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. There is no evidence of Taiwan currently possessing any chemical, biological, or nuclear weapons.