Some protesters chained themselves to crash barriers
The entrance to Devonport Dockyard has been barricaded by a group of anti-nuclear campaigners.
Police were called to the dockyard's Camel's Head gate in Plymouth at 0720 BST after protesters tied ladders together to block the entrance.
Campaign group Trident Ploughshares said they were protesting about money being spent on renewing the UK's Trident nuclear fleet.
Dockyard traffic was redirected until the barricade was removed.
About 14 people were involved in the protest.
The Ministry of Defence (MoD) told BBC News there had been a safety issue as some of the protesters had chained themselves to crash barriers.
One man was arrested by MoD Police on suspicion of obstruction of a highway.
The 33-year-old, from Plymouth, was arrested after repeatedly lying in the road and refusing to move on.
He is being held in custody at Charles Cross police station.