Two protesters who boarded a Trident nuclear submarine undergoing refit at Devonport dockyard, said they had not expected to get access to the sub.
The pair said they discussed the plan for two hours
Petter Joelson, 22, told Plymouth magistrates that he and 19-year-old Elisa Silvennoinen did not have a detailed plan to get into the base.
He said: "We discussed it for maybe two hours, then got over to the base and climbed
inside to see how far we could get.
"I did not expect to be on or inside a Trident submarine."
Mr Joelson, a Swedish national from Dalmarnock Road, Glasgow, and Ms Silvennoinen, from Finland, deny causing £293 of criminal damage to a fence belonging to Devonport Management Limited on 15 November last year.
The pair were spotted by Royal Navy security personnel waving their arms and
jumping up and down on HMS Vanguard.
They had cut their way into the floodlit dry dock complex using two pairs of
18inch bolt cutters, the court heard.
Mr Joelson said they were on the submarine for about 30 minutes and spent up to
five minutes inside the conning tower.
He said he and his co-defendant were acting as weapons inspectors.
They wanted to tell people inside the base about the illegality of the
Ms Silvennoinen said they got inside the base to "prevent the greater nuclear
crime", and to protest against the "evil and immoral nuclear weapons".
Prosecutor Piers Norsworthy said the actions of the two defendants had no purpose.
"It was an act of criminal damage for publicity purposes," he said.
The case continues.