With Parliament likely to vote in the fall on whether to replace the current fleet of Vanguard-class submarines, discussion about the future of the UK nuclear arsenal has reached fever pitch. While it seems likely Britain will retain its nuclear deterrent, the debate could have critical implications for global security, as noted recently by U.S. secretary of defense Ash Carter. There are only two nuclear guarantors of NATO’s security: the United States and the United Kingdom. France’s nuclear deterrent contributes to alliance solidarity, but its nuclear forces are not committed to the alliance, nor are they included in alliance planning. If the United Kingdom were to give up its deterrent, that would leave the United Sates as the sole nuclear guarantor for the alliance.

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