Taiwan pursued a number of weapons of mass destruction programs from 1949 to the late 1980s. The final secret nuclear weapons program was shut down in the late 1980s under US pressure after completing all stages of weapons development besides final assembly and testing; they lacked an effective delivery mechanism and would have needed to further miniaturize any weapon before it could be effectively used in combat. Currently, there is no evidence of Taiwan possessing any chemical, biological, or nuclear weapons; but nuclear weapons from the United States have been deployed in the past during periods of heightened regional tensions with China, such as during the First Taiwan Strait Crisis. Nuclear weapons During the Cold War, the United States deployed nuclear weapons on Taiwan as part of the United States Taiwan Defense Command. In 1972, United States president Richard Nixon ordered nuclear weapons to be removed from Taiwan and this was implemented by 1974. Nuclear weapons are known to have been stored at Tainan Air Force Base. Research program The development of nuclear weapons by Taiwan has been a contentious issue, as it had been triggered by the People's Republic of China first nuclear test in 1964. The United States, hoping to avoid escalating tensions in the Taiwan Strait, has continually opposed arming Taiwan with nuclear weapons after 1979. Accordingly, Taiwan adheres to the principles of the nuclear Non-Proliferation Treaty and has stated that it does not intend to produce nuclear weapons, on an official basis. Past nuclear research by Taiwan makes it a "threshold" nuclear state. In 1967, a secret nuclear weapons program began under the auspices of the Institute of Nuclear Energy Research (INER) at the Chungshan Institute of Science and Technology. Taiwan was able to acquire nuclear technology from abroad (including a research reactor from Canada and low-grade plutonium from the United States) allegedly for a civilian energy system, but in actuality to develop fuel for nuclear weapons. Taiwan bought 100 tons of uranium metal from South Africa which was delivered between 1973 and 1974. During the 1970s, Taiwan had an active program to produce plutonium using heavy water reactors. However, after the International Atomic Energy Agency (IAEA) found evidence of Taiwan's efforts to produce weapons-grade plutonium, Taiwan agreed in September 1976 under U.S. pressure to dismantle its nuclear weapons program. A study by the Mitre Corporation in 1977, included Taiwan in a list of "insecure" nuclear