The Chinese nuclear weapons program was initiated on January 15, 1955 with scientific and technical assistance from the Soviet Union. The decision made by Chinese leadership was prompted by confrontations with the United States in the 1950s, including the Korean War, the 1955 Taiwan Straits Crisis, and nuclear blackmail. Mao Zedong explained his decision to a gathering of the Chinese Communist Party Politburo in 1956:
"Now we’re already stronger than we were in the past, and in the future we’ll be even stronger than now. Not only are we going to have more airplanes and artillery, but also the atomic bomb. In today’s world, if we don’t want to be bullied, we have to have this thing."
Mao was confident that nuclear weapon capabilities would allow China to assert its "national will" toward policy goals and deter threats to national security.
Cooperation with the Soviet Union
Initial research, design, and production preparations were made with Soviet advice. The Third Ministry of Machinery Building was established in 1956 and nuclear research was conducted at Institute of Physics and Atomic Energy in Beijing. A gaseous diffusion uranium enrichment plant was constructed in Lanzhou. In 1957, China and the USSR signed an agreement on sharing defense technology that involved an atomic bomb prototype being supplied by Moscow to Beijing, technical data, and an exchange of hundreds of Russian and Chinese scientists. A joint search for uranium in China was conducted between the two countries. A location near Lake Lop Nur in Xinjiang Province was selected to be the test site with its headquarters at Malan. Construction of the test site began on April 1, 1960, involving tens of thousands of laborers and prisoners under tough conditions. It took four years to complete, although by consequence of being the sole site for nuclear testing in China for years to come, the Lop Nur test site underwent extensive expansion and is by far the world's largest nuclear weapons test site, covering around 100,000 square kilometers.
Sino-Soviet relations cooled in the period from 1958 to 1959. China was angered at the lack of Soviet assistance against India for supporting Tibetan uprisings in 1959 and granting asylum to the Dalai Lama. The Soviet Union later refused support for China in the Sino-Indian War of 1962. Khrushchev viewed the Sino-Soviet relationship to be one-sided on Soviet assistance toward Chinese military capacities and was unnerved at Mao's relatively nonchalant view on nuclear war. The Soviet Union was also engaged in test ban negotiations with the United States in 1959 in order to relax Soviet-American tensions, directly inhibiting the delivery of a prototype to China. Broader disagreements between Russian and Chinese communist ideologies escalated mutual criticism. Russia responded by withdrawing the delivery of a prototype bomb and over 1,400 Russian advisers and technicians involved in 200 scientific projects in China meant to foster cooperation between the two countries. Project 596 was named after the month of June 1959 in which it was initiated as an independent nuclear project, immediately after Nikita Khrushchev decided to stop helping the Chinese with their nuclear program on June 20, 1959 and Mao shifted toward an overhaul policy of self-reliance. By January 14, 1964, enough fissionable U-235 had been successfully enriched from the Lanzhou plant. On October 16, 1964, a uranium-235 fission implosion device, largely designed based on clues from American and European writings on implosion devices and intelligence from other country's weapons testing, weighing 1550 kilograms was detonated on a 102-meter tower.