RHU, SCOTLAND - JANUARY 20: Royal Navy security personnel stand guard on HMS Vigilant at Her Majesty's Naval Base, Clyde on January 20, 2016 in Rhu, Scotland. HMS Vigilant is one of the UK's fleet of four Vanguard class nuclear-powered ballistic missile submarines carrying the Trident nuclear missile system. A decision on when to hold a key Westminster vote on renewing Trident submarine class is yet to be decided senior Whitehall sources have admitted. (Photo by Jeff J Mitchell/Getty Images)
