Operation Demetrius was a British Army operation in Northern Ireland on 9–10 August 1971, during the Troubles. It involved the mass arrest and internment (imprisonment without trial) of 342 people suspected of being involved with the Irish Republican Army (IRA), which was waging a campaign against the state. It was proposed by the Northern Ireland Government and approved by the British Government. Armed soldiers launched dawn raids throughout Northern Ireland, sparking four days of violence in which 20 civilians, two IRA members and two British soldiers were killed. All of those arrested were Irish nationalists, the vast majority of them Catholic. Due to faulty intelligence, many had no links with the IRA. Ulster loyalist paramilitaries were also carrying out acts of violence, which were mainly directed against Catholics and Irish nationalists, but no loyalists were included in the sweep.