Two people have been arrested after attempting to enter Devonport Naval Dockyard in Plymouth. The two women, who were arrested at about 0400 GMT on Sunday, are members of the anti-nuclear group Trident Ploughshares.
They are being questioned at Charles Cross police station in Plymouth.
Trident Ploughshares campaigns against the refitting of Trident submarines at the site.
Two members of the group staged a demonstration last year against the refitting of Trident submarine HMS Vanguard at Devonport.
They gained access to HMS Vanguard and rang its alarm, prompting a security review.
Devonport is home to seven Trafalgar class nuclear-powered submarines and is to refit the navy's four Trident nuclear submarines.