The Irish Army made plans in 1969 to invade Northern Ireland and blow up the BBC's Belfast headquarters and the city's main airport in what some critics said would have been a "Bay of Pigs" fiasco.
Codenamed Exercise Armageddon, the planned "unconventional operations" were in response to a statement by then Taoiseach (Irish prime minister) Jack Lynch that his government could no longer stand by and watch innocent people get hurt.
Security expert Tom Clonan claims the guerrilla activity would have turned Northern Ireland into Iraq.
Clonan makes the claim in a new documentary being aired this week in Ireland.
He said such operations would have drawn security forces away from from border towns, such as Newry, and opened up space for Irish troops to establish themselves there.
Clonan said the guerilla forces would have comprised Irish soldiers with Special Forces training.
“If [they] had gone north with explosives and weapons and the skills to carry out the attacks, they could have turned Northern Ireland into Iraq,” he said .
The documentary says that Lynch came under tremendous pressure from hardline nationalists in the Fianna Fáil party.
Former politician Des O'Malley, who was Lynch's parliamentary secretary and later founded the Progressive Democrats, said Kevin Boland and Neil Blaney pushed hard for an armed intervention.
"Boland was the most vocal, and Blaney was not far behind him, I think…their attitude was that the Irish government should take a very belligerent stance," O'Malley said. "They wanted overt military activity."
John Taylor, then junior home affairs minister said that Lynch's TV broadcast on August 13, 1969, in which Lynch said the Republic would "not stand by" was politically irresponsible and only inflamed the situation.
He said he was forced to order the mobilisation of 8,000 part-time B Specials to repel any such invasion.
However, TK Whittaker who was Lynch's key adviser at the time said the Taoiseach had no choice.
"I think the challenge [for Lynch] was to dissuade the hotheads, the republicans in his cabinet, from insisting that we go to the aid… [of nationalists in Northern Ireland]. I think it was a very terrifying period for him because he knew that he couldn't rely on support from major colleagues… It was hard to discern who was for peace and who was for invasion."