What Strategic Outlook for Transatlantic Security?

European security is caught between a rock and a hard place. On the one hand, Russian aggression against Ukraine and the broader Euro-Atlantic architecture shows no sign of halting. In fact, the threat continues to increase, as Russia has now mobilised for protracted conflict and continues to absorb losses in a way few European countries are ready to contemplate.

On the other hand, the willingness of the US to support Ukraine unconditionally and to underwrite European security more broadly has clearly diminished. The Trump Administration expects the responsibility of defending NATO territory to be shouldered primarily by the European allies. This is largely the product of a problem of US overstretch across multiple theatres; a resource scarcity problem that is greatly exacerbated by the growing rapprochement between China, Iran, North Korea and Russia.

The good news is that this strategic problem for European security is increasingly well understood by different European capitals. Since the new NATO regional defence plans were approved at the Vilnius Summit in 2023, different analytical work strands have been trickling down into national defence establishments. As NATO approaches the upcoming summit in The Hague, the ever-green discussion about intra-alliance burden-sharing is intensifying.

Yet this should not obscure the fact that the broad contours of a rebalanced alliance have already become apparent: European allies fast-track a conventional force build-up, the US continues to underpin extended nuclear deterrence and enable force integration across the conventional and nuclear domains, and all NATO allies together embrace the defence industrial expansion that is urgently needed. In turn, this allows the discussion to shift to some hard and technical hurdles, to be overcome by remembering the cohesion of the alliance remains a key hard-nosed interest for all parties concerned.

NATO’s Conventional Force Build-Up Gets Underway

Over the past years, NATO planners have designed an elaborate family of plans for deterring conflict with the Russian Federation and defending the North Atlantic area in case of Article 5 scenarios. These plans, which cut across different geo-spatial domains and geographical regions, can only be executed if the defence establishments of individual allies are sufficiently resourced so that the collective NATO force structure does not feature meaningful gaps.

What has become readily apparent is that European allies cannot continue to rely on the prospect of large-scale US reinforcements for plugging all such gaps in crisis. In addition, US strategic enablers – many of which are swing capabilities that underpin deterrence in different theatres – may not be permanently available due to the growing risk of simultaneous conflict elsewhere in the world.

The force requirements that result from the regional plans approved in Vilnius have been integrated into the NATO defence planning process. When the Defence Ministers meet in June 2025, capability planning targets are set to be apportioned to all individual allies. Whilst it will require time and effort to build the forces in the numbers that are required – including providing for adequate training, munition stockpiling and infrastructure – the European allies now have a very granular understanding of what is required. As these plans are threat-based, the force requirements are sized and accounted for in function of possible Russian aggression, wherever it may appear.

If the US contribution to NATO is limited in scale, the resulting gap will need to be picked up by the European allies. This means that the conventional force build-up is now set to accelerate in earnest, with different European capitals rapidly increasing their defence budgets to avoid becoming the weakest link in NATO’s collective defence. As a result, intra-European pressure to invest has become as intense as the transatlantic discussion about defence spending – if not more so.

The Case for Nuclear Posture Adaptation

As Russia’s war against Ukraine has been accompanied by persistent nuclear intimidation, it has become readily apparent that NATO must plan for any Article 5 contingency to unfold under a nuclear shadow. After all, the Russian playbook of shielding its consecutive landgrabs under a barrage of nuclear threats has now unfolded repeatedly – with partial success in terms of deterring external intervention and delaying assistance to Ukraine.

When NATO leaders met in Vilnius, they not only approved conventional defence plans but also instructed their military authorities to update planning to increase the flexibility and adaptability of the alliance’s nuclear forces. This would be done with a view to making sure that ‘NATO is ready and able to deter aggression and manage escalation risks in a crisis that has a nuclear dimension’.

Whilst the increased uncertainty about the extent of US retrenchment from European security is fuelling debate about European alternatives to extended nuclear deterrence, strategic reality dictates that NATO’s nuclear deterrence remains the only viable option for countering Russian nuclear coercion, at least in the near to medium term future. Just like the conventional defence plans must be measured against the Russian conventional threat, nuclear deterrence arrangements protecting the territory of NATO allies must be measured against the Russian nuclear threat.

Unfortunately, the latter is ominously large, immediate and highly diversified across strategic and sub-strategic delivery systems and warhead yields. Such a Russian posture that is built for threatening nuclear warfighting cannot be countered with the promise of a strategic-level nuclear response alone. It instead requires a combination of strategic nuclear forces as well as diversified non-strategic nuclear strike options that neither France nor the UK can generate by themselves. This is not to say that UK or French deterrence cannot step up in a way that increases NATO deterrence, to the contrary.

If anything, the nuclear planning work that has been underway over the past two years is likely to indicate that NATO’s nuclear posture may need to evolve significantly to keep up with Vladimir Putin’s appetite for sabre-rattling. NATO’s nuclear deterrence relies on the strategic nuclear forces of France, the UK and the US as well as on forward-deployed US weapons and dual capable aircraft provided by other allies. The large disparity between NATO and the Russian Federation in terms of non-strategic systems suggests that NATO will need to bolster the theatre-level nuclear deterrence architecture. At the same time, NATO’s nuclear powers will need to consider whether their existing strategic nuclear forces suffice to deal with the two-nuclear-peer-environment that is emerging.

France and the UK can envisage expanding their strategic arsenal as well as re-introducing non-strategic strike options to help offset the pressure on the US nuclear posture. In turn, the non-nuclear NATO allies would do well to facilitate the integration of planning across the nuclear and conventional domains, and to ensure the conventional support to nuclear operations remains adequate throughout what may be a protracted campaign. This pertains not just to the number of dual capable aircraft, but also to available tanker aircraft, ground and/or sea-based air defences, stand-off munition stockpiles, and the infrastructure that is required for all of the above.

Skyrocketing Defence-Industrial Demand is Challenging Supply Chains

The force build-up that has got underway implies that European defence establishments are now expressing a skyrocketing demand signal to defence industry. This means production capacity must be scaled appropriately. Due to the gravity and the urgency of the strategic outlook, this will entail a mix between expanding co-production of systems that exist already (both in Europe and across the Atlantic) and designing new systems with more diversified and integrated supply chains.

While this discussion is receiving ample attention in European capitals and EU institutions alike, the fact remains that truly European systems will emerge only to the extent that the diversification of industrial supply chains will make that vision a practical reality. In addition, several European states will be loath to choose between European-only and transatlantic defence industrial integration for the simple reason that a combination of the two is required for meeting the capability requirements that have been identified.

Irrespective of whether the expansion of defence industrial production capacity unfolds in a purely European or in a transatlantic context, it requires a variety of technical hurdles to be overcome. When concluding security of supply agreements, trust is key, and this is easy to forfeit but hard to build. Yet beyond such questions of trust – responses to which can flipflop in function of political vagaries – lie deep-rooted structural issues. These pertain to supply chain bottlenecks concerning adequate access to raw materials, industrial workforce issues and various regulatory challenges. Addressing these effectively may well require decreasing the level of regulation and enabling swift procurement cycles to drive up production – even if this sometimes will raise thorny issues relating to export control regimes. It is arguably in these technocratic dimensions that EU-NATO cooperation can help deliver the mutually supporting ecosystem that the European defence establishments are craving for.

The Importance of NATO Cohesion

Whether one considers the ongoing build-up of European conventional forces, the debate about nuclear posture adaptation, and the defence-industrial implications of the still unfolding Zeitenwende together, one conclusion stands out. That is that European allies and the US will be in a much better position to overcome all possible hurdles by working together. The emergence of two monopolistic defence industrial blocs on both sides of the Atlantic, the questioning of extended nuclear deterrence, and the dissociation between nuclear and conventional deterrence and defence plans all constitute outcomes that would profoundly damage the alliance and the core national interests of all allies. As NATO capitals approach the summit agenda for the summit in The Hague, the importance of maintaining unity remains as paramount as ever.

© Alexander Mattelaer, 2025, published by RUSI with permission of the authors.

The views expressed in this Commentary are the authors', and do not represent those of RUSI or any other institution.

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