Since 1969, the United Kingdom has always had at least one ballistic-missile submarine on patrol, giving it a nuclear deterrent that is, what the Defence Council described in 1980 as, "effectively invulnerable to pre-emptive attack". In the Strategic Defence Review published in July 1998, the government stated that once the "Vanguard" submarines became fully operational (the fourth and final one, , entered service on 27 November 1999), it would "maintain a stockpile of fewer than 200 operationally available warheads". , the UK had a stockpile of 215 warheads, of which 120 were operational. The 2010 Strategic Defence and Security Review reduced the number of warheads and missiles for the ballistic missile submarine on patrol to 40 and 8 respectively.