Possible Irish Unification Could Create a Security Vacuum

Irish expert Philip Hamilton notes this in his article posted on the website of the UK’s Royal United Services Institute for Defence and Security Studies.

Northern Ireland is NATO territory. Potential Irish unification will take it out of the Alliance, but no one is prepared for it now. The constitutional side of Irish unification remains questionable, and on the defense aspect of such a development there is no ready answer at all.

But U.S. President Donald Trump, when asked in Dublin on 12 September whether he favored Irish unification, replied that it would be ‘a very cool thing, to be honest’. Yet he apparently overlooked the defense aspects of shifting UK and Irish borders.

The British Royal Air Force’s quick reaction alert covers Irish airspace under an arrangement struck in 1952 and updated after 9/11, to cover renegade civilian aircraft. On the other hand, Ireland is currently unable to discharge its defense responsibilities in respect of the island.

The Irish Defence Forces stood at 7,756 at the end of 2025 against an establishment of 9,739. The Naval Service has eight hulls, can crew only four, and by September of this year had two vessels deployable – none of them fitted with air search radar.

The Air Corps has no combat aircraft, and no interceptors. The State has no primary radar, i.e. no independent means of knowing what is in Irish airspace: a pilot landing in Dublin reported a large drone some 10 miles off Howth on 8 September, and air traffic control had no radar return on the object at all. Ground-based air defense consists of six systems with a maximum engagement range of 9 km.

In February, the Defence Forces informed An Garda Síochána, the Irish police, that they could not provide counter-drone security for various meetings of Ireland’s forthcoming presidency in the EU Council. An attempt was then made to train Irish soldiers how to bring down drones with shotguns.

On 28 June 2026 a French frigate maneuvered in the Irish Sea. It remained outside Irish territorial waters, with two Irish vessels operating nearby. The French crews had to be issued with Irish tactical radios, as the Irish Defence Forces hold no NATO-standard communications equipment.

In early September a British warship provided air defense for a meeting of EU foreign and defense ministers in Wicklow, remaining 14 miles offshore for the same reason.

Unification would extend an Irish air policing obligation over the airspace of the North, while leaving the Republic reliant on the air force of the State it had just supplanted there. It would remove from the Alliance’s treaty area a territory whose security NATO has never had to seriously contemplate losing.

But capability can be purchased; intelligence networks and institutions cannot. National security in Northern Ireland is reserved to Westminster and discharged by the Security Service – functions which cannot be transferred by simple declaration or renaming. Northern Ireland-related counterterrorism accounted for around 16% of the British Security Service’s resources in 2024, and there is no Irish body waiting to inherit that burden. The intelligence function has no Irish successor, which cannot be reasonably established within a transition period.

Original publication: https://www.rusi.org/explore-our-research/publications/commentary/no-good-answer-who-would-defend-united-ireland