Fornmer Taoiseach Garret FitzGerald ordered an overhaul of preparations for a mass exodus of "refugees" from Northern Ireland in the event of chaos breaking out after the Anglo-Irish Agreement.
Secret files, just released under the 30-year rule, show defence and health chiefs in Dublin were told in 1986 to update contingency plans previously drawn up in 1974 and 1975 - among the bloodiest years of the Troubles.
The revamped preparations would take into account the then new hospital at Letterkenny in Co Donegal being used for casualties and expanded Irish Army bases to house the "initial reception of refugees".
The updated contingency plan was ordered against a background of growing fears of a loyalist backlash to the 1985 accord signed between Mr Fitzgerald and Margaret Thatcher descending into a full-blown emergency.
The Irish government's Inter-departmental Committee on Wartime Emergency Preparations, which first met in October 1986, had raised the "planning assumptions in relation to Northern Ireland".
In a secret letter to the Department of Health in December, the Taoiseach's office sought confirmation that "plans previously drawn up by your department to cater for such an eventuality have been kept in place and updated to take account of developments such as the opening of the major new hospital in Letterkenny".
The contingency referred to "medical and hospital treatment of casualties".
In a similar missive to the Department of Defence, the Taoiseach's office said the likelihood of such an exodus across the border "as far as it can be foreseen" was "not particularly strong" at the time.
But it added: "However, in view of the unpredictable nature of the situation and outlook in Northern Ireland, it is considered advisable to seek confirmation that the plans previously drawn up in your department have been kept in place and updated to take account of any subsequent developments."
These included "for example some premises being no longer available or an expansion in accommodation in Army premises that could be utilised for the initial reception of refugees: it is clearly necessary that plans for this contingency should be up to date".