THIS summer a "spy ship” was spotted 170 nautical miles off the south coast of Ireland. The mystery vessel had switched off its geolocation beacons and was – effectively – invisible to civilian shipping authorities.

That is already the kind of thing which makes navies nervous.

But there was something else that sent a shiver through Ireland’s tiny defence forces: the ship was bobbing on top of subsea cables connecting Europe and America.

Irish military sources said they were looking in to whether the vessel, which reports suggested had “engaged in underwater activities”, was snooping for Russia.

This was a big deal. The hard links under the Atlantic amount to global-level strategic infrastructure, including for financial transactions.

“People think ‘the cloud’ is in the sky but it’s really in the bottom of the sea,” Cathal Berry, a parliamentarian who used to be an army intelligence officer, told The Irish Sunday Times. “These sub-sea cables have always been the Achilles heel of Western economies.”

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The episode was not isolated. Last summer there were reports of Russian military intelligence mapping the same infrastructure. They did so as Tupolev bombers, their transponders switched off but watched by the RAF, skirted Ireland’s airspace.

Irish officials are also fretting about the grounding of a Ryanair jet in Belarus and a cyberattack on their health system.

Such jitters have quietly rekindled an old debate about Ireland’s defences and its neutrality, both of which are – let’s be blunt – more symbolic than real.

I think the arguments in this (for now relatively low-key) national conversation may sound familiar in Scotland.

Why? Because they echo those which took place within the SNP a decade ago when the party came out in favour of an independent Scotland staying in Nato.

SNP leaders back in 2013 had all sorts of political reasons for putting membership of their alliance in their prospectus for independence, even if it vexed some of their followers.

They hoped such a clear stance would offer reassurance to both swing voters at home and worried stakeholders abroad.

But underlying the policy lay a simple hard reality of European geopolitics: there really isn’t such a thing as neutrality.

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Take Ireland. Its official neutrality and low defence spending are part of the country’s brand, its image as a global good guy, and is backed up by a creditable record in international peace-keeping.

There are lots of Irish people who treasure the badge of neutrality and there are politicians willing to stand up for it. But is it real?

Ireland is not a full member of Nato – but it is in the alliance’s orbit, its partnership for peace programme. Irish soldiers train alongside Nato comrades, including for those blue helmet missions. Their weaponry, such as it is, is Western.

More: Ireland is in the EU and the bloc is a military pact, and one which, thanks to France, includes a nuclear-armed power. We don’t tend to think of “Europe” this way but the Lisbon Treaty introduced a mutual defence clause. This was controversial in the Republic, whose leaders came up with a political fudge to claim the state remained neutral, if in name only.

Ireland remains divided in to three camps. The first wants to uphold the old principle neutrality, which it thinks has been betrayed.

The second is relatively comfortable with with sheltering under a security blanket of Nato and the EU while enjoying some of the good will and soft power its neutral stance helps generate. (This was not, after all, a crazy strategy: it worked for decades).

A third body of opinion, however, wants to drop the charade. Last week in The Irish Times Stephen Collins, a veteran political commentator, called for his country to “be clear which side [it] is on and how it can best protect itself in the future”. His answer: closer defence co-operation with the EU.

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Not everybody fancies a political rammy about neutrality. “There is a temptation to let sleeping dogs lie,” Ben Tonra, a professor at University College Dublin, told me this week. “One of the dogs might bite you if you wake it up.”

So Ireland may just drift further in to a military alliance without really talking through the issues, at least outside the corridors of government or think tanks.

Events, however, may force a debate in to the open.

This week EU leaders – nervous about the prospect of more American isolationism – again talked of a military capacity for the bloc. That would pose questions for Ireland that could not go unanswered.

Equally, what happens if Ireland re-unites?

The Republic’s curious defence compromise – out of Nato but openly protected by it – stems from Northern Ireland.

Leaders in Dublin back in the 1940s felt they could could not join the alliance while the north was part of the UK. Equally Nato chiefs could not let the Republic go undefended while Northern Ireland was part of a member state.

The other supposedly neutral states of the EU, Finland, Austria and Sweden, are all more heavily armed than Ireland and arguably more plugged in to Nato. So is Scotland, as part of the UK but, for now, not of the EU.

The SNP has done a lot of thinking about the foreign and defence stances of the kind of independent Scotland it wants.

Scottish public discourse has not always kept up with this. Or even with the emerging and rapidly changing threats, such as disinformation or cyber attacks or the sabotage of digital infrastructure.

Much of what passes for discussion on Scottish security seems to me both stuck in the past and snagged on a single albeit very important issue: the future of Trident.

But there is more to defence than The Bomb.

The SNP vision for Scotland is multilateralist. That does not mean – as has been suggested – that it opposes unilateral nuclear disarmament. It means the party, like the governments of other small and medium-sized European nations, favours membership of multi-lateral, multi-national groupings. Right now those include the EU and Nato.

As Ireland demonstrates, the dilemma for an independent Scotland was never whether it should be neutral. It was whether it wanted to pretend to be neutral.

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