Based on the above review of the scope of Article 42(7) and a series of interviews with policymakers across various countries in the EU, a picture emerges of three distinct but not mutually exclusive situations in which Article 42(7) could plausibly be invoked. First, the precedent set by France has made it clear that Article 42(7) could again be invoked in response to a terrorist attack on the territory of an EU member state, not dissimilar to NATO’s invocation of Article 5 in response to 9/11. Second, given the increased prominence of hybrid threats, the article could be invoked in response to forms of armed aggression such as cyberattacks that remain below the threshold of a conventional military attack, but that nonetheless inflict significant damage on an EU member state. Finally, and politically the most sensitive, the article could be invoked as a form of collective defence in response to a conventional military attack on an EU member state. The latter becomes particularly complex if the article is invoked by an EU member state against a NATO ally, but there are also plausible scenarios in which a non-NATO EU member state could invoke the article. Each of these three situations, their potential ramifications and related strategic considerations will be discussed in turn and illustrated with a brief fictional scenario.

Bataclan 2.0: responding to a terrorist attack

When France invoked Article 42(7) in response to the Bataclan attacks, it did so both as a political statement on the need for EU solidarity and as a genuine call for assistance in its fight against Islamic terrorism.[45] The attack had taken place on French soil and was partially conducted by EU-born assailants, but was claimed by the Islamic State (IS) in retaliation for French airstrikes on targets in Syria and Iraq. In response, EU member states supported French forces in their military operations against IS in the Levant as well as their operations in Africa. They also provided non-military support such as the sharing of intelligence.[46] It is most probable that an EU member state that suffers from a significant terrorist attack orchestrated by an external actor would again invoke the Article against a non-state entity, as illustrated with the example of Scenario 1. This would be a political call to action for EU member states to join military operations and provide other forms of support such as intelligence sharing or political, diplomatic and economic measures against terrorist movements in conflict-stricken or fragile states that either lack the will or the ability to take action themselves.

Scenario 1 – “Bataclan 2.0”

It is February 2022. Sweden is rocked by a series of simultaneous bombings in Stockholm, Gothenburg and Malmö that kill more than 80 people. The attacks are claimed by the Islamic State in the Greater Sahara as retaliation for Sweden’s leading role in the command of Task Force Takuba in the Sahel. After days of consultations in the Political and Security Committee, Sweden formally invokes Article 42(7) TEU and asks other EU member states for military support and all possible capabilities to reinforce Task Force Takuba.

In this scenario of a major terrorist attack, the relationship between Article 42(7) and Article 222 depends on the political aims and capacity of the invoking country. As described in chapter 2, a large EU member state may well prefer only to invoke Article 42(7), which would squarely put it in control of the eventual response – as France did in 2015. A smaller EU member state that is overwhelmed by the damage caused by the attack could opt instead to invoke Article 222 and call in support from the EU and its institutions. The main factor determining the state’s choice between the two articles is whether or not the afflicted country primarily expects assistance in retaliating against the attack or in dealing with its consequences. The potential role of the EU institutions will be further discussed in chapter 5.

Testing the threshold – Article 42(7) in response to hybrid threats

As described in chapter 2, the wording of Article 42(7) originated in the late 1940s and early 1950s, just like NATO’s Article 5. As such, its genesis far predates the emergence of new types of threats that a) emerge in the ‘grey zone’ below the threshold of conventional kinetic attacks; b) that blend together military and non-military means to destabilise an adversary; c) that are delivered in de-territorialised environments such as space or the digital domain; d) that make attribution difficult; and e) that have adversaries move up and down the escalation ladder.[47] While extensive discussions have taken place in recent years on the applicability of NATO’s Article 5 to cyberattacks or other hybrid forms of aggression[48], such discussions have only recently and somewhat reluctantly begun within the EU on the applicability of Article 42(7). Federica Mogherini’s call in 2016 for the EU member states to develop a ‘common operational protocol’ to clarify the use of the article in case of a ‘wide-ranged and serious hybrid threat’ has largely remained unanswered.[49] In November 2021, in the context of the upcoming Strategic Compass, the Dutch Parliament called upon the government to advocate for the applicability of Article 42(7) to hybrid threats and to clarify the available response options and instruments.[50]

Scenario 2 – “Testing the threshold”

It is November 2022. Germany’s new ‘Ampel’ coalition has taken a tougher stance against the Russian Federation and has still not certified the Nordstream 2 pipeline, citing regulatory concerns that Russia interprets as political in nature. A large-scale cyberattack paralyses the German harbour of Hamburg, leading to significant economic damage. Subsequent electricity failures also affect primary healthcare services, in the middle of a new wave of Covid infections that have already seen intensive care wards across the country stretched to the limit.

The attack is accompanied by a disinformation campaign blaming the German authorities for incompetence, insufficient maintenance of the energy infrastructure and short-sightedness in securing energy supplies. German security services claim to have traced the cyberattack to APT ‘Turla’, a group of hackers operating from within the Russian Federation. Germany invokes Article 42(7), asking other EU member states and the EU Agency for Cybersecurity (ENISA) for assistance in repelling the continuous cyberattacks and – if the Russian Government does not cooperate in stopping the attacks – further economic sanctions against Russia. Germany also asks the EU member states and institutions for support for its healthcare system and energy infrastructure.

From interviews it becomes clear that for most EU member states hybrid threats are seen as both most relevant for a potential invocation of Article 42(7), and as most unclear as to which responses would be appropriate. A series of exercises conducted by the European External Action Service (EEAS) in a PSC format throughout 2021 have explored various scenarios, including responses to a large-scale cyberattack, various forms of disinformation campaigns, an influx of refugees and the involvement of unidentified armed actors.[51]

While there is generally a broad consensus emerging among EU member states that Article 42(7) could legitimately be invoked in response to hybrid forms of aggression, several thorny issues remain. The first is the debate over the threshold, a perennial conundrum in all forms of credible deterrence due to the preference to retain strategic ambiguity and not signal clearly to a potential adversary what the ‘red lines’ are, nor how transgressions of these lines will be responded to.[52] Like NATO allies, EU member states prefer to deliberately keep the threshold undefined and will decide on a case-by-case basis whether or not the article is to be invoked.[53] The EU also often remains ambiguous in matters of European defence “to deliberately leave room for interpretation so that potential supporters can project their wishes onto an idea, even if there is no consensus on its actual meaning”.[54] While this ambiguity is both prudent from a deterrence perspective and politically expedient to circumvent disagreements, it does make it harder for EU member states to align their perceptions and the expectations of one another. This could lead to a situation where some states could question the legitimacy of the invocation of the article and subsequently refrain from rendering meaningful assistance. This makes it imperative to run regular tabletop exercises and simulations, which help to create a common frame of reference among EU member states without embarking on counterproductive negotiations on purely hypothetical thresholds.

Second, it is as yet unclear which role EU institutions could – and should – play to counter hybrid forms of aggression. Unlike countering conventional military threats, where the EU is far less equipped to act in comparison to NATO, the EU has a wide-ranging toolbox at its disposal to respond to various forms of hybrid threats.[55] These include several of its specialised agencies and departments, such as the EU Agency for Cybersecurity (ENISA) in the case of cyberattacks, the Strategic Communications and Information Analysis Division of the EEAS that has expertise in countering disinformation campaigns, or the Frontex agency which could help to counter the ‘weaponisation’ of migration flows. The EU could also impose economic sanctions against states that it deems responsible for hybrid aggression, as it threatened to do against Belarus in 2021 in response to the migrant crisis engineered by Alexander Lukashenka. These can already be activated without resorting to Article 42(7).

However, given the strictly intergovernmental and member state-driven character of Article 42(7), it would be up to the affected member state to decide whether or not to make use of these EU instruments. Due to the sheer amount of EU institutions, departments and task forces that could potentially be involved it may be unclear to member states which instruments they could best resort to and invoke, especially in times of crisis when decisions have to be taken at extremely short notice and national institutions may be overwhelmed. In this regard the development of a ‘hybrid toolbox’, as set out in the draft Strategic Compass and as advocated by the Netherlands, could be beneficial to further clarify the available instruments that could be deployed and could help to promote coherence in the EU’s response to counter and deter hybrid threats.[56] Nevertheless, it remains an open question who would coordinate the provision of support in such instances, in particular between different EU agencies and institutions. This co-ordination challenge will be further touched upon in chapter 5.

Finally, for those 21 EU member states that are also members of NATO, the acknowledgment that both Article 42(7) and Article 5 of NATO apply to severe hybrid threats is yet another reason why there should be closer EU-NATO cooperation in countering these threats. Although this has been identified by both organisations as a key area for future cooperation and countering hybrid threats makes up roughly one-third of all the initiatives on their mutually agreed lists of concrete joint initiatives, in reality progress has been modest at best and many challenges remain. Key among these are longstanding difficulties in sharing classified information and moving beyond merely promoting staff-to-staff contacts, which would require a more strategic vision and strategic dialogue between both organisations – as well as secure communication infrastructure.[57]

Cavalcade of calamity – Invoking Article 42(7) against a conventional military attack

Most EU member states make it abundantly clear that they do not see Article 42(7) as the EU’s equivalent of NATO’s Article 5 and prefer to underline the difference between ‘mutual assistance’ and ‘collective defence’. Those EU member states that are also NATO member states will first and foremost look to NATO for collective defence, in particular when it concerns defending their territory against a powerful adversary such as the Russian Federation. It is highly unlikely that a NATO ally will only invoke Article 42(7) in case it comes under a conventional military attack from a non-NATO ally, not least because most NATO allies attach great importance to the involvement of non-EU members such as the United States and the United Kingdom in such scenarios. This makes Article 42(7) particularly relevant for those EU member states that are not members of NATO but that are in close proximity to the Russian Federation, such as Finland and Sweden. There could in theory also be situations in which countries invoke both articles: Article 5 for collective defence by NATO allies, and Article 42(7) to ask for the assistance of other EU member states.

Scenario 3 – “Cavalcade of calamity”

It is August 2022. Tensions are high in the Eastern Mediterranean, related to both gas exploration and a new influx of migrants. After several near-misses and incidents between Turkish and Greek vessels, a Turkish navy vessel accidentally rams a ship belonging to the Greek coastguard. Turkey claims that the ships were both in Turkish territorial waters; Greece claims that they were in Greek territorial waters. Tempers run high in Athens and Ankara, with spillover effects on Cyprus. Greece orders its naval forces to open fire next time a Turkish ship crosses into Greek territorial waters; a day later, a Greek warning shot accidentally hits a Turkish ship. The situation rapidly escalates as Turkish jets bomb a Greek naval base in retaliation and hostilities erupt along the contact line on Cyprus.

Cyprus and Greece jointly invoke Article 42(7), asking EU member states for military assistance to repel Turkish naval forces, to strengthen the UN peacekeeping mission in Cyprus (UNFICYP), to enforce a ceasefire and a no-fly zone over the Eastern Mediterranean, as well as demanding crippling EU sanctions against Turkey. NATO is utterly paralysed and goes through one of the deepest crises in its history as two of its allies face off against one another.

It is also possible, however, that an EU member state would invoke Article 42(7) against a NATO ally; interviews, recent studies and political statements by Greek leaders all point towards an unlikely but plausible scenario that either Greece or Cyprus could invoke the article against Turkey after a military confrontation in the Eastern Mediterranean.[58] Some interviewees also indicated that it is plausible that an EU member state that is a member of NATO could still invoke Article 42(7) in response to an attack on their territory that is not covered by the North Atlantic Treaty; the two Spanish cities of Ceuta and Melilla in Africa would be an example. Operating from this assumption and taking geographical and geopolitical factors into account, there are theoretically four sets of situations in which the article could be plausibly invoked against a conventional military attack by a state actor (see figure 1).

Figure 1
Hypothetical scenarios for invoking Article 42(7) against an external aggressor
Hypothetical scenarios for invoking Article 42(7) against an external aggressor

There is no clear playbook that can shed light on what would happen in such calamitous scenarios. EU member states would each decide on a case-by-case basis, depending on the political and military context. Such decisions would be up to the Heads of State and Government and, most likely, legal aspects would only play a relatively limited role in their calculations. Despite all discussions about European strategic autonomy, in the case of a major security crisis on the European continent its leaders are still more likely to look towards Washington than towards the EU quarter in Brussels when making their strategic considerations. The EU would most likely be seen more as an instrument to impose economic sanctions on an aggressor than as a vehicle for a credible military response. The expected responses therefore remain – and should remain – shrouded in mystery. But what is clear from all interviews and studies to date is that all sides see the invocation of Article 42(7) in all four of the abovementioned cases in the third scenario as the ultimo ratio, the article of last resort.

In the case of a non-NATO EU member state, it would already test the limits of solidarity within the EU if its members would effectively be expected to go to war against a major adversary in order to defend a fellow EU member state. The EU is neither designed nor presently equipped to handle such confrontations in the upper part of the spectrum of violence, and most likely its member states would seek security assistance in regional or ad hoc formats, possibly drawing in the United States and/or the United Kingdom through bilateral or regional security arrangements.

To make matters worse, a NATO ally invoking Article 42(7) against another NATO ally would put the alliance under immense political and diplomatic strain, a situation described in an interview as ‘catastrophic’. NATO has tried to contribute towards de-escalation between its allies in order to avoid such an existential crisis from materialising. A lack of American leadership is mentioned by some as one of the reasons why relations between Greece and Turkey could deteriorate up to the point where one NATO ally threatens to invoke an EU article against another.[59] But NATO’s attempts to mediate, including personal efforts by the Secretary General, are complicated by the fact that the alliance is designed for collective defence and lacks institutional mechanisms to adjudicate and resolve disputes between allies. It is therefore highly likely that NATO would be institutionally and politically paralysed in the case of a serious military confrontation between two of its members. This has made it imperative for most NATO allies to make all efforts to avoid such an existential crisis from ever materialising in the first place – and has therefore made Article 42(7) a powerful tool in the hands of Greece to spur the EU into action against Turkey. There are some signs that this has paid off; in fact, as discussed further in Annex 1 to this report, France’s recent step to reassure Greece by engaging in a bilateral security pact is explicitly designed to avoid Greece from having to invoke the article in the first place; and as discussed in Annex 3, both Athens and Nicosia have little “faith in the EU’s ability to provide the necessary deterrence force required to stabilize the Eastern Mediterranean”. Article 42(7) therefore serves not only as a reminder of the EU member states’ binding security commitment towards one another, but also as yet another important reason for the early and peaceful resolution of disputes between NATO allies.

Niklas Nováky, “The Invocation of the European Union’s Mutual Assistance Clause: A Call for Enforced Solidarity,” European Foreign Affairs Review 22, no. 3, (2017): 357–376.
For a good overview of the French invocation of Article 42(7) and the response by other EU member states, see Suzana Elena Anghel and Carmen-Cristina Cirlig, “Activation of Article 42(7) TEU: France's request for assistance and Member States' responses,” European Parliament Briefing, (Brussels: European Parliamentary Research Service July 2016).
For a discussion on deterrence against hybrid threats across various domains, see Tim Sweijs, Samuel Zilincik, Frank Bekkers and Rick Meessen, “A Framework for Cross-Domain Strategies against Hybrid Threats,” HCSS Report, (The Hague: January 2021).
As recently reinforced by the alliance’s Brussels Summit Communiqué of 14 June 2021, which states, among other things, that “Allies recognise that the impact of significant malicious cumulative cyber activities might, in certain circumstances, be considered as amounting to an armed attack.
European Commission, “Joint Framework on Countering Hybrid Threats: A European Union Response,JOIN 18, (6 April 2016): 18. The document concludes that “As regards preventing, responding to and recovering from hybrid threats, it is proposed to examine the feasibility of applying the Solidarity Clause Article 222 TFEU (as specified in the relevant Decision) and Art. 42(7) TEU, in case a wide-ranging and serious hybrid attack occurs. Strategic decision making capacity could be enhanced by establishing a common operational protocol.” (emphasis added).
Parliamentary Motion by the MPs Piri et al., 35 925 V, nr. 32, 18 November 2021.
Clingendael interviews, (October-November 2021).
See for example Thomas G. Mahnken and Gillian Evans, “Ambiguity, Risk, and Limited Great Power Conflict,” Strategic Studies Quarterly, (Winter 2019): 57-77.
Clingendael interviews, (October-November 2021).
See Clara Sophie Cramer and Ulrike Franke, “Ambiguous Alliance: Neutrality, Opt-Outs and European Defence,” ECFR Essay Collection, (28 June 2021).
For a good overview, see Gustav Gressel, “Protecting Europe against Hybrid Threats,” ECFR Policy Brief, (June 2019).
Ministry of Defence and Ministry of Foreign Affairs of the Netherlands, ‘Kamerbrief Kabinetsappreciatie concept Strategisch Kompas’, number BS2021026358, 10 December 2021.
Dick Zandee, Sico van der Meer and Adája Stoetman, “Countering Hybrid Threats: Steps for improving EU-NATO cooperation,” Clingendael Report, (The Hague: October 2021).
See the contribution of Constantinos Adamides in Annex 3 of this report, as well as Elie Perot, “Solidarity and deterrence in the Eastern Mediterranean: An analysis of the delicate question of collective defence between EU member states vis-à-vis Turkey,” Fondation pour la Recherche Stratégique 13 (30 June 2021).
Perot, (2021): 6; see also Annex 3 to this report.