National defence is like home security. Just as no house is fully secured against a determined break-in, no one nation can fully guarantee the defence of its national territory. Instead, both rely on the deterrent principle.

At home we lock our doors and windows and display a “neighbourhood watch” sign. We may install an alarm system, external lighting and possibly CCTV. Nevertheless, these measures can be overcome. We hope, and expect, that they will deter a break-in.

In the same way, a nation takes measures to deter external aggression. Central to these measures is the maintenance of armed forces to resist and repel attack against its territory.

However, no defence can be fully successful. The principle, in modern times, is to have sufficient military capability to deter a potential aggressor, by making it too costly for an enemy force to attack.

The minimum level of deterrence is to have a conventional capability to fight on land, at sea and in the air. The level of investment in such a capability is an indicator of a nation’s commitment to its defence, and is usually expressed as a percentage of its GDP (Gross Domestic Product).

The average rate of defence spending (Stockholm International Peace Research Institute, 2012 figures) in the EU, is 1.3 per cent of GDP, excluding the high defence budgets of UK (2.5 per cent) and Greece (2.5 per cent). However, Irish defence spending, at 0.9 per cent in 2005, dropped to 0.6 per cent in 2008 and to 0.56 per cent in 2012. This year it has dropped further to below 0.5 per cent.

Irish defence spending is now the lowest in the EU. It is even lower than Luxembourg (0.6 per cent), a landlocked country smaller than Co Mayo. Alarm bells should be ringing somewhere.

At this level of investment in defence, Ireland is lacking the minimum conventional combat capability to provide a credible defence based on the deterrent principle.

The Naval Service has no warship capable of a combat role. The Air Corps has no fighter aircraft to protect our skies. The Army has sufficient armour to participate in peacekeeping, but not enough to function on the modern battlefield.

In terms of defence spending we have two extremes in Ireland. The taxpayer in Newry is paying approximately five times more for national defence than his/her counterpart 13 miles away in Dundalk. Our friend in Newry is paying dearly for his nuclear umbrella and the UK’s strategic defence commitments. Our man in Dundalk is out in the rain with just a cloth cap and a fig leaf, hoping to get under the same umbrella if the weather turns real bad.

An additional worrying factor is that the cutbacks and various reorganisations of the past 15 years, combined with too many barracks’ closures, have reduced the Defence Forces’ previous capacity to expand rapidly in a future emergency.

However, with the means at their disposal the Defence Forces have reorganised to meet the immediate requirements for internal security at home, and for participation in peace support operations abroad. Credit is due to the Defence Forces and the Department of Defence for managing so well with reduced resources.

The Defence Forces have never been so “fit for purpose” to meet their immediate tasks. Nevertheless, the elephant (underfunding our national defence) is still in the room. He is staring back at us with baleful eyes, and hoping for a lifeline from the White Paper on the future of the national defence for 2014-24, which the Government is due to issue later this year.

Last July a Green Paper on Defence was published to promote a discussion on this subject. This was a welcome initiative. While it focused mainly on the narrower issue of policy, rather than the wider issue of defence itself, it offered a lot of useful background data to stimulate debate.

The White Paper on Defence 2014 will be about the future, not the present. So it is important that the present state of national finances should not be allowed to over-influence its vision.

The standard justification for underinvesting in defence is that there is no threat. For certain the chances at present of an (uninvited) foreign military intervention in Ireland, lie somewhere between zero and nil. Nevertheless, in the wider historical context, it can never be completely ruled out. Neither should we assume that we will have a long lead-in time to prepare for a future crisis. In this age of mass communications international crises seem to arise with very little warning.

We live in a turbulent world, and international terrorism presents a real and present threat. As the larger EU member states increase their defences against this threat, organisations such as al-Qaeda, and its affiliates, may turn their attention to softer targets like Ireland. Our vulnerability is already flagged by our low defence spending profile, available for anyone to study on the web.

Nor will protestations of our policy of military neutrality help us. Ireland has, and rightly so, participated in peace support missions, such as in Somalia, Afghanistan and Mali, that directly and indirectly, confront these same terrorist groups.

We are not neutral when jihadists put bombs on trains in London or Madrid.

However, by supporting international peace missions, our troops abroad are contributing ultimately to national defence at home.

No one is calling for increased expenditure on defence at this time – nor is this writer. The current state of public finances precludes it. However, the White Paper on Defence 2014 could outline a programme for the Defence Forces to enhance national defence, for implementation at a future time when the economy has recovered. I propose a gradual increase in Defence allocations from its current level to stabilise at around 1 per cent of GDP by 2024, that is, in the lifetime of this White Paper.

Ireland would still be at the bottom of the EU table, but this should be enough to provide the Defence Forces with the basic conventional capability that is currently lacking.

In the meantime, the steady decline of our Defence Forces should be halted. The number of personnel in the Defence Forces is at its lowest in 40 years. It should not be allowed to fall further. There should be no more structural reorganisations that weaken our military capability to respond to national emergencies. There should be no more closures of barracks in the traditional recruiting heartlands.

In the next few years we will be commemorating the sacrifices made by a previous generation to achieve our freedom. I believe the current generation is willing to defend this freedom, and support the modest steps necessary to ensure that the Defences Forces’ role in national defence is credible and effective.

Col (retd) Dorcha Lee is a former Defence Forces provost marshal and director of military police.