Ireland plotted to send special forces to attack BBC studios in Belfast as part of plans to invade Northern Ireland, it emerged yesterday.
With just 2,000 soldiers, they knew they could not mount a conventional military campaign against Britain's vastly superior numbers.
So strategists proposed using 'unconventional operations' - believed to mean bombings or machine-gun attacks - to help defend Catholics from loyalist mobs and gangs.
Cooler heads prevailed though.
At the same time, they would launch two infantry-company attacks, involving about 120 troops, into Derry and Newry.
But the planners admitted in the memo that such a momentous move would open the way to 'retaliatory punitive military action by United Kingdom forces on the republic.
Planners also realised the invading infantry faced being surrounded by British forces, and would need to dig in for a protracted defence.
Would it have been that easy for the British in '69?
It seemed, however, that doubts about their ability to wage such a campaign won the day, and the proposals were abandoned.
'Despite what the British military might say in relation to conventional military operations, guerilla warfare could have had them on their knees in about a year.
'At the height of the Troubles, the Provisional IRA had about 1,000 active service unit members and 60,000 armed elements were not able to control them.'
A retired senior British officer who served in Northern Ireland, Michael Dewar, said the Irish would have faced annihilation.
True sir ... but you don't have Cromwell anymore - and look what happened in '16-21.
'It is an absurdity to think that a puny military force like the Irish Army could in any form take on the British Army,' he said.
Glad we didn't have to find out. Things have a way of finding their own path.