On 9 August, Prime Minister Brian Faulkner used the Special Powers Act to introduce internment without trial for those suspected of being involved in violence.
Between March and August 1971, sectarian street battles had become a daily experience. As marching season approached, a number of IRA bombs exploded in city centre. On 3 July, the army had declared a 36-hour curfew on the Catholic Falls Road. But policing seemed to have no effect on the IRA.
Internment was a tactic that had used successfully during the 1950s, largely because it had been brought into force on both sides of the border at the same time. But in 1971, it was a major political blunder as there was no chance that the Irish Republic, already deeply concerned with events, was going to agree to the request from Belfast. During the first morning of "Operation Demetrius" 342 people were arrested; more than 100 were released two days later as it became increasingly clear that the RUC's intelligence, based on records more than a decade old, was arguably useless.
Most of the new IRA leadership had escaped army raids by hiding in safe houses or heading south of the border. But from those who were interned, there were subsequent allegations of brutality - physical and psychological - which simply aided IRA recruitment and widespread sympathy for the republican cause.
Up until 9 August, 34 people had died in violence that year. Within three days of the announcement of internment, 22 more people had lost their lives.
Internment stayed in place and by the eve of direct rule from London in 1972, the internees numbered 924. The vast majority of them were housed in long huts at a disused airfield at Long Kesh, near Lisburn - the site that would become HM Prison Maze.
William Whitelaw, the first Northern Ireland Secretary under Direct Rule, reviewed internment and by August 1972 the number of internees had dropped to 243 - a figure that rose again as the security forces attempted to re-enter nationalist areas which had become out of bounds through rioting.
Following protests by republican prisoners demanding political status, Whitelaw introduced Special Category Status for those sentenced for crimes relating to the civil violence.
The prisoners at Long Kesh were allowed free association, extra visits, food parcels and could wear their own clothes.
Both republican and loyalist paramilitaries began to organise compounds along prisoner-of-war lines with a command structure and "a duty to escape".
By the end of 1974 there were more than 1,100 special category prisoners - about half of whom were housed at the site of the future H-Blocks.