The Lynch government was warned by the Army chief-of-staff about a republican threat to overthrow the institutions of the state, according to secret documents revealed under the 30-year rule.
The warning was contained in a paper on the security situation prepared by Maj Gen Thomas L. O'Carroll on August 23rd, 1971, two weeks after the introduction of internment in Northern Ireland.
Under the heading, "Interference with the democratic institutions of the State by subversive elements", he wrote: "This is seen as an urgent problem which the Defence Forces may have to meet in the near future."
His immediate predecessor as chief-of-staff, Maj Gen P.J. Delaney, had only the previous month outlined a possible armed takeover of the State by republicans and left-wingers using the disruption in Northern Ireland as a model.
In a secret memorandum, Maj Gen Delaney wrote: "Controversial social and political issues would be exploited in order to create a situation of civil disorder."
The Delaney memo also warned of a "distinct probability" that the British Army would be withdrawn from the North. "The vacuum thus created would create a situation of grave peril for the country as a whole."
Mr Ruair∅ ╙ Brβdaigh, who was president of Provisional Sinn FΘin in 1971, last night described the briefings as "flights of fancy". He suggested the military authorities were over-reacting to widespread public protests in Dublin and elsewhere against internment.
"The whole thing takes my breath away," he said. The republican focus had been on assisting people in the North and there was no intention to take over the south. Mr ╙ Brβdaigh asked: "Are we living in the same world as these people?"
Documents released in Britain show that, as prime minister, Edward Heath ignored a British Army warning that internment would only boost the IRA and damage security in the long term.
The GOC in the North, Lieut Gen Sir Harry Tuzo, told Mr Heath a week before internment was introduced that it would have a "harmful effect". Earlier he urged that, "other possibilities for disrupting the IRA should certainly be tried first".
Around the same time, a Downing Street policy "thinktank" was examining options for the future, including the expulsion of Northern Ireland from the UK, with Dublin being invited to share in the North's administration.
The Central Policy Review Staff said that if the North ceased to be part of the UK, the net saving would be "considerable". The document described defeating the IRA as a "negative aim" and suggested the territory could be redrawn, with Irish soldiers on the streets regaining the trust of an alienated Catholic community.
The confidential report noted: "The fact that Northern Ireland is constitutionally part of the United Kingdom is no more or less relevant in terms of political realism than the fact that Algeria was part of metropolitan France."