One of the men accused of deflating a dome at the Waihopai spy base two years ago, says he felt it was necessary to protect countless people.

Peter Murnane has gone on trial in the Wellington District Court today along with Adrian Leason and Sam Land.

The trio are facing three charges each.

The Crown alleges the trio purposefully cut through two wire fences and then slashed the dome with a sickle to intentionally damage it.

Murnane told the court there is no dispute over what they did, but it was done to protect and defend all of the overseas civilians threatened by the spy base.