of the costs were for construction (74% at Oak Ridge, 87% at Hanford), with the rest being for operations.
Initial funding for the project was through the general budget of the Office of Scientific Research and Development. As plans were made to turn the work over to the Army Corps of Engineers, Bush wrote to Roosevelt in late 1942 that "it would be ruinous to the essential secrecy to have to defend before an appropriations committee any request for funds for this project." Instead, initial funding was done through discretionary funds to which Roosevelt had access.
As it grew in size and cost, Congress was deliberately kept ignorant of the project, because of concerns that Congressmen were prone to leaking information, and because it was feared that the project would appear to be a boondoggle. Appropriations requests were quietly slipped into other bills, but the project's mounting costs and large facilities (which appeared to many to produce nothing) attracted scrutiny from several Congressional auditors. The Truman Committee that investigated wartime waste and fraud attempted to audit the project several times, but each time their inquiries were rejected.
These Congressional inquiries, along with the need for smooth budgetary approval, led to Bush, Groves, and Stimson agreeing in the spring of 1944 that a few high-ranking Congressmen should be told of the project's purpose. By March 1945, exactly seven Congressmen were officially informed. The funds were hidden into appropriation requests with the inconspicuous headings, frequently "Engineer Service Army" and "Expediting Production." In late May 1945, to further expedite budget issues and assure the cooperation of Albert J. Engel, who had threatened to reveal the existence of the project if he was not told more about it, five additional Congressmen were permitted to visit the Oak Ridge site to assure themselves of "the reasonableness of the various living accommodations which had been provided, [and] that they actually observe the size and scope of the installations and that some of the complexities of the project be demonstrated to them."
During the war, the Manhattan Project ultimately produced the three bombs used (the Trinity gadget, Little Boy, and Fat Man), as well as an additional unused Fat Man bomb, making the average wartime cost per bomb around $500 million in 1945 dollars. By comparison, the project's total cost by the end of 1945 was about 90% of the total spent on the production of US small arms (not including ammunition) and 34% of the total spent on US tanks during the same period. It was the second most expensive weapons project undertaken by the United States during the war, behind only the Boeing B-29 Superfortress.
Legacy
The Lake Ontario Ordnance Works (LOOW) near Niagara Falls became a principal repository for Manhattan Project waste for the Eastern United States. All of the radioactive materials stored at the LOOW site—including thorium, uranium, and the world's largest concentration of radium-226—were buried in an "Interim Waste Containment Structure" (in the foreground) in 1991.
The political and cultural impacts of the development of nuclear weapons were profound. William Laurence of The New York Times, the first to use the phrase "Atomic Age", became the official correspondent for the Manhattan Project in spring 1945. He witnessed both the Trinity test and the bombing of Nagasaki and wrote the official press releases on them. He went on to write a series of articles extolling the virtues of the new weapon. His reporting helped to spur public awareness of the potential of nuclear technology and motivated its development in the United States and Soviet Union.
The Manhattan Project left a legacy of a 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 Groves soon after the war, the Brookhaven National Laboratory at Upton, New York, and the Sandia National Laboratories at Albuquerque, New Mexico. They would be in the vanguard of the kind of large-scale research that Alvin Weinberg, the director of the Oak Ridge National Laboratory, would call Big Science. Computational science, especially computational engineering, was influenced by the Manhattan Project; Los Alamos ran one of the most advanced tabulating machine facilities in the world.
The Naval Research Laboratory had long been interested in the prospect of using nuclear power for warship propulsion, and sought to create its own nuclear project. In May 1946, Nimitz, now Chief of Naval Operations, decided that the Navy should instead work with the Manhattan Project. A group of naval officers were assigned to Oak Ridge, the most senior of whom was Captain Hyman G. Rickover, who became assistant director there. They immersed themselves in the study of nuclear energy, laying the foundations for a nuclear-powered navy. A similar group of Air Force personnel arrived at Oak Ridge in September 1946 with the aim of developing nuclear aircraft. Their Nuclear Energy for the Propulsion of Aircraft project ran into formidable technical difficulties and was ultimately canceled.
The ability of the new reactors to create radioactive isotopes in previously unheard-of quantities sparked a revolution in nuclear medicine. Starting in mid-1946, Oak Ridge began distributing radioisotopes to hospitals and universities, primarily iodine-131 and phosphorus-32 for cancer diagnosis and treatment. Isotopes were also used in biological, industrial and agricultural research.
Its production sites, operating with new technologies, exotic substances, and under conditions of secrecy and haste, also left a vast legacy of waste and environmental damage. At Hanford, for example, corrosive and radioactive wastes were stored in "hastily fabricated, single-shell, steel-lined, underground storage tanks" that were intended to be temporary, awaiting a more permanent solution. Instead, they were neglected and eventually leaked. Issues of this kind resulted in Hanford becoming "one of the most contaminated nuclear waste sites in North America", and the subject of significant cleanup efforts after it was deactivated in the late Cold War.
On handing over control to the Atomic Energy Commission, Groves bid farewell to the people who had worked on the Manhattan Project:
Five years ago, the idea of Atomic Power was only a dream. You have made that dream a reality. You have seized upon the most nebulous of ideas and translated them into actualities. You have built cities where none were known before. You have constructed industrial plants of a magnitude and to a precision heretofore deemed impossible. You built the weapon which ended the War and thereby saved countless American lives. With regard to peacetime applications, you have raised the curtain on vistas of a new world.
The Manhattan Project National Historical Park was established on 10 November 2015.
Notes
Specifically at its Berkeley campus; however, as of 1940, the University of California had not yet established a formal distinction between the university as a whole and its flagship campus at Berkeley. The process of transforming the University into a multi-campus university system began in March 1951 and was not complete until 1960.
The reaction Teller was most concerned with was: 14
7N + 14
7N → 24
12Mg + 4
2He (alpha particle) + 17.7 MeV.
In Bethe's account, the possibility of this ultimate catastrophe came up again in 1975 when it appeared in a magazine article by H.C. Dudley, who got the idea from a report by Pearl Buck of an interview she had with Arthur Compton in 1959. The worry was not entirely extinguished in some people's minds until the Trinity test.
Sundt Construction Co., the general contractor and construction company responsible for Los Alamos.
Natural self-sustaining nuclear reactions have occurred in the earth's crust in the very distant past.
The allusion here is to the Italian navigator Christopher Columbus, who reached the Caribbean in 1492.
The original project goal in 1942 was to acquire approximately 1,700 short tons (1,500 t) of uranium ore. By the time of the dissolution of the Manhattan District, it had acquired about 10,000 short tons (9,100 t) tons of uranium oxides, 72% of which came from the Congolese ores, 14% from the Colorado plateau, and 9% from Canadian ores.
Much of the mined ore from the Shinkolobwe mine had a uranium oxide content as high as 65% to 75%, which was many times higher than any other global sources. By comparison, the Canadian ores could be as high as 30%, and American sources, many of them byproducts of the mining of other minerals (especially vanadium), contained less than 1% uranium.
It is necessary to distinguish between the K-25 gaseous diffusion plant and the K-25 power plant. The latter provided energy to both the K-25 gaseous diffusion plant and the S-50 thermal diffusion plant.
The charge consisted of 89.75 short tons (81.42 t) tons of TNT and 14.91 short tons (13.53 t) tons of Composition B (with the total explosive power of approximately 108 tons of TNT), actually a few tons more than the stated "100-tons".
The first instance in print of Oppenheimer's Gita story is apparently from 1948. Oppenheimer at times translated it to "shatterer of worlds" as well. The quote with "destroyer of worlds" comes from a taped interview of Oppenheimer did with NBC in 1965. Oppenheimer's translation is not considered a standard or literal one, and was likely influenced by the style of his Sanskrit teacher, Arthur Ryder, who translated the line as: "Death am I, and my present task / Destruction." A more common translation has the identification not as "Death," but as "Time." In the passage, the Hindu god Krishna is revealing himself and his true form to Prince Arjuna, imploring Arjuna to fulfill his duty and take part in a war, and assuring him that the fate of those killed is really up to Krishna, not mortal men.
The seven Congressmen officially informed were: Alben W. Barkley (Senate Majority Leader), Styles Bridges (Ranking minority member of the Sub-Committee on Military Appropriations), Joseph W. Martin Jr. (House Minority Leader), John W. McCormack (House Majority Leader), Sam Rayburn (Speaker of the House), Elmer Thomas (Chair of the Sub-Committee on Military Appropriations), and Wallace H. White (Senate Minority Leader). The five allowed to tour Oak Ridge were: Clarence Cannon, Albert J. Engel, George H. Mahon, J. Buell Snyder, and John Taber.
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