Britain established in 1940 the first national nuclear weapons program in the world, and this gave Britain credibility in articipating in the U.S.-led Manhattan Project during World War II. Despite the interruption in U.S.-U.K. nuclear cooperation in 1946-1958 owing to the McMahon Act, since 1958 the United States and the United Kingdom have worked closely in the nuclear domain. Indeed, since the 1962 Nassau Summit, the United States has sold submarine-launched ballistic missiles (SLBMs) and support systems to the United Kingdom. In 1980 and 1982, London chose to modernize its nuclear deterrent with Trident SLBMs. The British made a similar decision in 2006, and it may be reconfirmed in 2016 with legislation to construct a new fleet of Trident nuclear ballistic missile submarines. Britain has been motivated to remain a nuclear weapons state in order to protect its own national security interests and to contribute to the security of its NATO allies in an unpredictable international security environment.