In 1951, China and the Soviet Union signed an agreement whereby China supplied uranium ore in exchange for technical assistance in producing nuclear weapons. In 1953, China established a research program under the guise of civilian nuclear energy. Throughout the 1950s the Soviet Union provided large amounts of equipment. But as the relations between the two countries worsened the Soviets reduced the amount of assistance and, in 1959, refused to donate a bomb for copying purposes. Despite this, the Chinese made rapid progress. Chinese first gained possession of nuclear weapons in 1964, making it the fifth country to have them. It tested its first atomic bomb at Lop Nur on October 16, 1964 (Project 596); and tested a nuclear missile on October 25, 1966; and tested a thermonuclear (hydrogen) bomb (Test No. 6) on June 14, 1967. China ultimately conducted a total of 45 nuclear tests; although the country has never become a signatory to the Limited Test Ban Treaty, it conducted its last nuclear test in 1996. In the 1980s, China's nuclear weapons program was a source of nuclear proliferation, as China transferred its CHIC-4 technology to Pakistan. China became a party to the Non-Proliferation Treaty (NPT) as a nuclear weapon state in 1992, and the Nuclear Suppliers Group (NSG) in 2004. As of 2017, the number of Chinese warheads is thought to be in the low hundreds, The Atomic Heritage Foundation notes a 2018 estimate of approximately 260 nuclear warheads, including between 50 and 60 ICBMs and four nuclear submarines. China declared a policy of "no first use" in 1964, the only nuclear weapons state to announce such a policy; this declaration has no effect on its capabilities and there are no diplomatic means of verifying or enforcing this declaration.