Does the Strategic Defence Review provide the right defence posture for Britain?
The Big Ask | No. 23.2025
On Monday, 2nd June, the long-awaited Strategic Defence Review (SDR) was unveiled in Glasgow by Sir Keir Starmer, Prime Minister. The SDR outlines His Majesty’s (HM) Government’s plan for the United Kingdom’s (UK) defence spending and priorities across the next decade, with Sir Keir citing the need for Britain to adopt a ‘warfighting readiness’ stance.
The SDR commits to expanding the destroyer and frigate force to 25 warships for the Royal Navy, as well as up to 12 SSN-AUKUS nuclear submarines. It also pledges to upgrade the British nuclear deterrent, including consideration for a sub-strategic element. It commits to ‘always on’ munitions production and greater technological sophistication, but fails to increase the size of the British Army. In light of these commitments, for this week’s Big Ask, we asked eight experts: Does the Strategic Defence Review provide the right defence posture for Britain?
James Black
Deputy Director, Defence and Security, and European Lead, Space, RAND Europe
It is important to look beyond only what the SDR says or omits. Certainly, it makes for a sobering read. The reviewers try to stress the scale and growing urgency of the nuclear, conventional and sub-threshold threats to the UK. They also emphasise that any future war between the North Atlantic Treaty Organisation (NATO) and Russia – or one involving adversaries – would not be something which happens far away. Rather, it would directly touch Britain’s shores. These collapsing distinctions between ‘war’ and ‘peace’, or ‘home’ and ‘away’, necessitate a fundamental rethink of how defence does its business.
Crucially, the SDR signals a desire to adopt elements of the ‘total defence’ or whole-of-society approach long used by Nordic and Baltic countries. This includes calls for new legislation to give HM Government emergency powers to mobilise industry and society in a crisis, and an emphasis on starting a more open dialogue with the general populace about the threats which Britain faces.
However, the SDR is also constrained by what it is and isn’t. Written by three external experts, it aims to offer an independent perspective, yet is constrained to recommending, not directing. This means that it cannot make decisions on defence spending: 2.5%-3% of Gross Domestic Product (GDP) seems patently inadequate to fulfill all of its ambition, especially with the SDR separated from the cross-government Spending Review.
The SDR equally does not – and cannot – specify major cuts to existing capabilities or programmes, with such vital details to follow the upcoming Defence Investment Plan instead. And while it rightly calls for a whole-of-society approach, the reality is that defence controls few of the levers needed to achieve such a transformation.
Starting the UK down the path to wartime preparedness is a worthy, if belated, intent. The challenge will be turning ambition into action given the bureaucratic, financial and cultural barriers which persist – the perennial challenge of British defence reviews.
Fellow, Yorktown Institute
The long-awaited SDR provides some much needed clarity to industry, but leaves many unanswered questions on force levels, strategy and, ultimately, implementation. In this regard, it also fails to tell the story to the British public of why raising defence spending is important, especially with its welcome renewed focus on an all-society approach.
Al Carns, Parliamentary Under-Secretary (Minister for Veterans), perhaps puts it best: it is ‘all about making us ready for warfighting’. Given the stakes in geopolitical competition, and as a continued land war dominates defence in Europe, the document brings a welcome focus on the defence industrial base, and the need to scale up both in times of pre-war and actual conflict.
Getting that right will be fundamental to HM Government’s ambition of a so-called ‘war footing’. This is never a quick process, however – so the government must act now with urgency and clarity to achieve this.
As a directional document, it is relatively precise and clear: the geopolitical realities and threats to national security are broadly explained well. However, as a strategic document, it is let down by the lack of cohesion between the perceived ends, ways and means of achieving the reviewers’ vision.
There remain significant questions over how, for instance, HM Government will meet its ongoing fiscal commitments to 2029, let alone the financial uplift to spending 3% of Gross Domestic Product (GDP) on defence by 2034, which in itself has been poorly communicated: is it firm government policy, as first envisaged by the document, or is a mere ambition, as has been suggested by ministers?
This needs to be addressed immediately to provide reassurance to the UK’s North Atlantic Treaty Organisation (NATO) allies, but also to provide Britain’s industry the reassurance it requires to help deliver the government’s industrial strategy – crucial to achieving national resiliency, but also crucial in achieving deterrence towards its adversaries.
Senior Lecturer, Department of Defence and International Affairs, Royal Military Academy Sandhurst
The 2025 SDR paints a bleak and/or realistic assessment of the geopolitical realities for the UK. Starker than the 2021 Integrated Review and the 2023 Integrated Review Refresh, the 2025 SDR specifically speaks of Britain functioning in an increasingly multipolar international environment. The ‘rules-based international order’ is lifeless. Now the emphasis is on defending the UK against multiple challenges and threats.
The ‘NATO First’ focus casts the Indo-Pacific tilt adrift. The ‘not NATO only’ aspect relegates the Indo-Pacific to a ‘priority region’, with the SDR concentrating on the Euro-Atlantic. The ‘Global Britain’ narrative has been relegated to Role 3, ‘shaping the global security environment.’ There are no new military commitments to the Indo-Pacific beyond existing ones – the Littoral Response Group, the Global Combat Air Programme (GCAP), and AUKUS. Existing or future engagements beyond the Euro-Atlantic must not detract from the priority of deterring and defending in the Euro-Atlantic theatre, or protection of Britain (including overseas obligations).
Is this the right defence posture for our time? There are notable omissions. Given the inevitability of government financial constraints, and the scale and pace of the reinvestment needed in defence, no timescales are provided. Defence needs timescales to maintain focus and spend wisely. Likewise, it may be short-sighted to ignore the interconnectedness of the Euro-Atlantic and Indo-Pacific theatres.
Nevertheless, the SDR emphasises the enormity of the transformation required to ensure the readiness of the British Armed Forces to deter, fight and win. This SDR has wound back the global aspirations of the previous integrated reviews to prioritise peer war in the Euro-Atlantic, and stresses the seriousness and likelihood of threats to the UK. For the first time since the end of the Cold War, the SDR comes closer to the stark reality of preparing Britain for war. Defence of the realm is not only the responsibility of the Armed Forces, but also requires a ‘whole of society’ approach. That part is going to be easier said than done.
Senior Fellow, Yorktown Institute
The SDR is meant to set UK defence on a war footing, blending capabilities from across the services. In theory, this should create a force capable of rapid innovation, integrating emerging technologies across all domains. The SDR makes an enormously important contribution to British spacepower through a de facto recommendation for anti-satellite capabilities and comprehensive space-based Intelligence, Surveillance and Reconnaissance (ISR).
However, the SDR does not directly address the size and role of the army, retreating into generalities about the increase in lethality which a mature, ground force reconnaissance-fires and reconnaissance-strike complex will generate. This implies a smaller, lighter ground element, perhaps explaining HM Government’s unwillingness to commit to larger ground forces.
There are three difficulties with this concept.
First, the resourcing for such a complex is quite high, necessitating a larger ground force anyway. The UK will also need a sophisticated drone-reconnaissance architecture, along with light-footprint command centres to fuse data for targeting, generating unexpected spillover effects. Large investments in radio frequency shielding, for example, may be needed to protect new command posts, and will certainly be needed in ground-based electronic warfare.
Second, bridging the middle-tier weaponeering gap which Ukraine has revealed – that is, the gap between a four-figure artillery shell and a six-figure guided rocket – will require more kit, generating mass and demanding a larger force. A reconnaissance-fires/strike complex needs high-end, middle-tier, and low-end munitions to prosecute all targets. There will be more ‘shooters’, and thus more mass, than expected.
Third, despite the discussion of innovation, a ground force along the SDR’s limited lines would not be capable of adapting to – or innovating against – combat conditions. This is a key vulnerability since Russia likely poses a generation-long threat to European security, threatening British interests. By proposing a high-tech, data-leveraging force, the SDR ironically mortgages the army’s ability to create a more robust organisation which could learn from combat experience in the extended confrontation – and potentially protracted wars – which Russia will wage against Europe.
Co-founder (Research), Council on Geostrategy
The SDR adds another 140-odd pages to the growing corpus of British defence and national security strategies published since 2010. It contains many of the same themes of the previous integrated reviews of 2021 and 2023. Much hay was made of the Indo-Pacific ‘tilt’ in the 2021 Review, which nonetheless made it very clear that ‘the precondition for Global Britain is...the security of the Euro-Atlantic region, where the bulk of the UK’s security focus will remain.’
Notwithstanding the deployment of a couple of offshore patrol vessels and two carrier strike groups – which operated in the Euro-Atlantic, too – Britain’s tilt to the Indo-Pacific has been more diplomatic and defence industrial than military, realised through agreements such as AUKUS, the Hiroshima Accord and GCAP. And the SDR intends to maintain those commitments: it makes clear that ‘NATO First’ does not mean ‘NATO only’.
Indeed, besides proposing, albeit implicitly, that Britain explore the development of a sub-strategic nuclear deterrent (based on F-35A Lightning II Joint Combat Aircraft), perhaps the SDR’s most important recommendation is for the Royal Navy to procure up to 12 SSN-AUKUS class nuclear attack submarines. Working with Australia and the United States (US) should allow the UK to achieve greater economies of scale, meaning Britain should be able to buy more submarines than it could alone. Many of these submarines will be deployed to the North Atlantic to contain Russia’s Northern Fleet, meaning it is no longer possible to think of the Euro-Atlantic and Indo-Pacific theatres as being disconnected.
Despite its long length and repetition, the SDR is a sophisticated appraisal of the nation’s defences. The problem now is resourcing it: unless HM Government commits to a real ‘defence dividend’ – ramping investment up to 3.5% or even 5% of GDP – to deter threats to the UK and its allies, the SDR will become a missed opportunity. HM Treasury should remember: deterrence is far cheaper than war.
Research Fellow (Sea Power), Council on Geostrategy
The SDR marks a welcome recognition of the Royal Navy’s central role in defending the nation, with HM Government rightly identifying maritime security as a top national priority. The Royal Navy’s mission focuses on three core objectives: defending Britain (especially through the Continuous At Sea Deterrent), deterring threats in the Euro-Atlantic region (mainly via NATO), and shaping global security through partnerships, deployments and training missions.
The SDR sets out plans for a fleet that balances high-tech capabilities with affordability and adaptability, featuring a mix of advanced and simpler systems, integrating crewed ships with autonomous platforms. Notably, the carrier strike group will evolve with ‘hybrid’ air wings, combining F-35B aircraft, drones and long-range missiles. Anti-submarine warfare, mine-hunting, and surveillance are also being modernised using artificial intelligence (AI) and autonomous systems. The Royal Fleet Auxiliary is expected to adapt too, possibly through collaborations with commercial or allied vessels.
The Royal Navy will work with government departments and private companies on protecting undersea infrastructure and enhancing surveillance and response systems. The Atlantic Bastion strategy enhances defence of the North Atlantic against Russian submarines, using an integrated sensor network, the new Type 26 frigate, and uncrewed systems to create a layered, agile defence approach. Finally, critical plans for long-term innovation and industrial support are established, including investment in shipbuilding, flexible regulation and public-private partnerships.
While full implementation hinges on the upcoming Defence Investment Plan, from a maritime perspective, the SDR contains promising and welcome plans for a strong and resilient future navy.
Former Director General for Security Policy, Ministry of Defence (2014-2018), and Visiting Professor, King’s College London
With judicious understatement, the SDR notes in its opening chapter that ‘…the UK’s longstanding assumptions about global power balances and structures are no longer certain.’ In response, it says that Britain should be a ‘leading tech-enabled defence power’, anchored in the collective security provided by NATO, with a strategic nuclear deterrent and an ‘Integrated Force’, and underpinned by a strong ‘defence innovation and industrial base’ and a ‘whole-of-society’ approach to build national resilience. In a nutshell, it offers a blueprint for a new Warfare State, to quote the title of David Edgerton’s seminal book.
Much here is familiar. Reliance on ‘high tech’ has been the hallmark of the UK’s defence policy for decades. Highlighting the centrality of ‘industrial power’ to deterrence completes the process – begun in the 2021 Defence and Security Industrial Strategy – of discarding the once-dominant free market approach to defence procurement. But the synthesis feels new – and more coherent.
Is it the right posture? British defence has to rely on high tech because it has struggled to generate mass, and will continue to do so. Past neglect of the industrial dimension of the UK’s defence posture has left insufficient capacity for the demands of peer warfare. And, faced with intensifying sub-threshold threats, a credible defence posture relies on the active engagement of civil agencies, both inside and outside government.
So, the answer is yes. The big question is delivery – a task which the reviewers explicitly leave for HM Government. Given the international context, the 2035 horizon seems too generous. And the current financial envelope looks too taut to cover the new investment proposed. An ‘Integrated Force’ is the right idea, but its depiction lacks substance – and it is vulnerable to single service agendas. Other elements of the package have been agreed before, but never properly implemented. The challenge now is to ensure that the SDR does not suffer the same fate.
Visiting Professor, London South Bank University
Britain’s latest SDR is long on promises but short on solutions. Sir Keir claims that the UK will form the ‘leading edge’ of NATO’s innovation efforts. But how, in technology, will Britain’s £60 billion defence budget beat America’s spend of nearly $1 trillion (£739 billion)?
The contrast with Ukraine’s recent drone success is telling. While Kyiv’s attack on Russian air bases took just 18 months to prepare, the SDR team spent nearly a year just writing a report. This leisurely approach simply won’t do.
Backed by Iran and North Korea – as well as quietly by the People’s Republic of China – Russia’s full-scale invasion of Ukraine demands serious preparation. We’ve seen suspicious fires and poisonings on British soil, cyber attacks on hospitals, damaged undersea cables, and Russian intrigues from Finland to the Channel. Yet, the army is the smallest it’s been in 300 years – barely 70,000 troops, nearly matched by 64,000 Ministry of Defence bureaucrats. The UK’s ageing submarines struggle, aircraft carriers lack catapults and nuclear propulsion, and the RAF is a shadow of its former self.
The SDR promises to protect overseas territories. This, right after the Prime Minister gave away the British Indian Ocean Territory. What matters in defence isn’t percentages of GDP, but working equipment, skilled personnel and genuine readiness.
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