Nuclear weapons could be sited at underground facilities inside a mountain in Northern Ireland, the Republic's intelligence chief advised his government, newly declassified files reveal.
Papers just released into the National Archives show Colonel L Buckley, then Director of Intelligence, was asked for a briefing for Minister of Foreign Affairs Peter Barry on the possibility of nuclear missiles being on the island in November 1983.
In a response marked 'Confidential', Buckley complained that he didn't have "the monitoring or surveillance systems or any such source to confirm the movements or emplacement of UK/Nato surface ships, submarines, aircraft or nuclear devices or their supporting systems in and around the territory of Northern Ireland".
Neither was there any "official information from the UN or Nato sources concerning such matters".
"Suffice to say any such information would be given the highest security classification and only be available to UK or other military personnel on the strictest 'need-to-know' basis at the highest level," he added.
But he said that the harbour at Sydenham in Belfast could accommodate Royal Navy or Nato ships "equipped with nuclear missiles or weapons". Aldergrove airport in Co Antrim and Ballykelly airport in Co Londonderry "can accommodate all UK and Nato aircraft including the Vulcan bomber".
Buckley goes on to say that a military base at Benbradagh Mountain (Ben Bradaigh) overlooking Dungiven in Co Derry, the second highest mountain in the Sperrins, which was used by US forces during the Cold War to communicate with its north Atlantic fleet, could hold nuclear weapons.
"Ben Bradaigh underground facilities NE (north east) of Dungiven has underground facilities, which were originally constructed by US forces for the storage of conventional high explosives but were subsequently redesigned and are understood to be suitable for the storage of nuclear weapons if so required," he wrote.
"I regret being unable to be more specific in relation to the question you posed, however the acquisition of such highly classified information would require a very sophisticated intelligence network which I do not have at this time at my disposal."
The files show the Irish Government asked the British Embassy in Dublin around that time for clarification on whether any nuclear weapons were sited in Northern Ireland.
In response British diplomat Iain Orr insisted there was "absolutely no question of siting cruise missiles in Northern Ireland".
"Furthermore, the British Government has no plans to install any land-based nuclear missiles, other than cruise, anywhere in the United Kingdom."
However, he added it was "not the policy of Her Majesty's Government to confirm or deny the whereabouts of sea or air-based nuclear missiles".
A separate note in the files marked 'Secret' shows Irish military intelligence carried out a reconnaissance mission of a British Army base at Forkhill, Co Armagh, after "strong rumours" that it "was being turned into some kind of a nuclear facility".
Military intelligence had done "further research and reconnaissance, most recently this week", the note from June 1985 states, and as a result has "strongly discounted the possibility".
Materials were being brought into the base in night-time convoys - fuelling local rumours - but this was done for security purposes "and not for any purposes of disguising the activity from locals", according to the official document.
It noted that there were underground facilities at Forkhill but suggested these were for accommodation and "protection in the event of a mortar attack".