testing in Monte Bello Islands (Operation Hurricane), Emu Field and Maralinga between 1952 and 1963. Maralinga was developed as a joint facility with a shared funding arrangement. During the 1950s, Australia participated in the development of the Blue Streak missile, a Medium-range ballistic missile (MRBM) intended for delivery of a nuclear warhead. The Australian HIFAR nuclear reactor at Lucas Heights, Sydney, operated from 1958 to 2006 and has now been replaced by the OPAL reactor in 2006. The new reactor is designed to use low-enriched uranium fuel and an open pool light water system. Australia has substantial deposits of uranium which account for 30% of the world's known reserves. Until 1996 government policy restricted exploitation of uranium deposits to three established mines. A fourth site at Four Mile uranium mine was approved in July 2009. Current policy is to develop the export potential of Australia's uranium industry by allowing mining and export of uranium under strict international agreements designed to prevent nuclear proliferation. Although the RAAF continued to occasionally investigate obtaining nuclear weapons during the 1960s, Australia signed the Nuclear Non-Proliferation Treaty on 27 February 1970 and ratified the treaty on 23 January 1973. Sir Philip Baxter first head of the Australian Atomic Energy Commission (AAEC), now the Australian Nuclear Science and Technology Organisation (ANSTO) and first Vice Chancellor of the University of New South Wales openly advocated Australia acquiring a weapons grade plutonium stockpile and thus nuclear weapons. During the 1970s and 1980s, ANSTO scientists developed centrifuge enrichment technology, claimed to be comparable with the commercial URENCO centrifuge technology of the time. Such technology, if deployed on an industrial scale, would have been capable in principle of producing highly enriched uranium for nuclear weapons. The research lost government funding in the mid-1980s. A commercial-scale enrichment plant would also be capable of producing sufficient highly enriched uranium for a nuclear weapons program. An Australian company has been actively developing a novel process for uranium enrichment, Separation of Isotopes by Laser Excitation (SILEX). The Prime Minister of Australia, John Howard, began a study in 2006 into the issues surrounding an increase in Australia's uranium usage. Amongst the topics of the study were a domestic uranium enrichment plant for supplying low-enriched fuel for nuclear power reactors, either domestic or foreign. Australia is considered a nuclear threshold state. In 2019, Hugh White, a military strategist, called for Australia to have nuclear weapons. Delivery