Reimagining the ‘arsenal ship’ for a new era

How missile mass could reshape Britain’s maritime deterrence

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Conceived during the twilight years of the Cold War by United States (US) Vice Admiral Joseph Metcalf III, the ‘arsenal ship’ was once imagined as a ‘floating missile magazine’ – a massively armed platform designed to saturate land targets overwhelmingly with hundreds of precision-guided munitions from the sea. The US Navy pursued the idea in the 1990s as part of its Revolution in Military Affairs, but enthusiasm ultimately waned amid budgetary and resource constraints, shifting priorities, and questions over vulnerability and utility at the time. The concept was quietly shelved, seen as too ambitious and inflexible for the expeditionary posture of the post-Cold War era.

Yet, history and technology rarely stand still. And evidently, today, the strategic environment has shifted once more. Cruise and ballistic missile threats are resurgent, anti-access/area denial (A2/AD) systems have vastly matured, and North Atlantic Treaty Organisation (NATO) navies – alongside those of NATO allies and partners – face growing pressures to do more with fewer ships against increasingly capable adversaries. In this context, the idea of an arsenal ship – adapted to present realities – may not only be viable, but urgently necessary. For the United Kingdom (UK), reimagining the concept offers a practical means of reinforcing homeland defence and augmenting carrier strike groups.

Strategic context and contemporary rationale

The contemporary missile threat to Britain has become increasingly diverse and challenging to defend against. Russia’s modernisation of its Northern and Baltic Fleets includes a growing inventory of long-range cruise missiles capable of striking critical infrastructure across the British Isles with minimal warning. These threats are compounded by developments in hypersonic glide vehicles and surface and subsurface-based missile platforms, which further compress reaction time and complicate interception. While the Royal Navy has taken steps to upgrade its destroyers, notably the Type 45, with limited ballistic missile defence capabilities, the total number of available ships and interceptors remains too small to defend against a full barrage confidently.

The strategic calculus is clear: the UK needs a more scalable and distributed layer of missile defence – one which is mobile, survivable and capable of protecting both British territory and forward-deployed forces. Arsenal ships, fitted with a broad spectrum of interceptors for various ranges, advanced sensors and retaliatory measures, would serve as a floating shield and sword simultaneously. It would extend the reach of the UK’s air defence network, bolster the credibility of its maritime sub-nuclear deterrence posture and reduce reliance on vulnerable land-based systems, which today remain vastly underdeveloped.

Crucially, purpose-built arsenal ships offer a more cost-effective solution than replicating high-end multi-role destroyers such as the Type 45. By focusing on missile carriage and air defence rather than broad-spectrum capabilities, it becomes possible to field more hulls at a lower cost and with smaller crews, improving coverage through distribution rather than concentration. This distributed model not only increases survivability – making it harder for an adversary to neutralise British defences in a single strike – but also enhances flexibility, allowing missile assets to be reconfigured to different theatres as threats evolve.

A shield at sea: Defending the homeland

Among its most compelling missions, a small fleet of between 8-12 Royal Navy arsenal ships would serve to reinforce national missile defence in the maritime approaches to the British Isles. Unlike fixed batteries or limited-capacity escorts, arsenal ships could carry a high volume of layered interceptors – from long-range missiles to short-range point defence systems. Positioned around UK waters and in strategic patrol areas, it could provide a comprehensive air defence system across parts – if not the entirety – of the British Isles, enhance early detection and deny adversaries confidence in a successful first strike.

The Type 31 platform, derived from the flexible and cost-effective Arrowhead 140 hull, offers a scalable foundation for an advanced arsenal ship. To meet the demands of modern missile warfare, the design would need to expand beyond its baseline fit – accommodating up to 100 missile cells through a combination of strike-length vertical launching system (VLS) cells, quad-packed common anti-air modular missile (CAMM) cells and vertical launch tubes for longer-range or strategic systems. This loadout would enable the deployment of layered defences, including area-defence interceptors such as Aster 30, short-range surface-to-air missiles (SAMs) and land attack or anti-ship cruise missiles. Integrated with upgraded long-range radar, electronic decoys, directed energy weapons and a robust combat management system, the platform could detect, classify and engage a broad spectrum of threats – ranging from hypersonic glide vehicles to sea-skimming cruise missiles – while contributing meaningfully to the UK’s wider air and missile defence architecture.

Deployed to protect key national assets or coastal approaches, a fleet of arsenal ships would increase Britain’s defensive depth. In particular, it could offer coverage for strategic military infrastructure and population centres while patrolling transit routes through which hostile platforms might launch missile attacks. Mobility would be central to its survivability. Unlike static systems, it would be a moving and self-defending target capable of redeploying in response to changing intelligence or shifting threats.

Force multiplier: Supporting naval strike groups

Beyond the explored home defence outfit, an arsenal ship would be a force multiplier for Royal Navy operations abroad. The UK’s carrier strike groups, amphibious task forces and forward-deployed warships routinely operate in regions where peer adversaries maintain advanced and dense A2/AD zones. In such environments, magazine depth becomes a critical constraint – existing specialised (and expensive) escorts can only carry so many missiles, and resupply is often slow or contested.

An arsenal-configured Type 31 would alleviate this problem. Carrying nearly 100 additional SAMs, it would bolster air defence for the wider task group, intercepting saturation attacks and protecting high-value units. Importantly, its offensive capability would also prove decisive. Equipped with land attack and anti-ship missiles, it could contribute to strike operations against enemy missile batteries, radar installations or naval forces.

This dual role – as both shield and sword – would make it indispensable in contested theatres. Operating under the Royal Navy’s evolving doctrine of distributed lethality, the arsenal ship would share targeting data with carrier aircraft, submarines and other warships. Its sensors and fire-control systems would contribute to a networked battle picture, enabling coordinated engagements and layered responses. In effect, it would act not merely as a missile repository, but as a node in a high-end decentralised maritime combat network.

Strategic implications for British sea power

Fielding arsenal ships would signal a meaningful shift in the UK’s maritime strategy. It would reflect an acknowledgement that missile defence and massed fires are now central to sea control and deterrence. Royal Navy fleets including such ships would be considerably better equipped to survive and operate in modern threat environments.

The Royal Navy’s force structure would also benefit. By supplementing high-end escorts with a missile-centric platform, Britain could extend its naval endurance and effectiveness in a more cost-effective manner without risking more valuable assets. Carrier strike groups would gain added resilience, and anti-submarine warfare frigates would be freed from secondary air defence duties.

Conclusion

The arsenal ship, once a discarded vision of another era, may yet prove a defining instrument of 21st century sea power. Reimagined for the UK’s context – focused on homeland defence, fleet support and alliance reinforcement – it meets a rising strategic need with pragmatic tools. As missile threats grow more complex and theatres grow more contested, a platform which can bring both layered defence and concentrated strike capabilities within reach offers not just deterrence, but also decisive fleet actions.

Britain would not be alone in such a move – similar concepts are being considered by several allied navies, notably South Korea with its Joint Strike Ship programme. But, by acting early and purposefully, the UK could shape the development of this emerging class of warship, rather than following it. In doing so, it would enhance the credibility of its own deterrence posture, contribute meaningfully to NATO and reaffirm the role of sea power in national strategy. In this, the arsenal ship is not a Cold War anachronism, but a timely solution to modern and emerging realities.

Samuel Harris is a recent graduate from the Department for War Studies, King’s College London, with a Master of Arts in International Relations. A former senior parliamentary staffer, he now writes independently on defence and strategic affairs, with a particular focus on British maritime strategy and air power.

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