Securing effective deterrence for peace and prosperity

War is terrible and should only be sought in the rarest of cases. War also has a habit of coming to those who do not seek it. In a contested world, the ability to choose whether to participate is vital. For the UK, we once again face just such a global environment. Crucially, the UK is not looking at a new Iraq War (2003-09) scenario in which the UK has the choice to participate or not. The world has changed for the worse and we need to adapt to that new reality. Failure to adapt to that reality was illustrated by Germany’s intelligence chief Bruno Kahl’s speedy evacuation from Ukraine in February 2022, after he chose to fly in, refusing to believe that Putin could be so rash as to launch an invasion. Looking ahead, the UK will therefore only avoid a future war so long as adversaries choose not to openly attack British interests. To exercise any agency over that future, the UK needs effective deterrence.

Rather than being an absolute, binary state, deterrence is a sieve that filters out threats of a certain size. For the past 30 years the UK’s sieve has prevented the worst dangers, limiting hostile actors to relatively minor, indirect or deniable actions. Over the past decade those incidents have become more dramatic, with numerous arson attacks, the Salisbury poisonings, bombs on cargo planes, and warning shots fired at sailing yachts, but they have not come with the realistic possibility of causing nationwide death and disruption.

That is changing. So far in 2026, military drones from Iranian proxy forces struck sovereign British bases in Cyprus, Russian submarines operated around vital undersea infrastructure that threatened the wider UK economy, and intermittent proxy violence has developed into a campaign of arson and subversion on British streets. Hostile actors now increasingly choose to act directly and openly against the UK because the UK’s conventional deterrence has failed. Trump’s language about the UK’s armed forces has been unacceptable, but his underlying message is sadly accurate.

Unlike the Cold War era, deterrence in 2026 is not as simple as offering the horrific prospect of mutual nuclear annihilation. The Continuous At-Sea Nuclear Deterrent continues to shield the UK from the worst possible eventualities. To be clear, in a world with authoritarian, expansionist, power-minded leaders, the Continuous At-Sea Nuclear Deterrent is sadly a necessity and not a luxury; it cancels out the deadliest threats that are being blithely thrown around by the Kremlin and White House alike. What has happened over the past five to ten years, however, has been a move back in time towards large conventional conflicts involving major powers.

Hostile actors now increasingly choose to act directly and openly against the UK because the UK’s conventional deterrence has failed.

The last time the UK was in such a dangerous, fluid era of geopolitics, it successfully retained the ability to choose the how and when of its involvement, even if that ended with war in 1939. Throughout the preceding decade the UK was able to choose to remain at peace even as hostile actors ripped into the status quo. Britain chose to remain at peace in 1931 (Manchuria), 1932 (Shanghai), 1935 (Ethiopia), 1936 (Spain), 1937 (China), 1938 (Austria and Sudetenland), and March 1939 (Czechoslovakia). Those decisions were underpinned by a multi-Parliament, cross-party acceptance that peace was only possible through effective conventional deterrence. For an island nation, that involved prioritising naval and aerial strength.

As a result, the Royal Navy’s active strength increased every year from 1931, and defence investment started to grow in a meaningful manner from 1935.¹ All three main future Axis powers avoided direct confrontations with the UK until after the UK itself chose to intervene after the invasion of Poland. In September 1939, the Royal Navy was the largest and most capable fleet in the world. The Royal Air Force was of comparable strength to the Luftwaffe, despite common belief to the contrary both then and now.² British-led land forces were also significant even if they were heavily reliant on the British Indian Army for global presence and on French allied forces in Europe. Early post-war historians may have bemoaned under-investment in defence and some reflected that facing one of the Axis powers sooner might have avoided the carnage, but Britain retained the ability to choose when it went to war.

What is deterrence?

Deterrence comes with many theories and definitions, but all agree that it is not an absolute state, nor does it come from capabilities alone. A warship, a fighter jet, or a tank sat unused does not impress or intimidate, even when they are ready for deployment. Those in need of repair or maintenance offer little comfort. Promised future equipment offers no deterrence at all. Deterrence is therefore really all about perception.

Britain used to understand this and performed its part well. Even in the early 17^th century, Charles I sailed his fleet up and down the English Channel as a performance to deter potential opponents. That strategy was then used to great effect by Parliament during the Civil Wars to prevent external intervention.³ Nelson was mocked for his extravagant displays after victory at the Battle of the Nile, but his heroism and theatrics led to his receiving awards from the Ottoman Sultan, the Kingdom of Naples, and Russia.⁴ Naval theatre was then a key part of the Fleet Reviews, when the Royal Navy deterred adversaries through ‘unprecedented pomp’.⁵ Navies can employ this not just on a grand scale, but on a day-to-day basis to prevent or delay wars. This has included firework displays during Asian port calls, delivering disaster relief to Imperial Japan, or more recently looming in the distance during the latter stages of the Sierra Leone civil war. The ‘ship over the horizon’, known about but unseen and often unused, has been incredibly potent in deterring hostile action. Impressing and intimidating without being explicitly threatening. In all these cases, strength on paper is translated into power via performances of capability and capacity.

Just as in a West End theatre, however, not all members of an audience will respond in the same way. Displays alone may impress some viewers, but discerning eyes look to the details to decide whether the performance is believable. For deterrence, it is not enough for a warship to sail to the scene, or aircraft to conduct patrols in an area. Expert observers need to believe that the display is a realistic one that can be reproduced repeatedly if put to the ultimate test.

Rebuilding the UK’s Deterrence in 2026

On paper, the UK possess 63 commissioned ships, 158 combat jets, and thousands of armoured vehicles. In practice, that does not translate into a genuinely available and effective fighting force. The Royal Navy and Royal Fleet Auxiliary may take years to return to being a credible fighting force and the RAF is stretched thin with issues of its own. As we have seen in recent months, this forces impossible choices in the short term, between potentially having to evacuate a British population equivalent to the City of York from the Gulf or to guard critical UK infrastructure. Worse, it encourages hostile actors to actively test the UK’s resolve in more dangerous ways. The UK increasingly appears as the weak link in Europe, with a smaller and less capable navy and air force than comparable nations, particularly France.

Reviewing the UK’s initial response to America’s war against Iran, it may have been practical and intended to serve UK interests alone, but it failed as a matter of deterrence. It was the right idea, poorly executed through lack of resources. Not having a warship ready in theatre, or at least for immediate deployment, sent an extremely poor message. Deployed warships do not need to join offensive operations, but if they are not there then you cannot respond if things turn for the worse. The act of deploying the warship dramatically tells a global audience that Britain is ready and able to defend itself, much more so than adding six jets to RAF Akrotiri. As a result of the poor messaging, an overstretched Royal Navy has been mauled by the international press, damaging a precious reputation that took centuries to build. Naïve excuses that Trump did not consult allies over his intentions ring hollow when USS Gerald R. Ford’s redeployment in mid-February 2026 was widely publicised and gave two weeks’ advance warning that some sort of military action was highly likely to happen. It was an unforced error.

The UK increasingly appears as the weak link in Europe, with a smaller and less capable navy and air force than comparable nations, particularly France.

It might sound an odd statement from a historian, but dwelling on the past serves little value. The best response is to plan ahead to avoid things happening again. The UK’s conventional deterrence has failed. Very real adversaries are almost certain to push boundaries even harder over the coming weeks and months. The UK is no longer able to choose what conflict we may get thrown into. The world is back in an age of empires, only this time Europe has become potential prey rather than a predator. Fortunately for the UK, it is part of multiple defensive agreements that add to its sovereign capabilities, notably NATO and its safety net ‘Article Five’. Nonetheless, an alliance is only as strong as the commitment to it and despite having the third largest economy in NATO, the UK’s ability to contribute to NATO is in rapid decline.

The UK has of course faced multi-Parliament fiscal challenges, in which politically difficult decisions have been postponed, in part because the wider public is unwilling to accept the reality of a new world that none of us wanted – not unlike the 1930s. To make matters worse, money has been wasted on poorly managed projects, rapid changes in technology have rendered some equipment obsolete, and short-term fixes have left long-term bills. The UK’s situation in the 1930s was also poor and unwanted, however, when the time came, the necessary decisions were made in a relatively timely manner.

Spending on defence may now grow to 2.7% of GDP in 2027, a potential increase less than 0.4 percentage points from 2024.⁶ In practice that is a largely meaningless increase, given cost pressures such as the national insurance rise.⁷ As a very rough historical comparison, UK spending on defence increased by 1.2 percentage points between 1935 and 1938.⁸ The UK in 2026 is therefore still in the same mindset as it was in 1934, despite facing a situation closer to 1939. Neville Chamberlain desperately sought peace, but for all the criticism he has faced, defence expenditure increased by 0.8 percentage points of GDP under his premiership in the 27 months before the declaration of war. During that period, the UK launched two battleships, two aircraft carriers, numerous cruisers and destroyers, and the Spitfire entered full production.

As a result, first and foremost, the UK’s armed forces can only present an effective deterrence if Government and Parliament take effective action. The underwhelming and partially unfunded Defence Investment Plan does not aid deterrence, as it raises significant questions over the political commitment to defence. The plan also runs the risk of repeating past mistakes of false economies, with too many items seemingly backloaded until after 2030. Short-term decisions to delay expenditure often multiplies the eventual cost, spread over multiple parliaments, all just to help with the next year’s budget. For example, originally intended for replacement after 2010, twelve Type 23 frigates underwent expensive ‘life extension’ refits between 2014 and 2020; in the most extreme case, £103m was spent on HMS Iron Duke in 2019 for just three years of additional sea life. In comparison, a brand-new Type 31 frigate had a reported cost of £268m in 2021 and should come with at least twenty years of service.⁹ Delays also risk undermining effectiveness, whether from another half a decade of poor morale and weak recruitment, or simply being unable to get ships to sea or aircraft aloft. Westminster needs to better understand that short term bursts of capital expenditure can be accepted by the financial markets, when they will yield long-term reductions in operating expenditure.

The underwhelming and partially unfunded Defence Investment Plan does not aid deterrence, as it raises significant questions over the political commitment to defence.

Capabilities

In July 2026, the UK’s armed forces are in a poor position. No Astute class submarines are at sea, only a handful of major surface warships are operational, and each Vanguard nuclear armed submarine undertakes extremely long deployments due to maintenance backlogs. As the eyes of the nation, the UK currently has only one early warning ‘Wedgetail’ aircraft. The UK’s forty-seven ‘fifth generation’ F-35B will not reach full operating capability until at least 2031 and estimates suggest that the UK only has five or six combat capable on any one day.¹⁰ Even the workhorse Eurofighter Typhoon, of which the RAF has 111, is struggling with maintenance backlogs and so the number ready for action is much lower than the headline figure. In comparison, the Russian Airforce remains many times larger, despite having suffered more confirmed losses of combat jets against Ukraine than the entire RAF inventory.¹¹ On a similar comparison, the Russian Army may be losing more men every seventy to eighty days than there are in the entire regular British Army.¹² That is before we even consider aspects like ammunition, where the situation is no better. It remains unclear whether recent reports are accurate that training exercises will need to be cut to save money, undermining drilled expertise and preventing the performances required to maintain deterrence.¹³

Looking ahead, however, there are tangible reasons for us to believe that 2026 and 2027 may be the low point for UK deterrence. The Royal Navy will start to benefit from a healthy construction programme, although warships take years to build and further years to get up to full operating efficiency.¹⁴ HMS Belfast was only just ready to defend Britain in September 1939, having been ordered in 1936, long before Hitler had even occupied the Sudetenland. Let us hope that the first Type 26 and 31 frigates also arrive in time, with four currently ‘fitting out’ of which the general-purpose frigate HMS Venturer may commission first but on an unclear timeline.¹⁵ Likewise, over the next year the worst problems with the Type 45 destroyers that form Britain’s vital defence against ballistic missiles, should have been addressed by important upgrades.¹⁶ The new Common Combat Vessel concept does raise questions about what they will be capable of delivering, but theoretically they will maintain a production timeline to replace the Type 45s in the late 2030s.¹⁷ Behind these changes have been vital improvements in Dockyard facilities and personnel numbers. Getting the warships and aircraft we do have into operational state is vital. Those facilities may also be required to repair and replace any lost in a future declared or undeclared war.

The UK’s forty-seven ‘fifth generation’ F-35B will not reach full operating capability until at least 2031 and estimates suggest that the UK only has five or six combat capable on any one day.

Autonomous, uncrewed warships and aircraft will provide crucial capabilities, mass, and options for the future hybrid armed forces. The unfortunate truism through every generation of technological advancement, however, has been the need for fully crewed hulls in the water. Effective deterrence requires naval diplomacy and theatre, which are still very much human tasks. No major evacuation of civilians from a warzone has been conducted by uncrewed equipment, which emphasises the importance of it being a ‘hybrid’ future for the Royal Navy in the Defence Investment Plan that continues to include crewed warships. Further effort therefore needs to be made to improve conditions for personnel. The defence estate should not have broken windows, mould, and faulty pipework in general, but particularly not in accommodation blocks. With enough of the right kit and motivated personnel, the UK armed forces can then display to potential adversaries that we have the means, resolve, and experience to defend the UK and its interests.

Alliances and sovereign capabilities

Given the scale and growth of geopolitical threats, the UK cannot offer a truly capable and wholly sovereign conventional deterrent without politically impossible levels of expenditure. Strong and sustained deterrence requires a good transport network, world class education, and a strong economy, all of which also require investment. The UK therefore faces some tough, pragmatic diplomacy given that the single most important element of UK foreign policy since 1956, the ‘Special Relationship’, is currently highly unstable.

The US Navy of 2026 is large but only capable of fighting a two-ocean war, much like the Royal Navy of 1939 that went on to face the five-ocean conflict that developed. Given that position and the sudden retro shift in US foreign policy, the UK cannot rest on its long-established alliances. To paraphrase Admiral of the Fleet David Beatty from 1925, Trump’s America may happily exploit sitting on the sidelines to ‘pluck the chestnuts from the fire’, before demanding concessions for their protection.¹⁸

The UK therefore needs to strengthen its syndicated sovereign capabilities. Those are bilateral agreements to share strategic assets, resources, or planning to enhance the UK’s ability to choose its own path. While alliances offer the strongest bonds to share the burden of deterrence, they are not foolproof. New political leaders can bring those carefully constructed treaties crashing down. Moreover, they are only as strong as their weakest link. A broader multilayered framework of relationships that share resources, capabilities, and support mutual resilience against a wide spectrum of challenges offers a deeper breadth of solutions.

The UK therefore needs to strengthen its syndicated sovereign capabilities. Those are bilateral agreements to share strategic assets, resources, or planning to enhance the UK’s ability to choose its own path.

In 2026, the first steps for this drive are already in place via a strengthened the Joint Expeditionary Force (JEF), discussion of a ‘CANZUK-lite’, and deals with the EU or EU members. Ideally this should also broaden to include networks with more African and Asian nations who also wish to stabilise the supply chains that the world’s largest powers seek to dominate. It may also need to consider more private military links, with Ukraine’s employment of Starlink a good example of how a strategic capability was added outside of traditional alliance structures.

Mindset

Underpinning all the changes to capabilities and alliances, UK society is woefully unprepared for a contested geopolitical environment. The UK is still operating in a post-Cold War mindset, trying to atone for its recent and historic imperial sins. As a democratic nation, political commentators on both the left and right may continue to align or express solidarity with groups based upon outdated assumptions. However, we need greater cross-party acceptance that the world is moving back into an age of competing empires, none of which are really aligned with our shared UK values. While avoiding the hazards of cruder forms of nationalism, we need to find ways to encourage greater commitment to the national interest from society, business, and Westminster. Finding the path that we want the UK to take should be through debate, whether in Parliament, the media or in the pub, but without action we risk it being dictated to us.

In dangerous worlds, maintaining deterrence has always been considerably cheaper than inaction. Public sector net debt rose by 114% of GDP during the First World War and by 99% of GDP during the Second World War.¹⁹ Even as a relatively limited war of choice, the direct cost for the UK of the Iraq War 2003-2011 is believed to have been at least £8.2 billion.²⁰ Moreover, the true cost cannot be stated in pounds and pence, as it comes in human lives. We all hope against the extreme possibility of a Third World War, in which the toll might dwarf the approximately 1.5 million British lives lost during the previous two. Recent conflicts in Ukraine and the Middle East have resulted in tens of thousands of civilians killed and many more injured through direct military action, and countless excess deaths from attacks on heating and power infrastructure, food and medical systems, and so on.²¹ Given that the UK already records 20,000-50,000 excess winter deaths, then even relatively modest attacks on UK infrastructure when energy supplies are stretched could cause very significant numbers of casualties.²² Severed subsea cables or pipelines would cause far greater economic harm than the cost of backing Britain’s armed forces now. The UK does need a strong economy as its ‘fourth arm of defence’, as Sir John Simon once saw it, but even he backed greater rearmament to protect the British public when faced with a dangerous world.²³

Maintaining deterrence has always been considerably cheaper than inaction. Public sector net debt rose by 114% of GDP during the First World War and by 99% of GDP during the Second World War. Even as a relatively limited war of choice, the direct cost for the UK of the Iraq War 2003-2011 is believed to have been at least £8.2 billion.

Conclusion:

Deterrence is cheaper than conflict and comes with far fewer casualties. Deterrence is not free, however, and needs to be properly managed to offer a credible effect. The small uplift in the Defence Investment Plan is unlikely to be enough to deter the very real adversaries the UK faces in an increasingly dangerous world. It is likely that we will see a ‘hybrid’ future of defence, but half of that future will therefore still be ‘crewed’ equipment. The UK will need to invest in more crewed warships and aircraft, as they cannot be quickly or easily developed. False economies of delaying capital expenditure must be avoided, to prevent yet more money being wasted on maintenance budgets during the intervening years. A promised increase in defence expenditure is welcome, but political wrangling over relatively small increases risk undermining the actual ability of the UK to deter aggression. Westminster needs to avoid being viewed around the world as simply being ‘less complacent’ rather than truly ‘willing to defend the UK’.

1. Heaslip, M., ‘21st Century Maritime Britain in Context – 100 years on’ in Maritime Britain in the 21st Century, eds. Kate Jamieson, Kevin Rowlands, Andrew Young, (Britannia Press, Dartmouth, 2024).

Britannia Museum Trust Press, Dartmouth: 2024

2. See: Overy, R., The Bombing War, 1939-1945, (Penguin, London, 2014).

3. Davies, J.D., Pepys’s Navy: Ships, Men & Warfare, 1649-1689, (Seaforth, Barnsley, 2008).

4. Jordan, G., Rogers, N., ‘Admirals as Heroes: Patriotism and Liberty in Hanoverian England’, Journal of British Studies 28/3 (1989), pp.201-224.

5. Ruger, J., The Great Naval Game: Britain and Germany in the Age of Empire, (Cambridge, CUP, 2007).

6. https://www.gov.uk/government/publications/the-defence-investment-plan/the-defence-investment-plan-funding-explainer.

7. Kirk-Wade, E., UK Defence Spending, 9 October 2025, House of Commons Library.

8. Defence Analytical Services and Advice (DASA), Institute for fiscal studies.

9. https://www.navylookout.com/end-in-sight-for-the-royal-navys-type-23-frigate-lifex-programme/; https://www.navylookout.com/royal-navy-frigate-programme-update/; https://www.naval-technology.com/news/six-active-nine-in-service-uk-frigate-availability-static-through-2024/?cf-view; https://www.navylookout.com/another-warship-quietly-withdrawn-royal-navy-now-down-to-just-5-frigates/; https://www.naval-technology.com/news/uks-type-23-frigates-rack-up-billion-pound-upkeep-bill-since-2014/?cf-view.

10. https://www.navylookout.com/uk-f-35-fleet-stretched-by-combat-operations-and-upgrade-delays/.

11. https://www.oryxspioenkop.com/2022/03/list-of-aircraft-losses-during-2022.html.

12. https://www.aljazeera.com/news/2026/4/10/ukraine-says-russia-suffers-record-losses-of-soldiers; https://www.gov.uk/government/statistics/quarterly-service-personnel-statistics-2026/quarterly-service-personnel-statistics-1-april-2026.

13. Genevieve Holl-Allen, ‘Military Chief warns of combat training cuts under Starmer’s defence plan’, Telegraph, 16 June 2026.

14. https://www.navylookout.com/the-royal-navys-reputation-takes-a-battering/.

15. https://ukdefencejournal.org.uk/no-firm-in-service-date-for-hms-venturer/.

16. https://www.navylookout.com/hms-daring-ships-company-moves-onboard/

17. https://ukdefencejournal.org.uk/uk-to-buy-drone-command-warships-instead-of-new-destroyers/.

18. Admiral David Beatty to the Prime Minister, July 1925, National Maritime Museum, BTY 8/8.

19. OBR Public Finances Databank, May 2026.

20. Maryam Zakir-Hussain, ‘Twenty Years On: The Shocking Numbers Behind the Iraq War’, 20 March 2023, Independent (independent.co.uk).

21. https://www.ohchr.org/en/statements-and-speeches/2026/03/deputy-high-commissioner-human-rights-al-nashif-updates-council.

22. Neelam Hassan and Jenny Chapman, Report on Winter Mortality, UK Parliament Post, 9 September 2025.

23. D.J. Dutton, ‘Simon, John 1873-1954’, Oxford Dictionary of National Biography, online (2011).