Operation Armageddon was drawn up by Jack Lynch's south Irish government in September of 1969 outlining the possibility of a tactical intervention in the North with the intent to protect Catholic communities that had been attacked during the preceding riots in August. In the end the plan was scrapped, largely due to two factors. First, that the Irish army had little more then 2,500 combat ready troops and an army of just 12,000 compared to a massive British opposition which was also a member of NATO and thus likely to call on the US among others to back them in the event of an invasion. Second, British troops had successfully been implanted in August to protect Nationalist communities and by October rioting had effectively been brought to an end.
What if, however, the British decision to intervene went terribly wrong? What if a we bloody Sunday three years earlier and a significant degree of fighting broke out immediately between nationalists and the British Army? Popular opinion was already on the side of invasion and a number of cabinet members supported the route. If the British government had failed in taking some semblance of control over the situation, the masses may have been too loud to ignore and an invasion could have occurred, the possibility is certainly feasible.
The image below gives an accurate round up of what the plans were for Operation Armageddon, as it was code-named:
Essentially the Irish were to send a group of highly trained commandos to attack symbolic targets in Belfast
without declaring war. Thus the likely assumption would be the IRA or some other nationalist militia was much more powerful then intelligence had suggested. The British army would move to secure the city, as a governmental collapse in Belfast would likely be the final straw before a full blown ethnic civil war. With the troops away from the border, the Irish would invade and occupy the Catholic territories in order to "protect them" though clearly they would have no intention of surrendering the territory back the Britain. The aftermath of this, in my opinion, would be a one of a few results.
1) Wilson acquiesces- Harold Wilson had always been a moderate to say the least on the North Irish issue. Shortly after the end of his first premiership he laid out an extensive plan on how to reunify Ireland. In other words, he was explicitly in favour of allow the island to be ruled by the Republic. With this in mind, the chance of his simply allowing the Republic to annex the Catholic border regions certainly exists. However, this bears several significant problems, namely Belfast, unionists, and the home front. Even with the major Catholic regions in the south such as Derry surrendered, a significant Catholic population remains in Belfast. This combines with the second unionist issue as they would be unhappy to say the least in surrendering any portion of the North. Extreme amounts of confusing violence would likely follow and the situation in the rest of the North not annexed would likely devolve into darker shades of anarchy. And this is all excluding the home front. The British people were already not perfectly pleased with Wilson and IOTL voted him out in 1970. Almost certainly a crisis such as the above would force an earlier election and just as certainly the Conservatives would campaign for intervention and odds are the Conservatives win.
2) Britain launches a limited counter-offensive- Wilson, realizing the political situation both in England and Ireland, launches a limited counter-offensive to reclaim captured territory while promising to pursue peace and stability. Most important to this is avoiding any overt "retaliation" and containing the conflict to one between Ireland and the UK. This to me seems the most likely result, however again we must factor in British public opinion and whether they would be content with a simple limited counter-offensive. Furthermore, the chances of stabilisation are extremely low. The IRA would launch doubtlessly an intensive guerrilla campaign to maintain Irish control of the Catholic regions and the most likely endgame here is a much more intense Troubles then what we experienced IOTL.
3) Full blown war- While Wilson is Prime Minister I see this as the least likely response, however it does exist as a possibility and if one of the above, especially possibility 1, are attempted and then Wilson is voted out, the likelihood exponentially increases. The idea of retaliatory strikes against Ireland would bear certainly the internationalisation of the conflict. Much of the end result here would rest on the US and the special-relationship with Britain would be put in jeopardy. The American public has a long history of solidarity with Ireland, partially due to its massive Irish-decent population and the popularity of Irish food, holidays, drinks, literature, music, and culture. This would put Nixon in a bind as to how to respond, but as NATO has sworn defense to Britain, respond he must. A lack of response would be a betrayal of the NATO agreements. The end result here I see much harder to predict.
So what is everyone else's opinion? And moreover, what effect would such a conflict have on Ireland, Britain, and the whole balance of international relations, with a fissure possibly being thrown between London and Washington? And how deadly could such a war be? I'd doubt there's any chance of a British land invasion of the South unless somehow Thatcher manages to get into power a decade premature. Still, what possibilities lie there? And finally what role does the Communist East play? If the US and NATO stand with Britain, Ireland would be permanently ostracized and may look to the East, or more likely the NAM, for alliance? Could another Anglo-Irish war have changed the entire future of the Cold War?
What are everyone's thoughts?