The short march to China’s hydrogen bomb

By Hui Zhang

The June 17, 1967 nuclear test was the culmination of China's breakneck development of the hydrogen bomb. (via UCSB)

The short march to
China's hydrogen bomb

April 11, 2024

On December 28, 1966, China successfully conducted its first hydrogen bomb test—only two years and two months after the successful explosion of its first atomic bomb. In so doing, China became the fastest among the five initial nuclear-weapon states (the United States, Russia, China, the United Kingdom, and France, collectively known as P5) to pass from its first atomic bomb explosion to a first hydrogen bomb detonation.

There is still very limited knowledge in Western literature about how China built its first H-bomb. Based on newly available information—including Chinese blogs, memoirs, and other publicly available publications—this account reconstructs the history of how China made a breakthrough in understanding hydrogen bomb principles and built its first H-bomb—without foreign help.

Beyond the previously untold story of China’s early exploration of the hydrogen bomb theory, the article also explores in detail the so-called “100 days in Shanghai”—a milestone of China’s hydrogen bomb development—and describes the efforts that led to a series of three nuclear tests that happened in 1966 and 1967 and that are often called “the trilogy” of the H-bomb development in China.

Early explorations

https://thebulletin.org/wp-content/uploads/2024/04/meng-zhaorui.jpg
Raising the Little Red Book in celebration of China’s first atomic bomb test on October 16, 1964. (Photo by Meng Zhaorui)

October 1957
to June 1959

Moscow’s broken promise

China officially started its nuclear weapon program on January 15, 1955.[1] About two years later, China and the Soviet Union signed the New Defense Technical Accord in Moscow. Under that agreement, Moscow would provide Beijing with a prototype of an atomic bomb model and relevant technical materials. In June 1959, however, as many major relevant facilities in the Chinese nuclear weapon program were at the peak of construction, Soviet-Sino relations deteriorated,[2] and Moscow sent a letter to Beijing formally announcing it would not provide the promised model and data. From the second half of 1959 onward, the Second Ministry of Machine Building Industry—China’s government ministry overseeing the nuclear industry—followed central government policy and relied on the country’s own capabilities to complete the task of developing the atomic bomb.[3]

In early 1960, the weaponeers of the Beijing institute of nuclear weapon research—called the Ninth Institute and placed under the leadership of the Second Ministry[4]—started to explore atomic bomb science and technology. As those weaponeers started working hard on the atomic bomb program, then-Minister of the Second Ministry Liu Jie began considering ways to conduct the nation’s hydrogen bomb development. Before this, he had participated in the negotiation of the 1957 agreement with the Soviet government. In addition to information about the atomic bomb, under the agreement China was also supposed to receive a sample of a boosted nuclear bomb, specifically a “layer-cake” bomb.[5]

Liu understood that the boosted nuclear bomb provided by Moscow would be an atomic bomb, not a hydrogen bomb.[6] He sensed hydrogen bombs and atomic bombs could be very different in principle and structure. (An atomic bomb uses uranium or plutonium and relies on fission, a nuclear reaction that splits an atom or nucleus and releases a large amount of energy; a hydrogen bomb or H-bomb uses fission to trigger a fusion reaction that combines two atomic nuclei to form a single heavier nucleus, releasing a much larger amount of energy.) When the leader of the Soviet expert team was visiting the Second Ministry, Liu took the opportunity to ask him questions about the difference in principle and structure between the hydrogen bomb and the atomic bomb. But none of the responses he received satisfied him.[7] Liu understood that the Soviet Union would not share the hydrogen bomb technology with China. Liu therefore realized that it would take a significant amount of time to make breakthroughs in the theory of the hydrogen bomb and thought the start of this work could not wait until after the success of the first Chinese atomic bomb.

[1] China’s official nuclear history is Li Jue, Lei Rongtian, Li Yi, and Li Yingxiang, eds., China Today: Nuclear Industry, China Social Science Press, Beijing, 1987 (in Chinese), p. 13-14.

[2] Shen Zhihua and Yafeng Xia, Between Aid and Restriction: Changing Soviet Policies toward China’s Nuclear Weapons Program: 1954-1960, Nuclear Proliferation International History Project (NPIHP) Working Paper #2, Wilson Center, 2012.

[3] Li Jue et al., eds., op. cit., p. 258.

[4] The Ninth Bureau, under the Second Ministry was established in 1958 and responsible for nuclear weapon development and the construction of the Northwest [Qinghai] Nuclear Weapons Research and Manufacturing Based at Qinghai province (often referred to as Base 221). The Beijing Nuclear Weapons Institute (Ninth Institute), also under Ninth Bureau, was established in 1958 to receive and study Soviet data and technology about the atomic bomb. Major nuclear weapon work was conducted there until around 1964, when the Qinghai Base 221 construction was complete. In February 1964, the Ninth Bureau and the Ninth Institute were combined into the Ninth Academy of Nuclear Weapons Research and Design of the Second Ministry. In March 1965, the administration of the Ninth Academy then moved from Beijing to the Qinghai Base 221 (soon to be renamed Plant 221). The Beijing branch of the Ninth Academy was still referred to as the Ninth Institute after 1965.

[5] Liu Xiyao, ed., Witness the birth of China’s first hydrogen bomb, Hunan Jiaoyu Press, Changsha, 2017 (in Chinese), p. 3.

[6] Song Binghuan, Documentary of China's breakthrough in the principle of hydrogen bomb, December 22, 2012, website of Liangdan Yixing (in Chinese).

[7] Liu Xiyao, ed., op. cit., p. 4.

How nuclear fission works Based on Bohr and Wheeler’s liquid drop model

When a positively charged nucleus absorbs a neutron …

… it vibrates …

… stretches …

… and splits.

The fission of the nucleus into two fragments releases a huge amount of energy in the form of excited (“prompt”) neutrons.

These neutrons can be captured by other nuclei and induce more fission events.

By modifying the arrangement and density of the fissile material, fission can proceed as a controlled, self-sustaining reaction or a “runaway” reaction that results in a nuclear explosion.

July 1959
to March 1963

A new institute

Liu then discussed with Qian Sanqiang, then-Deputy Minister of the Second Ministry, the idea of launching a hydrogen bomb program. But because the weaponeers at the Ninth Institute were actively working to develop the first atomic bomb, and to avoid distracting their efforts, Qian agreed to set up a separate research force at the Institute of Atomic Energy (referred to as “Institute 401”) where he was serving as its director.[8] In December 1960, the deputy director of the Institute 401, Peng Huanwu, set up the “group of theory exploration on light nucleus reaction device,” referred to as the “Light Nucleus Theory Group.” In April 1961, Peng himself joined the Ninth Institute as its deputy director before taking the lead of the hydrogen bomb research program in 1963.[9]

In January 1961, Yu Min—a physicist who later would become known as “the father of China’s hydrogen bomb” and a leading figure in China’s overall nuclear weapons development—joined the Light Nucleus Theory Group, which gradually expanded to nearly 40 people. During four years of exploration and research, Yu Min and his group accomplished significant achievements in research on the physical process of the hydrogen bomb and made some preliminary explorations on the bomb’s principle. They also arrived at some preliminary assumptions about the possible overall structure of the bomb. All these research achievements laid essential foundations and would play an important role in the final breakthrough of the hydrogen bomb principle. The group merged with the Ninth Institute in January 1965.

[8] Chen Dan and Ge Nengquan, Biography of Qian Sanqiang, China Youth Press, Beijing, 2017 (in Chinese), p. 169-170.

[9] Wang Xia, Biography of Peng Huanwu, Hebei Shaonian Ertong Press, Shijiazhuang, 2001 (in Chinese), p. 140.

March 1963
to December 1963

Deng Jiaxian (left) known as “the father of China’s atomic bomb” and Yu Min (right) known as “the father of China’s hydrogen bomb,” together. Undated. (Credit: Xie Jianyan / The story of Liangzi website)
Deng Jiaxian (left) known as “the father of China’s atomic bomb” and Yu Min (right) known as “the father of China’s hydrogen bomb,” together. Undated. (Credit: Xie Jianyan / The story of Liangzi website)

A dead end

In March 1963, Deng Jiaxian, director of the theoretical division of the Ninth Institute, submitted the preliminary theoretical design of China’s first atomic bomb. Subsequently, part of his division moved on to explore hydrogen bomb theory. On September 3, 1963, after Marshal Nie Rongzhen examined the progress reports made by the leaders from the Second Ministry and Ninth Institute on the development of the first atomic bomb and plans for nuclear weapons, he declared that “after the detonation of the first atomic bomb, it is essential to quickly arrange the plans of the miniaturization of nuclear devices and the hydrogen bombs.”[10]

Once it had completed the theoretical design of the first atomic bomb, the Ninth Institute reinforced its “hydrogen bomb exploration group,” which was directed by Peng Huanwu.[11] The group started with the Soviet “layer-cake” model.[12] The model, however, was missing some data and Peng had to collect new information to complete it.[13] It is still unknown how Peng obtained the Soviet model, but there are several opportunities through which the design information of the model may have been disclosed—including through the 1957 agreement with Moscow or when Soviet experts helped to design the lithium deuteride production line at Baotou (Plant 212) to fuel the boosted atomic bomb in 1958.

The Soviet Union had tested only one layer-cake design bomb—the RDS-6 device, detonated on August 12, 1953.[14] After about a year studying the layer-cake model, Peng Huanwu and his group concluded that it was technically impossible to use the boosted atomic bomb design as a pathway toward the hydrogen bomb. The reason for this involved the boosted atomic bomb’s declining rate of chain reactions, which limited the increase in yield the device could deliver. To overcome this problem, the team proposed to study technical issues, including strong coupling of uranium and lithium deuteride. By May 1965, the group was now hoping that, by adding more uranium 235 to a devices, they could get a larger yield.[15]

[10] Song Binghuan, op. cit.

[11] Liu Xiyao, ed., op. cit., p. 13.

[12] The “layer-cake” model was like the US “Alarm Clock” scheme that alternated spherical layers of fissionable materials and thermonuclear fuel.

[13] Liu Xiyao, ed., op. cit., p. 13.

[14] John E. Pike, Soviet RDS-6S thermonuclear bomb, GlobalSecurity.org, undated.

[15] Liu Xiyao, ed., op. cit., p. 40.

Boosted “layer-cake” implosion fission bomb design
Based on the first atomic bomb device 596 tested in October 1964

High explosives create shock waves that compress a uranium core until the nuclei split, releasing huge amounts of energy in a process called fission.

January 1964
to October 1964

Starting over

On January 29, 1964, the Central Special Committee[16] reported to Mao Zedong—officially the Chairman of the Chinese Communist Party—and the Party’s Central Committee on the development of the atomic energy industry and the atomic bomb. The committee’s report proposed that “the central task of atomic energy for the Third Five-Year Plan (1966-1970) was to resolve the question of the ‘have or not’ of the nuclear bomb and thermonuclear bombs.”[17]

The development of the H-bomb started over—again.

Between 1964 and 1965, facing pressure from the central government to find a new pathway to the hydrogen bomb, the Ninth Academy (formerly known as the Ninth Institute) hosted discussions and debates on the topic and searched widely in the foreign scientific literature and news reports for any mention of the hydrogen bomb. At one workshop, Zhou Guangzhao, the deputy director of the academy’s theoretical division, brought a pile of magazines to show the participants that many photos of nuclear missiles had the shape of a long cylinder, instead of a large sphere as the layer-cake model suggested. Zhou believed the configurations of the atomic bomb and the hydrogen bomb were very different, and so their associated principles would also be different in nature.[18]

[16] In November 1962, to accelerate the detonation of China’s first atomic bomb, the Central Special Commission was established. It was also dubbed the “Fifteen-Member Special Commission,” with Premier Zhou Enlai as the director of seven vice premiers and seven ministers.

[17] Peng Jichao, The huge eastern bang, Party school of the CPC Central Committee Press, Beijing, 1995 (in Chinese), p. 333.

[18] Wang Xia, op. cit., p. 168.

All the team could find was one sentence from a US newspaper that read: “Edward Teller’s brilliant idea that led to the creation of hydrogen bomb.”

The theoretical division subsequently set up a group to investigate US and Soviet newspapers and scientific papers on the subject. Those from the group went to the Beijing library to borrow all foreign newspapers, including all issues of the New York Times and Pravda since 1945. This effort required special permission from the Second Ministry because foreign newspapers were not available for public use at the time.[19] After loading those materials—reportedly in Jeeps—and bringing them back to the academy, the team started to read through all of them. All the team could find was one sentence from a US newspaper that read: “Edward Teller’s brilliant idea that led to the creation of hydrogen bomb.”[20] But, of course, the paper was not revealing what this “brilliant idea” actually was.

[19] Liu Xiyao, ed., op. cit., p. 23-24.

[20] Liu Xiyao, ed., op. cit., p. 16.

SPOTLIGHT

International reactions to China’s nuclear weapon: ‘A Bomb for all Asians and Africans’
By Nicola Leveringhaus

On the day China tested its first nuclear fission implosion device, the country’s Premier, Zhou Enlai, wrote a letter to foreign capitals, keen to minimise negative international diplomatic fallout to its test. Many in the United States feared a nuclear weapon proliferation cascade in the wake of China’s October 1964 test.

Continue reading →

SPOTLIGHT

International reactions to China’s nuclear weapon: ‘A Bomb for all Asians and Africans’

By Nicola Leveringhaus

On the day China tested its first nuclear fission implosion device, the country’s Premier, Zhou Enlai, wrote a letter to foreign capitals, keen to minimise negative international diplomatic fallout to its test. Many in the United States feared a nuclear weapon proliferation cascade in the wake of China October 1964 test.

Taiwan, Japan, and India indeed openly criticized China’s testing. Beijing’s new nuclear weapon capability was considered a threat, and it likely reinforced demand for a continued US extended security guarantees in the region. Yet outright condemnation was the exception, not the rule. Instead, China’s nuclearization in the 1960s was, in most parts of the world, welcomed as a “bomb for all Asians and Africans.”

China’s nuclear weapons tests of the 1960s (there would be 10 in total) were interpreted by many developing countries as an equaliser, serving the interests of Communist powers and anti-colonial independence movements that had no nuclear deterrent of their own. When Zhou wrote his letter, it was mainly addressed to Asia and Africa, not Europe or the United States. Soon after, on October 30, 1964, another high-ranking Chinese official, Liu Shaoqi, declared that China’s bomb was a bomb that belonged to others. Liu could make this statement with some confidence as Beijing’s test was being welcomed by several states in Eastern Europe, Southeast Asia, the Middle East, and Africa. Declassified archival documents within the Chinese Foreign Ministry show that these countries began to link Beijing’s scientific success to wider national liberation and international racial movements. China’s bomb was the first nuclear weapon to be possessed by a non-white, non-developed country.

The positive foreign state responses were recorded diligently within the Chinese Foreign Ministry. The Yemeni Ambassador Saleh Ali Al-Ashwal described the testing not simply as a victory for China, but also as an effort to safeguard international peace. In Indonesia, the racial element was explicitly pronounced, with a statement that now with China’s bomb, “not only white people can produce nuclear bombs.” In a cable, the Pakistani Foreign Ministry noted that: “Some said that this was the pride and glory of the Asians. Some said that we could talk to the United States on an equal footing now that we have the nuclear bomb and could speak on Pakistan’s behalf.” A message of the Ghanaian Ambassador to Algeria was also received, with the statement that “China’s atomic bomb belongs to all the Asian and African peoples.” In Cuba, the Chinese Embassy noted that Augusto Martinez Sanchez, the Cuban Minister of Labour, and Eulogio Cantillo, the chief of staff of the department of Protocol in the Ministry of Foreign Affairs, apparently verbally congratulated China, with the latter stating: “[T]he Cuban ambassador said that China having atomic bombs is the same as us having atomic bombs”.

This outside validation and celebration of China’s nuclear testing is not well remembered today. Yet it remains ingrained in China’s own recollection of its nuclear past. It reinforces a goal China had with it nuclear weapons program from the start: to be seen as fundamentally different from other nuclear weapons states.

Nicola Leveringhaus is a senior lecturer with the Department of War Studies, King’s College London, United Kingdom. She is the author of China and Global Nuclear Order (Oxford University Press, 2015).

November 1964
to June 1965

A goal code-named “1100”

On November 2, 1964, as they were discussing future nuclear testing issues, Premier Zhou asked his Minister Liu Jie when the hydrogen bomb would be ready. China had successfully conducted its first atomic bomb (device 596) test in October 1964.[21] Liu Jie replied that “the pre-research on the theory of the hydrogen bomb had been explored, and there were still many questions that cannot be fully understood. It will probably take three to five years.” Premier Zhou replied that five years were too many.[22] On January 7, 1965, Liu Jie delivered a speech at the meeting of the Second Ministry, conveying Mao’s new instructions to the audience: “If we have hydrogen bombs and missiles, wars may not be fought, and peace will be more secure. We make the atomic bombs but will not be too many. It will be used to scare [enemies] and embolden [ourselves].” Mao also said that “it still needs three years to have the hydrogen bomb, which is too slow.” [23]

In January 1965, the Second Ministry decided to transfer the Light Nuclear Theory Group of the Institute of Atomic Energy to the theoretical division of the Ninth Academy, as a way to speed up the development of the hydrogen bomb. By merging the two research forces, the ministry hoped to quickly resolve the key problems of hydrogen bomb development.[24] Yu Min was appointed deputy director of the now fleshed-out theoretical division.

On February 3, 1965, the Second Ministry set the goal of testing the first hydrogen bomb device in 1968.[25] When explaining the reasons why the ministry chose this target year, Liu Jie said that it would make China the fastest among the then-nuclear states to develop a hydrogen bomb from the first atomic bomb.[26] At the time, they defined a hydrogen bomb as one that had an explosive yield of more than one million tons of TNT equivalent, with fusion energy providing more than 30 percent of the yield. The next day, the Central Special Committee approved the Second Ministry’s proposal during a meeting presided by Premier Zhou.[27]

[21] China formally codenamed its first nuclear bomb “device 596” to commemorate the date of June 1959 when Moscow sent a letter to Beijing informing that it would not provide the promised atomic bomb model and data.

[22] Liu Jie, Policy makers and organizers of my country's atomic energy cause, People’s Daily website, January 4, 2006.

[23] Song Binghuan, op. cit.

[24] Li Jue et al., eds., p. 276.

[25] Song Binghuan, op. cit.

[26] Liu Jie, op. cit.

[27] Song Binghuan, op. cit.

Mao’s new instructions to the audience: “If we have hydrogen bombs and missiles, wars may not be fought, and peace will be more secure.”

Following this decision, the Ninth Academy held a series of meetings to discuss how to make a breakthrough in understanding the theory of the H-bomb before 1968. Since 1965, Liu Xiyao, the then-deputy minister of the Second Ministry, visited the theoretical division every week to urge and encourage the group’s progress in formulating a specific research plan to create hydrogen bomb technology. He believed the theoretical division was the key for making a breakthrough in the H-bomb concept.[28] The research plan mainly consisted of aiming at the theoretical design of a thermonuclear warhead with a weight of about one metric ton and a power of one megaton, to be tested in 1968.[29] The theoretical design was code-named “1100,” where “1000” referred to its weight in kilograms and “100” referred to its yield in Chinese units of Wan tons. (For large numbers, the Chinese numeral system uses unique names for all powers of 10 starting to the 4th; one Wan is equal to 10,000 and 100 Wan tons are equal to one megaton of TNT equivalent.) The research plan also required the theoretical division to explore principles, materials, configurations, and calculation methods related to a fusion warhead. This first plan showed clearly that the H-bomb would be delivered by missiles and was not to be confused with a boosted atomic bomb dropped by bombers.

From February 1965 onward, the weaponeers tried different routes and proposed different ideas, but none was successful. They first focused on two types of H-bomb models: the non-thermodynamic equilibrium model developed by Yu Min when he was at Institute 401 and the layer-cake model, even though Peng had concluded in 1964 that it could not host a hydrogen bomb. The first model required the ignition of liquid deuterium under non-thermodynamic equilibrium. This was similar to the “classical super” idea,[30] which consisted in using a fission bomb to ignite a mass of deuterium at high temperature.[31] The Monte Carlo simulation group of the theoretical division conducted many probabilistic simulations and proceeded to multiple program iterations, only to conclude that this method could not work because, in every configuration, the energy consumption in the chain reaction was greater than the energy generated. The non-thermodynamic equilibrium model was therefore discarded.[32]

In the first half of 1965, the weapon designers also focused on the calculations of the layer-cake model, which at the time was the most likely to reach a high temperature.[33] Based on calculations of relevant configurations, they found that even when increasing the weight and yield of the device, the fusion-to-fission ratio of the total yield did not increase and was still far from the “1100” goal of one megaton in yield.

[28] Liu Xiyao, Mountain Climbing and Through Fog—The memoir of Liu Xiyao, Wuhan University Press, Wuhan, 2000 (in Chinese), p. 116.

[29] Zheng Shaotang and Zeng Xiancai, Yu Min, Guizhou Renmin Press, Guiyang, 2005 (in Chinese), p. 54.

[30] Zheng Shaotang and Zeng Xiancai, op. cit., p. 50-51. It should be noted that some accounts emphasized Qian Sanqiang, then-director of Institute 401, once met in July 1959 with Klaus Fuchs in East Germany, when Fuchs may have given his thoughts on thermonuclear weapons. Fuchs, who worked at Los Alamos during the Manhattan Project, played an important role in the development of the wartime A-bomb and, in time, the conceptualization of the H-bomb (see, e.g., Thomas Reed and Danny Stillman, ‘The Chinese Nuclear Tests, 1964–1996’, Physics Today, September 2008). The non-thermodynamic equilibrium model idea could have been impacted by Klaus.

[31] See, e.g., John E. Pike, Classical Super / Runaway Super, GlobalSecurity.org, undated.

[32] Liu Xiyao, ed., op. cit., p. 46-47.

[33] Liu Xiyao, ed., op. cit., p. 40.

July 1965
to August 1965

A two-step plan

The first five months of effort since setting the “1100” goal had produced only rejections of proposed models and further evidence of lack of feasibility. Meanwhile, the 1968 deadline to test an “1100” warhead was fast approaching. Leaders of the Ninth Academy subsequently realized they could not reach their target in one step, but only incrementally. In early July 1965, the leadership therefore adjusted its H-bomb research plan by dividing it now into two steps.[34]

RELATED:
International reactions to China’s nuclear weapon: ‘A Bomb for all Asians and Africans’

The first step was to continue exploring the principle of the hydrogen bomb by conducting several tests of a large-yield boosted nuclear bomb. Under the plan, the weight limit would be relaxed and the first designed one-megaton-yield boosted nuclear bomb would be carried by the H-6 bomber. At the time, the H-6 bomber was set to have a maximum payload of eight tons, which meant the “1100” goal was, in effect, relaxed. (The boosted nuclear bomb was still based on the layer-cake model.) Once the yield was be reached, the second step of the revised plan would consist in miniaturizing the device by designing a “1100” hydrogen bomb for missile delivery.[35]

[34] Zheng Shaotang and Zeng Xiancai, op. cit., p. 62.

[35] Liu Xiyao, ed., op. cit., p. 57.

“Our vision is to strive for breakthroughs on the one hand and prepare for repetition on the other.”

On July 10, 1965, the Second Ministry outlined its revised two-step hydrogen bomb research plan in a report submitted to the Central Special Committee.[36] The report proposed a series of “hot” tests to explore the H-bomb principle: The first step would carry out the air-burst test of a boosted atomic bomb in June 1966, to understand the progress of the thermonuclear reaction of lithium deuterium at high temperature. Then, a larger, three-phase, air-dropped bomb—in fact, a larger yield layer-cake device—would be tested in 1967.[37] Referring to what the study of foreign materials had brought, the report also said that “the key breakthroughs in hydrogen bomb technology seems to have started from the test of large-scale three-phase devices. We currently do not have plutonium and tritium. Using the existing nuclear materials and implosion structures, to start a breakthrough with testing the large-scale three-phase devices, we may need to conduct further theoretical research, and the test of [the boosted atomic] bomb 596L.” (China’s boosted atomic bomb was coded 596L, which means it was based on the first atomic bomb device, 596, which received an additional layer of thermonuclear fuel in the form of lithium 6 deuteride, with the letter L standing for lithium.) Finally, the report stated, “our vision is to strive for breakthroughs on the one hand and prepare for repetition on the other.” [38]

[36] Song Binghuan, op. cit.

[37] The so-called “three-phase” nuclear device at the time was a layer-cake-type device, which consisted of three phases: fission, fusion, and then fission again. During the first phase, the highly-enriched uranium or plutonium core generated the fission explosion. The second phase was the fusion reactions of the layer of solid thermonuclear fuel (lithium deuteride) surrounding the core. Tritium was generated when neutrons from the first phase explosion bombard the lithium. Meanwhile, the high temperature generated by the fission explosion caused the fusion reactions of the deuterium and tritium. The third phase was the fission reaction of the layer of uranium 238 (natural uranium or depleted uranium) surrounding the thermonuclear fuel. The very-high energy neutrons released from the fusion reactions can fission uranium 238. For a layer-cake-type model, additional layers of thermonuclear materials and uranium 238 could be used.

[38] Song Binghuan, op. cit.

Boosted atomic bomb (device 596L)
Tested on May 9, 1966

The 596L bomb weighed approximately 5,000 kilograms and was approximately 2 meters in diameter.

It used the boosted “layer-cake” implosion fission bomb design.

The 596L boosted atomic bomb was dropped from an H-6a bomber on May 9, 1966. It produced an air-burst nuclear explosion with a yield of 220 kilotons.

Although the test was successful, it had several limitations. The main one was that the 596L boosted atomic bomb could not create a self-sustaining fusion reaction because of the fast-declining rate of chain reactions.

Because the configuration limited the yield increase, weaponeers concluded that the boosted fission bomb design could not lead to the hydrogen bomb.

July 1965
to August 1965

After the meeting of the Central Special Committee, the Second Ministry asked the theoretical division of the Ninth Academy to submit as soon as possible a theoretical design plan for a nuclear device that had a power as close to one megaton as possible and could be carried by an H-6 aircraft.[39] Given the tight deadline by the Second Ministry, the division leaders decided that one group should continue working on the 596L bomb, which was planned to be tested in June 1966, while two other groups continued trying to make strides in hydrogen bomb development.

After running some calculations, leaders of the theoretical division proposed three specific requirements for the bomb design:[40] When considering the maximum weight load and volume of the H-6 aircraft, they determined that they could add nuclear materials so the weight of high explosive could be extended by about 1.4 times its overall capacity.[41] At the time, a nuclear device with a yield of about 700 kilotons weighed approximately six tons. That meant that, to get a one-megaton device, the new requirement had to be relaxed so that the device weight could reach up to eight tons, have a yield of one megaton, and reach a certain level of fusion ratio of the total yield. Assuming that the H-bomb would have a fusion-to-fission ratio of about 30 percent and that this three-phase bomb was in fact a layer-cake type bomb, the weaponeers concluded that the required fusion rate could be around 20 percent.

[39] Liu Xiyao, ed., op. cit., p. 36.

[40] The Editing Committee, Essay collection for academician Yu Min’s 80th birthday celebration, Atomic Energy Press, Beijing, 2006 (in Chinese), p. 137.

[41] Liu Xiyao, ed., op. cit., p. 57.

The “hundred-day battle”

Yu Min confers with other scientists in an undated photo. (via ESSRA)
Yu Min confers with other scientists in an undated photo. (via ESSRA)

September 1965

Gathering in Shanghai

In late September 1965, Yu Min and over 50 researchers gathered in Shanghai for what may have been the most intense period in the development of the hydrogen bomb. The calculators and programmers present immediately installed various computer programs brought from Beijing and carried out debugging and calculations of these programs necessary to test the bomb principle. The group first resolved a problem involving non-conservation of neutrons in the program calculations. Meanwhile, a group of mathematicians worked day and night to quickly compile a large-scale computer program, to start the optimal design of the three-phase hydrogen aerial bomb, and to carry out many numerical simulations.[42] Because of the poor stability of computers at that time, the physicists had to verify each calculation by hand to solve problems in time.

For nearly 100 days—and nights—all the physicists, mathematicians, and research assistants gathered in Shanghai would arrange shifts and take turns in the computer room around the clock to solve problems.[43] Those staying in the office were busy drawing, registering, analyzing, discussing, and preparing the next batch of models to be calculated. As Cai Shaohui, a group leader, recalled: “Inspired by a strong sense of mission, everyone was enthusiastic and energetic, and soon calculated a batch of models. Judging from the results, they were not far from the requirements for a successful experiment. As soon as a little precious material is added, the power can be increased to one million tons.”[44] It was reported that the group could design a device of 830 kilotons,[45] however, that its weight was still up to eight metric tons. If they added several kilograms of plutonium, the yield could be increased up to one megaton. But the plutonium would not be available until 1968, the year the “1100” hydrogen bomb was supposed to be tested. In fact, the group still had a long way to go before it could test a one-megaton, three-phase air-dropped bomb by 1967, as promised by the Second Ministry to the Central Special Committee. At that stage, all they could do is create a nuclear device with a yield of up to 700 kilotons, which the committee approved.

[42] Zheng Shaotang and Zeng Xiancai, Yu Min, op. cit., p. 63.

[43] The Editing Committee, 2006, op. cit., p. 158-159.

[44] Cai Shaohui, Remember the passionate moments in my heart, Physics (Chinese magazine), 2006, vol. 35, no. 9, p. 755.

[45] Liu Xiyao, ed., op. cit., p. 78.

These early models all had a very low fusion energy ratio relative to the total yield, which suggested that the thermonuclear material (hydrogen) loaded in the device could not be fully consumed. Yu Min, however, was not surprised by these results.[46] He had explored the boosted atomic bomb model when he was at the Institute 401. At that time, he had found that, although fusion materials can play a role in enhancing the device’s overall explosive power, enhancement alone would not be sufficient without the complete combustion of the fusion material.

[46] Cai Shaohui, op. cit., p. 755.

September 1965

Yu Min in an undated picture. While in Shanghai, Yu would often stay in the computer room to check himself the numerical simulation results printed on tape rolls by the computers. (Photo: CCTV)
Yu Min in an undated picture. While in Shanghai, Yu would often stay in the computer room to check himself the numerical simulation results printed on tape rolls by the computers. (Photo: CCTV)

In Shanghai, the division leaders had hoped Yu Min would lead the group to study how to apply the boosted principle to the real atomic bomb and complete the task of optimizing the design of the enhanced device. Yu spent many days and nights in the computer room immersing himself in the output tape rolls printed by the computers and carefully analyzing the numerical simulation results to search for errors. He selected three numerical computational models and conducted in-depth and detailed systematic analysis to test his computations. But, although the division leaders had assigned him to lead the group to design the larger boosted device of one megaton, Yu Min believed that, to achieve a breakthrough, the fundamental problem was to find the general solution to the hydrogen bomb principle. Since arriving in Shanghai, Yu Min was thinking about this problem in these terms.[47]

[47] The Editing Committee, 2006, op. cit., p. 159-161.

Most of the younger scientists in the group lacked practical experience in scientific research to tackle hydrogen bomb theory.

The younger scientists in the group, however, had been involved only recently in the hydrogen bomb exploration, and most lacked the basic knowledge of hydrogen bombs and practical experience in scientific research to tackle hydrogen bomb theory. To improve their theoretical understanding of the subject matter, Yu Min held a series of lectures on the boosted nuclear bomb during two weeks in Shanghai. As it turns out, it was during his lectures that Yu Min found the answer to their problem: The production rate of tritium from neutron activation in the boosted model was too slow.

Yu Min further explained that, because the neutron-tritium cycle process in the boosted model cannot catch up with the speed of the bomb body’s disintegration process, the energy release rate in the fireball could not equal the energy loss rate—which was several times higher. Under such a huge deficit, the fireball’s temperature was unable to create a self-sustaining fusion reaction. Yu Min said that the solution to this problem was to “either try to slow down the fireball propagation speed or increase the energy release rate.”[48]

[48] Cai Shaohui, op. cit., p. 756.

A mistake and a discovery

One day, as the Shanghai group proceeded with computer simulations, Liu Yuqin, a programmer with the group, suddenly got the surprising result of a three-megaton yield—to which the entire computer room ran full of excitement and shouted they had “found a new world.” After hearing the news, Yu Min, Cai Shaohui, and physics team leader Meng Zhaoli rushed into the room to find out about this result. Unfortunately, after careful check, they found Liu had made a mistake in entering the mass of the thermonuclear fuel into the program.[49] This error, however, would provide an important clue to the group as to what direction to pursue. As Meng Zhaoli recalled, “We mistakenly increased the light nucleus material by 20 times and made us see the physical picture of a three-megaton H-bomb,” adding that “it clearly showed that the most important factor to realize an explosion of the H-bomb is to increase the density of the light nucleus material.”[50]

Researcher Zhang Suochun also recalled the moment: “After analysis on the reason for the discovery of the so-called ‘New World,’ it turned out that Liu, who was responsible for the preparation of the calculation model data, filled in the wrong physical parameters, resulting in unrealistic calculation results. But this mistake reminded the researchers that one of the most important factors in obtaining a high-yield hydrogen bomb is to increase the density of light nuclear materials, and that the design of hydrogen bombs should take the road of high density.”[51]

[49] Liu Xiyao, ed., op. cit., p. 67.

[50] The Editing Committee, 2006, op. cit., p. 136-137.

[51] Liu Xiyao, ed., op. cit., p. 67.

“Yu Min said, ‘Let's look at two models, one is ideal and the other is closer to reality.’”

Yu Min subsequently narrowed his focus on the key question of increasing the density of light nuclear materials in the bomb design.[52] To achieve a high degree of compression, improving the energy-utilization rate of explosives alone would not suffice. Yu Min believed the key was to use the energy released by the atomic bomb to increase the density of the hydrogen before it is consumed in the fusion reaction.

Previously, researchers had hoped the detonation of the atomic bomb would create the high temperature and high-density conditions necessary for self-sustaining the fusion reaction. But this principle was not applicable to the boosted layer-cake model, in which many physical phenomena were triggered by the atomic bomb explosion, with both positive and destructive effects on the desired conditions of pressure and temperature.

[52] The Editing Committee, 2006, op. cit., p. 160.

Yu Min's breakthrough

The challenge now seemed to be about how to discern the materials with suitable properties and the configurations that can promote the physical factors having a positive role on the reaction, while, at the same time, inhibiting those other physical factors having a destructive role. Yu Min had to go into deep thinking again. As Cai recalled: “On Friday, October 29, I and Yu Min took a walk on a nearby field trail after dinner. When we talked about how to create conditions for the full combustion of thermonuclear materials, Yu Min pointed out bluntly that the boosted model’s configuration is not conducive to the compression and combustion of thermonuclear materials. He gave me his views in great detail, and I was attracted to his fresh thinking and irrefutable arguments. I said, ‘Let's do it right away, shall we?’ Yu Min said, ‘Let's look at two models; one is ideal, and the other is closer to reality.’”[53]

Yu Min subsequently analyzed the various forms of energy being released from the atomic bomb explosion and compared their characteristics and their proportions in the total energy. This work helped him clarify one of the energy forms to be used and to propose a sophisticated structure to reduce this energy loss and improve its consumption rate. He made estimates, including how much energy would be necessary to compress lithium deuterium, to what degree lithium deuterium could be compressed, and how to ignite and maintain the burning, self-sustaining reaction.

Yu Min’s idea was first to verify whether the compression of the energy of the atomic bomb could make the fusion material burn self-sustainably. To achieve this, they used two models with which they simulated part of atomic bomb energy to instantly act on the “secondary” through a mechanism on the first model and took it as the outer boundary conditions of the second calculation model.

[53] Cai Shaohui, op. cit., p. 756.

[54] Liu Xiyao, ed., op. cit., p. 73-78.

The group in Shanghai believed Yu Min finally had “held the bull by the nose” by achieving a breakthrough in the staged H-bomb principle.

On the evening of November 1st, the group started running the program to calculate Yu Min’s new model on the J501 computer. The result was just as Yu Min expected. In excitement, they temporarily added a model with a different material ratio, and the result was fine. The next day, another model's calculations also yielded perfect results. The simulation results of two types of three models showed that, as long as they could control the energy of the atomic bomb, designing a one-megaton hydrogen bomb was now feasible.

On November 5, Yu Min briefed the group about the calculation results and the concept of the new hydrogen bomb. He demonstrated the energy transfer of the atomic bomb and the configuration of the primary (fission bomb) and the secondary (light nuclear materials) in the hydrogen bomb. Yu Min's bold assumptions and solid theoretical knowledge convinced everyone. The group in Shanghai believed Yu Min finally had “held the bull by the nose” by achieving a breakthrough in the staged H-bomb principle. After the briefing, the group leaders determined to establish a team on the “new principle of the H-bomb” to work with Yu Min on further improving the new principle. The others would continue optimizing the design of the larger boosted device as their assigned task—and would hurry to complete it. The “new principle” team immediately began compiling the programs for the new H-bomb principle work. On November 14, the new program was ready.

To test if the special configuration used in the new principle of the hydrogen bomb was in sufficient accordance with the theory, Yu Min asked the Monte Carlo simulation team to develop a numerical simulation program dedicated to this problem. The team completed the computer program within a week—a much quicker turn around compared to the one to two months it would normally take. Three full days of calculations later, the numerical simulation results showed Yu Min a specific scheme of the configuration and confirmed that using the atomic bomb to trigger the secondary is feasible.[54]

Meanwhile, the “new principle” group continued its extensive work under the direction of Yu Min and discovered a number of important physical phenomena and laws. Yu Min summed up the research results into a basic complete hydrogen bomb physics scheme, including the principle of energy transmission from the primary to the secondary material and configuration.

In late November, upon learning the news on Yu Min’s breakthrough in the hydrogen bomb principle, Ninth Academy’s theoretical division director Deng Jiaxian immediately flew to Shanghai. Deng and Yu discussed in detail the new principle and analyzed the calculation results, which convinced Deng to approve it.

In early December, Yu Min was asked to come back to Beijing to report his new findings, while the other members of the “new principle” team would stay in Shanghai to study the new scheme in depth and improve their calculations. The group in Shanghai also continued the optimization design work of the boosted three-phase hydrogen aerial bomb.

Finally, in early January 1966, the researchers returned to Beijing with the new hydrogen bomb principle they had sought so hard for nearly 100 days and nights in Shanghai.

Testing the Bomb

Chinese soldiers prepare to watch the hydrogen bomb test on June 17, 1967.
Chinese soldiers prepare to watch the hydrogen bomb test on June 17, 1967.

September 1965

On December 9-10, 1965, the Ninth Academy held its next two-year plan meeting for 1966-67 on nuclear weapons research and production at its Qinghai nuclear weapon research and manufacturing base (Plant 221).[55] At the meeting, Yu Min introduced in detail the theoretical scheme of the two-stage hydrogen bomb principle that uses the atomic bomb as the primary to trigger the secondary, as well as the key technical and structural problems that had to be solved to realize that scheme. He also put forward preliminary requirements, including for the detonation experiments, device processing and manufacturing, and nuclear testing and post-testing analysis. Most participants agreed with Yu Min’s proposed new H-bomb principle. They believed it was now possible to achieve the development of a one-megaton-class hydrogen bomb with a relatively small volume, light weight, and high fusion ratio by late 1967 to early 1968.

At the meeting, Deputy Minister Liu Xiyao decided on a new policy for achieving a breakthrough on the hydrogen bomb, taking the new scheme as the main goal.[56] The new scheme would serve as the first option and main direction to develop the missile thermonuclear warhead. Liu also decided to complete the research and testing of the boosted three-phase bomb as a backup strategy. Later, Yu Min commented that, in retrospect, Liu’s swift decision prevented the development program from being delayed by the Great Cultural Revolution, which broke only a few months later and lasted a decade. Had Liu Xiyao thought twice, the H-bomb breakthrough may have never materialized.[57]

A new two-year plan included preparations for three nuclear tests that aimed for a breakthrough in confirming the H-bomb principle. First, they would conduct the test of the layer-cake model 596L around June 1966, as was already scheduled, to verify if the theoretical calculations of the performance of thermonuclear materials based on data from the foreign literature were in line with observations. The second test would consist in exploding a reduced-yield, two-stage hydrogen bomb at a tower in late 1966 to confirm the principle of the hydrogen bomb. The third and last test would then proceed with an air-burst detonation of a full-yield, three-megaton H-bomb at the end of 1967 or beginning of 1968—hopefully achieving the breakthrough about half-a-year earlier than originally planned. In addition, the plan included a backup test of a one-megaton, boosted three-phase aerial atomic bomb in case the reduced-yield test failed. These three tests are often referred to as “the trilogy of H-bomb development in China.”[58]

[55] Zheng Shaotang and Zeng Xiancai, op. cit., p. 71.

[56] Zheng Shaotang and Zeng Xiancai, op. cit., p. 71.

[57] Peng Jichao, The Huge Eastern Bang, Party school of the CPC Central Committee Press, Beijing, 1995 (in Chinese), p. 335.

[58] Liu Xiyao, Mountain Climbing and Through Fog—The memoir of Liu Xiyao, Wuhan University Press, Wuhan, 2000 (in Chinese), p. 117.

September 1965

First test: Boosted atomic bomb (device 596L)

The first test of the “trilogy” was conducted without problem and even ahead of schedule. On May 9, 1966, the boosted atomic bomb 596L was dropped from the H-6a aircraft; it exploded over the Lop Nor test site, a former salt lake located in now arid northwestern China. The yield of the test bomb was estimated at 220 kilotons and the test was coded operation 21-72.[59]

[59] Xue Jianyuan, The Ninth Bureau of the Second Ministry: Ten years from its establishment to its demise, The Story of Liangzi, June 7, 2017.

Second test: Low-yield hydrogen bomb (device 629)

The second test in the series, however, proved more challenging. To conduct the H-bomb principle test by late 1966, the Ninth Academy had first to tackle key problems in theory, experiment, design, processing, and manufacturing.[60] Immediately after the two-year plan was released, in January 1966, the experimental division started a series of detonation experiments to finalize the physical parameters of the “primary.” The basic principle of ​​the hydrogen bomb proposed by Yu Min was to transmit the controllable energy generated by the atomic bomb to the secondary through a well-defined structure called “energy transport system.” The most critical challenge, therefore, was to design the primary so it would not accidentally detonate when introducing the energy transport system into the device. The design also had to ensure that this system would remain undamaged during the energy transport process after detonation. Three nearly-insurmountable, yet unspecified in available sources, technical problems had initially been identified in the “trigger” structure scheme proposed by the theoretical division for detonation experiment simulation, on which Yu Min and his researchers would spend significant time and effort as they sought solutions.

After more than three months of unremitting efforts, hundreds of detonation experiment simulations, and repeated research and analysis, the structural configuration of the “trigger” system was finally solved. On April 7, the theoretical division revised the original theoretical model based on the results of the simulations. The theoretical design model of the hydrogen bomb principle test device code-named 629 was born.[61] Despite progress in the theoretical calculations and detonation simulation experiments, however, the design work for the device 629—the second step of the “trilogy”—was behind schedule as the “Great Cultural Revolution” quickly spread nationwide after May 16, 1966. It was not until November 1966 that the final test plan of the primary and secondary were both determined. Unlike the US early H-bomb design, China’s contained two balls, one for the primary (or “trigger”) and another for the “triggered” secondary.[62]

[60] Zheng Shaotang and Zeng Xiancai, op. cit., p. 73.

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[61] Zheng Shaotang and Zeng Xiancai, op. cit., p. 73. There are different interpretations about why the Chinese chose this code-name. Unlike the “596” atomic bomb, the hydrogen bomb principle test had no official statement about its code-name 629. One former weaponeer reported that it was from “639,” the month and year when Mashal Nie instructed the Ninth Institute to work on the H-bomb in September 1963 [see, e.g., Li Zhiju, China’s Nuclear Shield, Culture and Art Press, Beijing, 2006 (in Chinese), p. 100]. The weaponeers addressed that the “639” was for the full-yield H-bomb tested in 1967, and its principle test device was reportedly code-named “629” because it was for a reduced-yield test, therefore was given a “reduced” code number. However, another weaponeer involved in the numerical simulations of both “629” and “639” H-bombs designs mentioned that the code-name 629 was not from the date, but rather was related to the device’s configuration [see, e.g., Liu Xiyao, ed., op. cit., p. 284].

[62] Xue Jianyuan, op. cit.

A large canister containing device 629 is moved to the 102-meter-tall tower on December 26, 1966. (Credit: Xie Jianyan / The story of Liangzi website)
A large canister containing device 629 is moved to the 102-meter-tall tower on December 26, 1966. (Credit: Xie Jianyan / The story of Liangzi website)
The tower erected for the 629 device test at the Lop Nur test site in northwestern China, photographed by a US reconaissance satellite on December 8, 1966. The test occurred on December 28, 1966. (via National Security Archive)

The device 629’s primary was similar to that of the first atomic bomb device 596 tested in 1964, which had a solid uranium 235 core with a uranium deuteride neutron source and no thermonuclear materials.[63] The device 596’s yield was set to be about 20 kilotons,[64] whereas the device 629’s design yield was about 100 kilotons. This limited total yield required the secondary to host less thermonuclear materials and use lead metal to replace the natural uranium.[65]

The configuration of the H-bomb device was much more complicated than that of the first atomic bomb device. Some parts had unusual shapes that made the engineering design and manufacturing difficult, further complicated by the delay generated by the theoretical design plan. On December 18, 1966, through once again unremitting efforts, the weaponeers completed the production of one 629-1 device that was ready for the “hot” test.[66]

[63] Liu Xiyao, ed., op. cit., p. 207.

[64] Liu Xiyao, ed., op. cit., p. 244.

[65] Zheng Shaotang and Zeng Xiancai, op. cit., p. 73.

[66] Liu Xiyao, ed., op. cit., p. 225-226.

Low-yield hydrogen bomb (device 629)
Tested on December 28, 1966

The 629 nuclear device inside the container weighed approximately 1,500 kilograms and was approximately 3 meters high and 1.5 meters in diameter.

The bomb used a two-stage design in a “primary and secondary” configuration.

The primary consisted of a pure fission bomb design.

The secondary was made of light thermonuclear material and was designed to limit the explosive yield.

During the explosion, the primary would first detonate to create high-temperature and high-pressure conditions.

The extreme energy would then be transferred to the secondary triggering self-sustaining fusion reactions of the thermonuclear material.

The 629 hydrogen bomb exploded from atop a 102-meter-tall steel tower on December 28, 1966. It produced a surface-burst nuclear explosion with a yield of 122 kilotons.

Although the bomb had a limited yield, it proved that China’s hydrogen bomb principle was working.

The next step would consist in minimizing the H-bomb’s payload and volume so it could fit in the H-6 bomber while increasing the yield.

The reduced-yield, two-stage hydrogen bomb device known as 629 was to be exploded atop of the backup tower of the first 596 atomic bomb test to obtain more precise measurements of the H-bomb yield and reduce the overall cost. In addition, to minimize the contamination from such a low burst position, the yield of device 629 had to be reduced.[67] There were concerns that such a reduced, yet still large, yield explosion at a low altitude would result in widespread ground radiation contamination. To address this problem, the leaders of the nuclear test site proposed to solidify the ground surrounding the tower by paving a 50-meter radius circle with a 20-centimeter-thick layer of crushed stones covered with a 10-centimeter-thick concrete layer.[68] In addition, they proposed to pave an additional ring up to 230 meters in radius with a 10-centimeter-thick layer of crushed stones. With these measures, they hoped to reduce the radiation fallout by about two thirds.[69]

[67] Du Xiangwan, In memory of nuclear physicst—Wang Ganchang, Atomic Energy Press, Beijing, 2010 (in Chinese), p. 403.

[68] Xiong Xuelin, Cheng Kaijia, Guofang Keji University Press, Changsha, 2003 (in Chinese), p. 207-209.

[69] Cheng Junze and Long Shouzhan, ed., “Zero Time” explosion—memories of Lop Nor, Zhongshan University Press, Guangzhou, 2011 (in Chinese), p. 289.

The site of the second tower used for the 1966 test of device 629 of the H-bomb principle (coordinates: 40°47'56.14"N/ 89°49'18.01"E). The shadows of the 50-meter and 230-meter radius circles remain visible. (Satellite imagery: Esri, Maxar, Earthstar Geographics, and the GIS User Community)
The site of the second tower used for the 1966 test of device 629 of the H-bomb principle (coordinates: 40°47'56.14"N/ 89°49'18.01"E). The shadows of the 50-meter and 230-meter radius circles remain visible. (Satellite imagery: Esri, Maxar, Earthstar Geographics, and the GIS User Community)

On December 28, 1966, the hydrogen bomb device 629-1 successfully exploded.[70] Supervised by Marshal Nie Rongzhen, the test was coded operation 21-42.[71] The yield of the explosion was measured at 122 kilotons,[72] which was larger than the calculated theoretical value.[73] The weight of device 629 may have been approximately 1500 kg.[74]

The mushroom-shaped smoke cloud formed by China’s hydrogen bomb principle test (device 629) on December 28, 1966. (Credit: Xie Jianyan / The story of Liangzi website)
The mushroom-shaped smoke cloud formed by China’s hydrogen bomb principle test (device 629) on December 28, 1966. (Credit: Xie Jianyan / The story of Liangzi website)

[70] Western scholars and media still often attribute June 17, 1967 (the date of the full-yield H-bomb test) as being China’s first hydrogen bomb test. But many Chinese nuclear experts contend that the test of December 28, 1966, is in fact when China first tested its H-bomb. Although the device 629 exhibited a lower yield, it had all three elements of the hydrogen bomb—principle, material, and configuration.

[71] Xue Jianyuan, op. cit.

[72] Xie Guang, ed., China Today: Defense Science and Technology, National Defense Industry Press, Beijing, 1993 (in Chinese), vol. 1, p. 257.

[73] The Editing Committee, Essay collection for academician Chen Nengkuan’s 80th birthday celebration, Atomic Energy Press, Beijing, 2003 (in Chinese), p. 60.

[74] According to the witnesses, device 629 was placed into a large insulation tank and its total weight (including the device 629, the tank, and the bracket holding the device) was just over two tons [Liu Xiyao, ed., op. cit., p. 189 and 191]. In addition, the tank was taller (approximately 1.3 times higher) than that of the 596 tank with the same diameter. It was reported that the total weight (including the device 596, the tank, and the bracket) was about 1,500 kilograms with the device 596 itself weighing over 900 kilograms [see, e.g., Fang Zhengzhi et.al., Witness the detonation of China’s atomic bomb, Hunan Jiaoyu Press, Changsha, 2014 (in Chinese), p.151]. This suggests that the total weight of the tank and bracket for device 596 may have been over 500 kilograms. Given the weight of the tank for device 629 would be even heavier than that of device 596, the weight of device 629 itself may have been around 1,500 kilograms.

Third test: Full-yield hydrogen bomb (device 639)

On December 30-31, 1966, following the successful test of the hydrogen bomb principle, Marshal Nie held a meeting at the Lop Nor test site to discuss the mission to accomplish the last step of the “trilogy”: the full-yield hydrogen bomb air-burst test (code-named device 639).[75] The program leaders decided the device 639 would take the same principle and configuration as the successfully tested 629 low-yield device and use as much of the leftover parts already made for the three-phase boosted aerial bomb (the so-called “backup” device 658), including its body shell. The program 658 had been the second-hand option for exploration of the H-bomb principle. But now, with the success of the first route, that backup option could be dismantled. The device 639 bomb would be a full-yield, one-megaton-class hydrogen bomb. The test was set to happen on October 1, 1967.

[75] Xie Guang, ed., op. cit., p. 258.

Marshal Nie Rongzhen (left), Zhang Zhenhuan (center), and Qian Xuesen (right) arriving at a meeting to discuss the full-yield hydrogen bomb air-burst test device 639 at the Lop Nor nuclear test site on December 30, 1966. (Credit: Chen Shuyuan / The story of Liangzi website)
Marshal Nie Rongzhen (left), Zhang Zhenhuan (center), and Qian Xuesen (right) arriving at a meeting to discuss the full-yield hydrogen bomb air-burst test device 639 at the Lop Nor nuclear test site on December 30, 1966. (Credit: Chen Shuyuan / The story of Liangzi website)

In January 1967, however, Peng Huanwu, the then-Deputy Director of the Ninth Academy, speculated that the French would conduct its first H-bomb test in 1967, ahead of its initial schedule in 1968.[76] The news pushed the weaponeers to advance the test date from October 1 to July 1, so that their H-bomb detonation could happen before that of the French. From this moment onward, “being ahead of France” had become a slogan that brought everyone’s full dedication to the H-bomb design amid the rising storm of the cultural revolution. The goal of beating France lessened the dissonance that had started to emerge within the theoretical division of the Ninth Academy, with everyone now focused on building and testing the H-bomb as soon as possible.[77]

The theoretical design of the device 639 was relatively straightforward, as mainly based on that of the low-yield device 629. The primary would use the same design as the device 629, whereas the secondary only needed a few modifications from the 629, such as adding more lithium deuteride materials to have a full yield and replacing the lead metal with natural uranium. The design yield ranged from one-and-a-half to three megatons.[78] By February, the weapon designers had completed the basic theoretical design of the hydrogen bomb 639 and, by May, the design was finalized and ready to be manufactured.[79]

[76] Xi Quxing, A Biography of Zhu Guangya, China Youth Press, Beijing, 2017 (in Chinese), p. 259.

[77] Zheng Shaotang and Zeng Xiancai, op. cit., p. 81.

[78] Liu Xiyao, ed., op. cit., p. 305.

[79] Liu Xiyao, ed., op. cit., p. 286.

Full-yield hydrogen bomb (device 639)
Tested on June 17, 1967

The 639 hydrogen bomb weighed approximately 6,000 kilograms with a main body (excluding the tail) of approximately 3.5 meters long and 2 meters in diameter.

The full-yield hydrogen bomb consisted of increasing the density of light thermonuclear fuel to boost the fusion-to-fission rate by producing large amounts of high-energy neutrons.

How the H-bomb 639 works

1. Detonation of fission in the primary
Fission of uranium 235 in the primary generates huge heat, X-rays, and neutrons. The X-rays are transferred to the secondary through the “radiation channel.”

2. Ignition of fusion in the secondary
Temperature and pressure start to build up on the lithium 6 deuteride thermonuclear fuel of the secondary. Meanwhile, fission neutrons generated in the primary enter the secondary and combine with lithium 6 to create tritium.

Deuterium and tritium start to fuse under extreme temperature and pressure in a fusion reaction, releasing large amounts of energy and further fast neutrons.

3. Runaway fission-fusion in the secondary
The excess fast neutrons also bombard the surrounding natural uranium 238, releasing more fission energy that enhances the fusion-fission process and causes a thermonuclear explosion.

The 639 hydrogen bomb was dropped from an H-6a bomber on June 17, 1967. It produced an air-burst nuclear explosion with a yield of 3.3 megatons.

The successful test marked the end of “the trilogy” of China’s H-bomb development, less than three years after its first atomic bomb test.

On June 5, the processing and manufacturing of the first device 639 was complete.[80] Following the two-year plan, Plant 221 in the Qinghai province prepared a total of eight test bombs: four counterweight bombs for the Air Force airdrop training, two telemetry bombs for comprehensive rehearsal at the nuclear test site, and two hydrogen bombs, one of which remained in storage at Plant 221 as a backup. On June 8, the key components and parts of device 639 were shipped from Qinghai to the Malan airport near the test site, where they would be assembled.

On June 17, 1967, China successfully conducted its first hydrogen bomb (device 639) air-burst test, which was coded operation 21-73. The bomb was dropped from a Hong-6A bomber over the air-burst center of the Lop Nor test site (Base 21). The bomb’s descent was slowed by a parachute. Based on post-test analysis of various measurements, including radiochemical analysis of air samples, the explosive power of the hydrogen bomb 639 was estimated at 3.3 megatons. The measured explosion height was 2,930 meters, and ground zero of the explosion was 64.8 meters away from the air-burst center, which corresponds to the target point on the ground.[81]

[80] Liu Xiyao, ed., op. cit., p. 327.

[81] Song Binghuan, op. cit.

By successfully air-dropping a hydrogen bomb in June 1967, China completed its trilogy of H-bomb development, which had been preceded by the boosted atomic bomb test in May 1966 and the H-bomb principle test in December 1966. With the success of test bomb 639, China achieved the development of the hydrogen bomb in a record-breaking period of less than three years since its first atomic bomb test—without foreign help.[82]

[82] The Editing Committee, Essay collection for academician Zhu Guangya’s 80th birthday celebration, Atomic Energy Press, Beijing, 2004 (in Chinese), p. 30.

Hui Zhang

Hui Zhang is a physicist and a senior research associate at the Project on Managing the Atom in the Belfer Center for Science and International Affairs at Harvard University’s John F. Kennedy School of Government, where he leads a research initiative on China’s nuclear policies.

Keywords: China, boosted atomic bomb, h-bomb, hydrogen bomb, nuclear weapons, thermonuclear bomb
Topics: Investigative Reporting, Nuclear Weapons

Notes

[1] China’s official nuclear history is Li Jue, Lei Rongtian, Li Yi, and Li Yingxiang, eds., China Today: Nuclear Industry, China Social Science Press, Beijing, 1987 (in Chinese), p. 13-14.

[2] Shen Zhihua and Yafeng Xia, Between Aid and Restriction: Changing Soviet Policies toward China’s Nuclear Weapons Program: 1954-1960, Nuclear Proliferation International History Project (NPIHP) Working Paper #2, Wilson Center, 2012.

[3] Li Jue et al., eds., op. cit., p. 258.

[4] The Ninth Bureau, under the Second Ministry was established in 1958 and responsible for nuclear weapon development and the construction of the Northwest [Qinghai] Nuclear Weapons Research and Manufacturing Based at Qinghai province (often referred to as Base 221). The Beijing Nuclear Weapons Institute (Ninth Institute), also under Ninth Bureau, was established in 1958 to receive and study Soviet data and technology about the atomic bomb. Major nuclear weapon work was conducted there until around 1964, when the Qinghai Base 221 construction was complete. In February 1964, the Ninth Bureau and the Ninth Institute were combined into the Ninth Academy of Nuclear Weapons Research and Design of the Second Ministry. In March 1965, the administration of the Ninth Academy then moved from Beijing to the Qinghai Base 221 (soon to be renamed Plant 221). The Beijing branch of the Ninth Academy was still referred to as the Ninth Institute after 1965.

[5] Liu Xiyao, ed., Witness the birth of China’s first hydrogen bomb, Hunan Jiaoyu Press, Changsha, 2017 (in Chinese), p. 3.

[6] Song Binghuan, Documentary of China's breakthrough in the principle of hydrogen bomb, December 22, 2012, website of Liangdan Yixing (in Chinese).

[7] Liu Xiyao, ed., op. cit., p. 4.

[8] Chen Dan and Ge Nengquan, Biography of Qian Sanqiang, China Youth Press, Beijing, 2017 (in Chinese), p. 169-170.

[9] Wang Xia, Biography of Peng Huanwu, Hebei Shaonian Ertong Press, Shijiazhuang, 2001 (in Chinese), p. 140.

[10] Song Binghuan, op. cit.

[11] Liu Xiyao, ed., op. cit., p. 13.

[12] The “layer-cake” model was like the US “Alarm Clock” scheme that alternated spherical layers of fissionable materials and thermonuclear fuel.

[13] Liu Xiyao, ed., op. cit., p. 13.

[14] John E. Pike, Soviet RDS-6S thermonuclear bomb, GlobalSecurity.org, undated.

[15] Liu Xiyao, ed., op. cit., p. 40.

[16] In November 1962, to accelerate the detonation of China’s first atomic bomb, the Central Special Commission was established. It was also dubbed the “Fifteen-Member Special Commission,” with Premier Zhou Enlai as the director of seven vice premiers and seven ministers.

[17] Peng Jichao, The huge eastern bang, Party school of the CPC Central Committee Press, Beijing, 1995 (in Chinese), p. 333.

[18] Wang Xia, op. cit., p. 168.

[19] Liu Xiyao, ed., op. cit., p. 23-24.

[20] Liu Xiyao, ed., op. cit., p. 16.

[21] China formally codenamed its first nuclear bomb “device 596” to commemorate the date of June 1959 when Moscow sent a letter to Beijing informing that it would not provide the promised atomic bomb model and data.

[22] Liu Jie, Policy makers and organizers of my country's atomic energy cause, People’s Daily website, January 4, 2006.

[23] Song Binghuan, op. cit.

[24] Li Jue et al., eds., p. 276.

[25] Song Binghuan, op. cit.

[26] Liu Jie, op. cit.

[27] Song Binghuan, op. cit.

[28] Liu Xiyao, Mountain Climbing and Through Fog—The memoir of Liu Xiyao, Wuhan University Press, Wuhan, 2000 (in Chinese), p. 116.

[29] Zheng Shaotang and Zeng Xiancai, Yu Min, Guizhou Renmin Press, Guiyang, 2005 (in Chinese), p. 54.

[30] Zheng Shaotang and Zeng Xiancai, op. cit., p. 50-51. It should be noted that some accounts emphasized Qian Sanqiang, then-director of Institute 401, once met in July 1959 with Klaus Fuchs in East Germany, when Fuchs may have given his thoughts on thermonuclear weapons. Fuchs, who worked at Los Alamos during the Manhattan Project, played an important role in the development of the wartime A-bomb and, in time, the conceptualization of the H-bomb (see, e.g., Thomas Reed and Danny Stillman, ‘The Chinese Nuclear Tests, 1964–1996’, Physics Today, September 2008). The non-thermodynamic equilibrium model idea could have been impacted by Klaus.

[31] See, e.g., John E. Pike, Classical Super / Runaway Super, GlobalSecurity.org, undated.

[32] Liu Xiyao, ed., op. cit., p. 46-47.

[33] Liu Xiyao, ed., op. cit., p. 40.

[34] Zheng Shaotang and Zeng Xiancai, op. cit., p. 62.

[35] Liu Xiyao, ed., op. cit., p. 57.

[36] Song Binghuan, op. cit.

[37] The so-called “three-phase” nuclear device at the time was a layer-cake-type device, which consisted of three phases: fission, fusion, and then fission again. During the first phase, the highly-enriched uranium or plutonium core generated the fission explosion. The second phase was the fusion reactions of the layer of solid thermonuclear fuel (lithium deuteride) surrounding the core. Tritium was generated when neutrons from the first phase explosion bombard the lithium. Meanwhile, the high temperature generated by the fission explosion caused the fusion reactions of the deuterium and tritium. The third phase was the fission reaction of the layer of uranium 238 (natural uranium or depleted uranium) surrounding the thermonuclear fuel. The very-high energy neutrons released from the fusion reactions can fission uranium 238. For a layer-cake-type model, additional layers of thermonuclear materials and uranium 238 could be used.

[38] Song Binghuan, op. cit.

[39] Liu Xiyao, ed., op. cit., p. 36.

[40] The Editing Committee, Essay collection for academician Yu Min’s 80th birthday celebration, Atomic Energy Press, Beijing, 2006 (in Chinese), p. 137.

[41] Liu Xiyao, ed., op. cit., p. 57.

[42] Zheng Shaotang and Zeng Xiancai, Yu Min, op. cit., p. 63.

[43] The Editing Committee, 2006, op. cit., p. 158-159.

[44] Cai Shaohui, Remember the passionate moments in my heart, Physics (Chinese magazine), 2006, vol. 35, no. 9, p. 755.

[45] Liu Xiyao, ed., op. cit., p. 78.

[46] Cai Shaohui, op. cit., p. 755.

[47] The Editing Committee, 2006, op. cit., p. 159-161.

[48] Cai Shaohui, op. cit., p. 756.

[49] Liu Xiyao, ed., op. cit., p. 67.

[50] The Editing Committee, 2006, op. cit., p. 136-137.

[51] Liu Xiyao, ed., op. cit., p. 67.

[52] The Editing Committee, 2006, op. cit., p. 160.

[53] Cai Shaohui, op. cit., p. 756.

[54] Liu Xiyao, ed., op. cit., p. 73-78.

[55] Zheng Shaotang and Zeng Xiancai, op. cit., p. 71.

[56] Zheng Shaotang and Zeng Xiancai, op. cit., p. 71.

[57] Peng Jichao, The Huge Eastern Bang, Party school of the CPC Central Committee Press, Beijing, 1995 (in Chinese), p. 335.

[58] Liu Xiyao, Mountain Climbing and Through Fog—The memoir of Liu Xiyao, Wuhan University Press, Wuhan, 2000 (in Chinese), p. 117.

[59] Xue Jianyuan, The Ninth Bureau of the Second Ministry: Ten years from its establishment to its demise, The Story of Liangzi, June 7, 2017.

[60] Zheng Shaotang and Zeng Xiancai, op. cit., p. 73.

[61] Zheng Shaotang and Zeng Xiancai, op. cit., p. 73. There are different interpretations about why the Chinese chose this code-name. Unlike the “596” atomic bomb, the hydrogen bomb principle test had no official statement about its code-name 629. One former weaponeer reported that it was from “639,” the month and year when Mashal Nie instructed the Ninth Institute to work on the H-bomb in September 1963 [see, e.g., Li Zhiju, China’s Nuclear Shield, Culture and Art Press, Beijing, 2006 (in Chinese), p. 100]. The weaponeers addressed that the “639” was for the full-yield H-bomb tested in 1967, and its principle test device was reportedly code-named “629” because it was for a reduced-yield test, therefore was given a “reduced” code number. However, another weaponeer involved in the numerical simulations of both “629” and “639” H-bombs designs mentioned that the code-name 629 was not from the date, but rather was related to the device’s configuration [see, e.g., Liu Xiyao, ed., op. cit., p. 284].

[62] Xue Jianyuan, op. cit.

[63] Liu Xiyao, ed., op. cit., p. 207.

[64] Liu Xiyao, ed., op. cit., p. 244.

[65] Zheng Shaotang and Zeng Xiancai, op. cit., p. 73.

[66] Liu Xiyao, ed., op. cit., p. 225-226.

[67] Du Xiangwan, In memory of nuclear physicst—Wang Ganchang, Atomic Energy Press, Beijing, 2010 (in Chinese), p. 403.

[68] Xiong Xuelin, Cheng Kaijia, Guofang Keji University Press, Changsha, 2003 (in Chinese), p. 207-209.

[69] Cheng Junze and Long Shouzhan, ed., “Zero Time” explosion—memories of Lop Nor, Zhongshan University Press, Guangzhou, 2011 (in Chinese), p. 289.

[70] Western scholars and media still often attribute June 17, 1967 (the date of the full-yield H-bomb test) as being China’s first hydrogen bomb test. But many Chinese nuclear experts contend that the test of December 28, 1966, is in fact when China first tested its H-bomb. Although the device 629 exhibited a lower yield, it had all three elements of the hydrogen bomb—principle, material, and configuration.

[71] Xue Jianyuan, op. cit.

[72] Xie Guang, ed., China Today: Defense Science and Technology, National Defense Industry Press, Beijing, 1993 (in Chinese), vol. 1, p. 257.

[73] The Editing Committee, Essay collection for academician Chen Nengkuan’s 80th birthday celebration, Atomic Energy Press, Beijing, 2003 (in Chinese), p. 60.

[74] According to the witnesses, device 629 was placed into a large insulation tank and its total weight (including the device 629, the tank, and the bracket holding the device) was just over two tons [Liu Xiyao, ed., op. cit., p. 189 and 191]. In addition, the tank was taller (approximately 1.3 times higher) than that of the 596 tank with the same diameter. It was reported that the total weight (including the device 596, the tank, and the bracket) was about 1,500 kilograms with the device 596 itself weighing over 900 kilograms [see, e.g., Fang Zhengzhi et.al., Witness the detonation of China’s atomic bomb, Hunan Jiaoyu Press, Changsha, 2014 (in Chinese), p.151]. This suggests that the total weight of the tank and bracket for device 596 may have been over 500 kilograms. Given the weight of the tank for device 629 would be even heavier than that of device 596, the weight of device 629 itself may have been around 1,500 kilograms.

[75] Xie Guang, ed., op. cit., p. 258.

[76] Xi Quxing, A Biography of Zhu Guangya, China Youth Press, Beijing, 2017 (in Chinese), p. 259.

[77] Zheng Shaotang and Zeng Xiancai, op. cit., p. 81.

[78] Liu Xiyao, ed., op. cit., p. 305.

[79] Liu Xiyao, ed., op. cit., p. 286.

[80] Liu Xiyao, ed., op. cit., p. 327.

[81] Song Binghuan, op. cit.

[82] The Editing Committee, Essay collection for academician Zhu Guangya’s 80th birthday celebration, Atomic Energy Press, Beijing, 2004 (in Chinese), p. 30.

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David A. Wargowski
David A. Wargowski
9 days ago

This is a well written, comprehensive article where one does not have to be a nuclear physicist or nuclear weapons scientist/engineer to understand it. The illustrations are fantastic. In my opinion, this is the best account of the Red Chinese thermonuclear weapons development I have read. I would like to see a book on this subject published by Hui Zhang.

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