According to the December 2006 White Paper on the Future of the United Kingdom's Nuclear Deterrent, nuclear weapons continue to provide the ultimate security guarantee. This conclusion echoes the findings of the July 1998 Strategic Defense Review [SDR]. Both reviews concluded that world is uncertain and potentially dangerous and that Britain continues to require a credible and effective minimum nuclear deterrent based on the Trident submarine force. This has provided Britain's only nuclear system since the dismantlement of the RAF's free-fall nuclear bombs in 1998. Britain's Trident force, which serves both a strategic and a "substrategic" mission, supports both Britain's security as well as the NATO alliance.