The British Government had fears that a large rock off the Donegal coast could be used as a spy base 60 years ago, according to declassified documents released this week.
Concerns that the landmass known as Rockall could be used to spy on the Scottish military testing site, Hebrides Rocket Range, spurred the British to claim the territory.
A small team of military personnel were taken to Rockall in September 1955, where they raised a Union Jack and installed a plaque on the rock, the BBC reported.
The recently declassified NATO documents reveal that: "This decision of the UK government was connected with the fact that the UK government had recently decided to set up a guided missile range in South Uist, in the Outer Hebrides.
"The island of Rockall was uninhabited but this government wished to guard against the possibility of hostile agents installing themselves on the island in order to observe the effects of the tests on the South Uist range."
Rockall is an eroded volcano that stands 30m wide and 21m high above sea level. It is 230 nautical miles north of Donegal and has long been the subject of ownership disputes.
Ownership of Rockall’s nearby fisheries and the oil-rich sea-bed has been contested by Ireland, the UK, Iceland and Denmark. The dispute was finally settled in 2014, granting sovereignty to Scotland.
Last month the decades-old controversy was ignited once more, as fears came to light that Brexit could restrict Irish use of the sea area.
Eamon O'Cuiv, Fianna Fail's island affairs spokesman from Galway in Ireland's west, said: "In the event of a hard Brexit, there is a strong desire by many in the UK fishing industry to 'pull up the drawbridge' and push for a ban on non-UK fishing fleets fishing in UK waters so that the currently shared fishing zone will be the UK's and the UK's alone."
Sean O'Donoghue, CEO of the Killybegs Fishermen's Organisation on the west coast of Co Donegal agreed that Brexit could create access issues for Irish fishermen.
He said: "We can fish at the minute in Rockall as we have fishing rights there but when the UK leaves they will no longer be part of the Common Fisheries Policy and there will have to be some detailed discussions around the fisheries which are very difficult to resolve.”
Ireland has never tried to claim Rockall, but has long disregarded the UK’s ownership of it. This was formalised in 2014 when the exclusive economic zone (EEZ) limits were drawn up, following an investigation by the United Nations.