Collective defence: The Strategic Defence Review and capability gaps in a changing NATO

Executive summary

Context:

• The geopolitical situation facing the United Kingdom (UK) and its allies in the Euro-Atlantic is the most severe it has been for decades. The Russian economy is partially mobilised for a large-scale conventional conflict, and the People’s Republic of China (PRC) is undergoing an extraordinary military buildup and modernisation programme. 
• The next decade will be a period of transition for the security architecture of the Euro-Atlantic. The United States (US) is undergoing a reprioritisation of military posture towards the Indo-Pacific and, for the first time in many decades, free and open countries are faced with the prospect of a multi-front crisis.
• Due to a prolonged period of underinvestment in defence, European members of the North Atlantic Treaty Organisation (NATO) face a number of capability gaps, made more severe by the prospect of US force posture developments. The United Kingdom (UK) has recently appraised its own gaps in the Strategic Defence Review (SDR), published in June 2025.
• Though Britain’s investment in defence is set to rise to 3.5% of Gross Domestic Product (GDP) by 2035, it is crucial that maximum impact is achieved from these increases. His Majesty’s (HM) Government has also stressed that its defence posture will be ‘NATO first’ but ‘not NATO only’, and will therefore prioritise the Euro-Atlantic. Given this context, this Report seeks to explore which of the recommendations made in the SDR will have an outsized impact on collective defence of the Euro-Atlantic.

Questions this Report addresses:

• What is the current state of Russian military capabilities and to what extent will Russia be able to regenerate force in the future?

• What will the future American presence in Europe look like with an Indo-Pacific focused military posture?

• What are the current strengths and weaknesses of European NATO military forces, and what are the most concerning capability gaps?

• Given these gaps, which recommendations outlined in the SDR would make the most significant contribution to collective defence in the Euro-Atlantic?

Key findings:

• The Russian Armed Forces will not be able to reconstitute large armoured and mechanised formations rapidly, and will likely never regenerate significant stockpiles of reserve equipment. However, Russia will be able to reconstitute a large infantry army relatively quickly, backed by a significant number of long-range strike weapons, layered missile defences, modernising naval power and an extensive nuclear arsenal. 
• These capabilities give Russia a number of options for posing potential problem sets (either individually or in combination) to NATO in the near future, including attempts to out-escalate, out-produce, out-punish or out-interdict NATO.
• The US has made it clear since at least 2011 that it intends to refocus on the Indo-Pacific. However, while its presence in Europe reached a low point in 2013, it has since increased to bolster deterrence against an increasingly aggressive Russia. But the balance of power in the Indo-Pacific is shifting to the extent that US retrenchment from Europe – though yet to be defined – is very likely.
• The capabilities most likely to be redeployed are those most in demand by US Indo-Pacific Command (INDOPACOM). This means that the American forces most likely to be withdrawn from Europe are naval, air and missile defence assets, while the formations most likely to remain allocated to Europe are ground forces. There will also be an impact on US-led Command and Control (C2) and Intelligence, Surveillance, Targeting and Reconnaissance (ISTAR) contributions to NATO as a result of a reprioritisation towards the Indo-Pacific, but this is unlikely to be total.
• European NATO’s force posture is undergoing its most significant development for several decades, with the addition of Sweden and Finland as members as well as large increases in defence investment across the alliance. In particular, European members of NATO have expanded their land forces considerably, though these still face issues related to integration, readiness and enablers. European naval power, however, is still made up of older vessels, or vessels designed for low-intensity operations rather than peer naval conflict.
• Given these factors, European NATO faces a number of gaps in the following capabilities: Suppression and Destruction of Enemy Air Defences (SEAD/DEAD); Integrated Air and Missile Defence (IAMD); Counter-Uncrewed Aerial Systems (C-UAS); contested logistics; Anti-Submarine Warfare (ASW); nuclear arsenals; and a number of gaps within the defence industrial base (particularly in complex weapons production).
• The SDR provides a comprehensive overview of what is needed to refocus the British Armed Forces to become a ‘leading tech-enabled defence power, with an Integrated Force that deters, fights and wins through constant innovation at wartime pace’. Prioritisation was beyond the scope of the SDR, but the National Security Strategy (NSS), published later in June 2025, provided a ‘Strategic Framework’ from which to determine how the UK would best support a ‘NATO first’ defence posture.

Recommendations:

To strengthen NATO and address the capability gaps across European NATO, HM Government should:

1. Drive integration to pursue asymmetric advantage: Integration is vital to ensuring the military effect is greater than the sum of its parts. Technological, organisational and information superiority has long been a key advantage NATO has enjoyed as a force multiplier against numerically superior enemies. Efforts to achieve integration should be a priority to ensure this asymmetric advantage is maintained.

2. Focus the force to reinforce security at home and build strength abroad: In addition to an Integrated Force, the UK should move towards a Focused Force. This would see priority given to strengthening Britain’s air and naval power. Such a posture would defend the UK more efficiently, as the most serious direct military threats to Britain itself are from the sea and the air. It would also deepen the UK’s alliances and bolster collective defence more efficiently, as most NATO allies would benefit more from additional air and naval power.

3. Define a British national defence model to build resilience: Though for too many years considerations of homeland defence (and NATO Article Three obligations) have been overlooked, HM Government should not replicate resource-intensive ‘total defence’ models. Any British national defence model should be centred on cost-effectiveness.

4. Reinforce sub-strategic deterrence to deepen alliances: Were Washington to be distracted and Paris risk-averse, European NATO faces a sub-strategic nuclear gap. HM Government should take the next step in rebuilding the British sub-strategic arsenal through the exploration of a UK-built sub-strategic missile. This would strengthen Britain’s strategic indispensability in relation to its allies, with all the added influence which comes with it.
5. Expand missile production to enhance the defence industrial base: The UK has a wide-ranging defence industrial base with expertise across a number of domains, but suffers from limited capacity. Efforts to expand production should focus on a combination of the most in-demand items and UK-specific needs, with a key area being missile production (both strike weapons and interceptors).