It is an idea that many would shudder to contemplate. Some time in the 2020s, Irish soldiers could go to war under the blue flag of the European Union.
A European army may seem like a long way off - a pipe dream of arch-federalists who want to see an EU superstate.
Sceptics will argue that a fractious continent is too diffuse in its interests to get together in a single military force.
A single European army would be bitterly opposed in the Dáil, in a country that has traditionally been neutral or non-aligned in international conflicts.
It would most likely face a constitutional challenge and mass protests on the streets.
It may look far-fetched but a continental army is envisaged by one of the most powerful players in the EU, no less a figure that the President of the European Commission, Jean-Claude Juncker.
Juncker has declared openly that the EU needs its own army in order to command respect as an international power.
Just two years ago the Commission President told the German Welt am Sonntag newspaper: "You would not create a European army to use it immediately.
"But a common army among the Europeans would convey to Russia that we are serious about defending the values of the European Union."
The idea of a pan-European fighting force goes right back to the foundations of the European Union, but it was put on hold, and it faced stiff opposition from the British, who preferred to rely on NATO to defend the continent.
Its supporters see greater opportunities now that the British, the staunchest opponents of an EU army, are leaving the club.
In a highly significant move that was overshadowed by the Brexit negotiations, the Irish Government this week signed us up for the new EU defence body Permanent Structured Cooperation, known as PESCO. We are joining with 24 other countries.
The Government insists that introduction of the body no way heralds the start of a continental army, but its critics and some of its more ardent advocates see it as a significant step along the road.
In its foundation documents, PESCO is described a crucial step towards strengthening a "common defence policy".
Although countries will be able to take part in its projects on an "opt-in, opt-out" basis, the new body will encourage far greater military cooperation than we have seen until now.
The commission has committed €1.5bn to PESCO projects by 2020, and Ireland will be obliged to boost its spending on personnel and weaponry.
One of its aims is to allow for greater interoperability between armies in Europe in training, equipment and research.
Ireland has already expressed an interest in taking part in a number of projects with EU partners including an upgrade of our maritime surveillance and the use of underwater drones to patrol the coast.
The Government also wants to take part in a centre of excellence for EU military training and work with other countries on cybersecurity. There are hopes that the training centre could be located at the Curragh Camp, where there are already plans for an institute that will focus on peacekeeping and conflict resolution.
As he sought approval for PESCO in the Dáil in recent days, the Taoiseach Leo Varadkar explained his thinking.
"My view is that a Europe that is worth building is a Europe that is worth defending," he said.
Varadkar argues that there are real threats to European security, and over the long term, Europe should provide and pay for its own defence and not be dependent on the United States in the way it has been since 1945.
Of course, Irish Defence Forces have already participated in many EU military activities, including missions in Chad and Somalia.
Defence analyst Declan Power says Irish troops have also taken part in exercises and training with the Nordic Battle Group, a 2,500-strong force combining troops from Norway, Sweden, Finland, the Netherlands and the Baltic States.
The retired Irish Brigadier General Gerald Aherne led the EU mission to Somalia, which aimed to train a new Somalian army and bring greater security to the country.
Brigadier General Aherne believes that being part of PESCO will help to save Irish lives, because it will improve the quality of training.
"When you do more training and courses with the defence forces of other nations, you can have common tactics, techniques and procedures."
EU missions bring troops of different nationalities together on operations, and this can pose problems. Aherne said he had commanded soldiers from 12 different EU nationalities on his mission in Mogadishu.
"They had 12 different rifles, 12 different spare parts and 12 different sets of ammunition. You also had two different types of amoured car."
The former General Officer Commanding of the Irish Army's Western Brigade said being part of PESCO should ensure that these soldiers had the same equipment and had more time for training together.
Although he welcomes the closer co-operation and says Europe needs to be more self-reliant in defence, he does not believe there will ever be a single European army.
"In order to have a functioning army you have to an independent intelligence capability.
"The EU has never had that capability and I don't think it ever will, because the member states will not allow it. They don't want any competition."
The creation of a continental army may still be a long way off, but there is no doubt that the arrival of PESCO marks the start of an era of much closer military cooperation.
The isolationist and erratic foreign policy of Donald Trump and incursions by Russia into Ukraine have highlighted this need, according to some analysts.
Ben Tonra, professor of international relations at UCD and an authority on European defence policy, says: "If you have threats to the East with Vladimir Putin's Russia and instability to the West with Trump, politicians are now asking if it is now time for Europe to get its act together."
EU countries between them now spend €200bn on defence every year, but, a lot of this expenditure is regarded as inefficient.
An EU video highlighted how member states spend their money on 29 different types of naval ships, 19 different tanks and armoured cars, and 16 fighter jets.
According to the video, member states could save up to €25bn a year between them if they pooled their resources.
Prof Tonra says Pesco is designed to fill existing strategic gaps on the continent: "EU states do not have enough military helicopters, or facilities for air-to-air refuelling."
According to Tonra, some gaps will be filled by states "getting a better bang for their buck" by bulk-buying equipment, which would, in turn, make life easier for forces that later have to work together on the ground.
He says Ireland will have to commit to spend more money on defence, which for long has been the "Cinderella of the public service".
The first batch of 17 PESCO schemes includes a Belgian-led project to develop submarine drones to deal with mines at sea.
Among the other new projects will be the creation of cyberattack rapid-response teams, led by Lithuania. The proposals also include a German-led "crisis response operation core" aimed at speeding up the deployment of troops to crisis situations.
Professor Tonra says PESCO is unlikely to play a key role in the territorial defence of Europe. That role is principally played by NATO, and 22 EU states in PESCO are members of that alliance.
While NATO is the main player in Europe's military defence, Tonra says the new organisation can play an important part in tackling threats from hybrid warfare.
Hybrid warfare is a buzz term in the military to define the tactics that are becoming increasingly common in a digital age. Russia is seen as the outstanding example of a country that has used unconventional and clandestine techniques to undermine its adversaries.
This includes provoking unrest in countries by deploying subversive forces.
Professor Tonra says Russian incursions in Ukraine offer an example of how the Kremlin could provoke unrest in the Baltic States which are part of the EU.
In Crimea the Kremlin deployed "little green men" - forces that were widely regarded to be Russian troops, while Moscow said they were organised local defence forces.
Russia also launched cyberattacks and propaganda campaigns against the government in Ukraine.
Recent reports of Russian meddling in political campaigns, including the election of Donald Trump, show how warfare has moved from the battlefield into cyberspace. Part of the role of PESCO may be to stop similar attacks in Europe.
Ten years ago, Russia demonstrated the effect of this kind of action when it launched a major cyberattack against an EU country, Estonia
Online services of Estonian banks, media outlets and government bodies were taken down by unprecedented levels of internet traffic, caused by the sending of waves of spam messages.
According to a BBC report, cash machines and online banking services were put out of action; government employees were unable to communicate with each other on email.
Our own government has expressed an interest in playing a role in averting such threats.
However, it plays down any talk of a European army, and EU officials insist that PESCO will merely step up cooperation.
The Taoiseach has insisted that the Government will not be spending money on heavyweight machinery such as fighter jets and aircraft carriers.
But critics have expressed concern about our involvement in what they see as a defence pact, and believe the decision to join was rushed through the Dáil without proper scrutiny.
The Labour Party's defence spokesman, Brendan Ryan, said: "We have a concern that PESCO could be the point of no return towards an ultimate EU army. This is something we have a very real fear of. We need a rigorous debate on this. We didn't get one."
Ryan argues that military integration is gathering pace due to the exit from the EU of the United Kingdom.
The Labour TD argues that rather than rushing us into PESCO, the Government should have focused on current defence forces personnel and ensuring that are being paid enough money so that they do not have to rely on social welfare supports.
Opponents of Ireland's signing up to PESCO may have described it as a "fledgling EU army", but defence analyst Declan Power says that this unlikely to come about.
"Being part of PESCO does not force us into anything. There are aspirations in Germany and France about federalism, but that does mean the other nations in the EU have to adhere to that."
Power believes joining PESCO will help the Irish Defence Forces to be properly trained and equipped to take part in peacekeeping roles.
"If we stay outside of it we would leave ourselves in a poorer position to the do the job that we like to think we are good at on international missions."
According to some accounts, France and Germany were the driving forces behind moves towards greater military cooperation.
France is believed to have favoured launching PESCO with a smaller core of committed nations ready to intervene militarily in conflict zones. But Germany wanted to open up membership to countries across the EU.
PESCO was originally envisaged as part of the EU's Lisbon Treaty but it has not been activated until now.
Not surprisingly, Jean-Claude Juncker, the man who favours an EU army, was cock-a-hoop this week, and said of the new defence organisation: "She is awake, the Sleeping Beauty of the Lisbon Treaty."
Juncker said member states, by signing up, were laying the foundations for a "European Defence Union".
It remains to be seen how deeply the Irish Defence Forces are involved in EU military operations in the near future, and whether PESCO compromises our neutrality, as its opponents fear.
It sounds like a fish shop or a supermarket what is it?
It's a new body in the European Union aimed at increasing co-operation and investment in defence.
The aim is to boost the operational readiness of armed forces and make them more cohesive.
So when are we joining?
We have already joined. PESCO was formally established on Monday with 25 EU states taking part. Twenty-two of these states are also in NATO. The Dáil voted to join last week by 75 votes to 42.
So is it a European army?
Defence Minister Paul Kehoe has insisted that this is not the case. Ireland will continue to take part in missions and projects on an "opt-in, opt-out" basis. However, several TDs have warned that it could herald the start of a continental army.
EU Commission President Jean-Claude Juncker said it would lay the foundations for a European Defence Union. But EU states will decide how far this will go.
So what will these PESCO troops get up to?
They have already agreed 17 joint projects including plans to develop submarine drones and maritime surveillance, a rapid-response initiative for cyberattacks and a centre of excellence for military training.
So how much will it cost?
The EU has agreed to spend €1.5bn a year on PESCO projects by 2020. To be a member, the Irish Government has had to commit itself to "regularly increasing defence budgets in real terms".