I did a thread on this some years ago:
As the cab crawled along the Las Vegas Strip in the heat of a September afternoon, I wondered exactly what I was doing in Sin City. My Editor had been keen for me to get the viewpoint of Haruka Kirayoshi, the leading, what was she called, psychopolitical analyst. I had imagined meeting a...
www.alternatehistory.com
The Irish military action was never meant to be an "invasion" in any sense but more the creation of corridors to allow Catholics to move south. The other aspect of it was a diplomatic offensive aimed primarily at Washington, the aim of which was to bring American pressure to bear on the UK Government to dismantle a political and economic system which didn't look far removed from some of the excesses seen elsewhere at the time.
The British response would rapidly overwhelm the Irish and indeed would rapidly become (as happened in OTL Desert Storm in 1991) a punitive exercise. I had the British effectively destroy the Irish armed forces before a ceasefire.
The political consequences would be considerable - in Ulster, the militant Protestants would rapidly take over and it would take a second British military intervention, under pressure from Washington, to end the reign of terror. The journey from there to a peace would be long and fraught but the "Troubles" would end in 1972 rather than 25 years later. For Ireland, the ill-fated incursion would be politically disastrous for Jack Lynch and Fianna Fail which would fall apart and be replaced by a more conservative rural political force but power would consolidate around Fine Gael. Ireland would enter a period of introversion eschewing EEC membership in 1973 and remaining insular for a decade or more.
For Britain, the short-lived but successful conflict achieved with very little loss of life would be a huge fillip for Wilson's Government which would win a third term in the autumn of 1969.