This piece is part of Behind the Front, an FPRI project on the future of US and allied national defense.

The United Kingdom’s Defence Investment Plan (DIP) has now finally been published after substantial delay and controversy, aiming to give financial flesh to the bones of the 2025 Strategic Defence Review. On the maritime side, it commits £1.5bn to a Hybrid Navy fleet including uncrewed missile, sensor, and undersea platforms; it confirms that Atlantic Bastion will receive a further £1.5bn to rebuild anti-submarine warfare capacity in the North Atlantic; and it formally buries the Type 83 destroyer and Type 32 frigate programs in favor of a hybrid replacement concept built around a Common Combat Vessel and swarms of uncrewed platforms.

The vision is broadly right, but the United Kingdom’s persistent failure to fix structural problems in defense procurement and industrial delivery means the gap between what is announced and what is delivered on time and to budget remains the single greatest risk to the DIP’s plans actually materializing as described. Secondly, even a fully funded DIP does not get the United Kingdom to NATO’s 3.5 percent of GDP defense spending commitment quickly enough given the pace at which the threat is evolving, effectively deferring the hardest decisions to the next Parliament and beyond. Thirdly, and most fundamentally, none of this can be resolved through defense plans alone. The United Kingdom needs an honest, public conversation about what it is prepared to pay for its own security, through shifting spending priorities or raising taxes, because the current trajectory requires more money without ever asking the electorate to accept the trade-offs that this truly entails.

What Is the Hybrid Navy?

It is worth being precise about what the DIP commits to, because “Hybrid Navy” has become something of a shorthand that risks obscuring the scale of what is proposed. The plan sets out a family of uncrewed platforms: Type 91 uncrewed missile platforms, Type 92 uncrewed underwater sensing platforms, Type 93 extra-large uncrewed underwater vessels, and Type 94 uncrewed radar platforms. These are to be networked together and connected to crewed vessels via a Maritime Fighting Web—the naval branch of the wider Digital Targeting Web that runs through the entire DIP. At the center of this system sits the Common Combat Vessel (CCV), described as the “brain” that will connect and control the uncrewed elements, and which is explicitly intended to replace the retiring surface fleet of destroyers and frigates in the mid-late 2030s.

This is, in essence, a distributed lethality concept adapted for British circumstances and British budgets. Rather than replace small numbers of exquisite, expensive ships with a similarly small number of exquisite, expensive successors, the Royal Navy is betting that mass, distribution, and attrition tolerance—cheaper platforms that can be lost without catastrophic capability loss—offer a more survivable and affordable path to sea control and sea denial in a missile-saturated environment. The document is honest that the inherited plan—small numbers of large crewed platforms of the Type 83 and Type 32 programs with insufficient investment in autonomy—was both unaffordable and did not reflect the threat.

Atlantic Bastion is the more mature and more immediately consequential part of this picture. It marries a combined Type 26 anti-submarine warfare frigate force with Norway—13 hulls in total, the anchor of the Lunna House agreement, and, per the government’s own description, the largest British warship deal in history—with uncrewed surface and underwater vessels, AI-enabled acoustic detection, and enhanced protection for critical underwater infrastructure.

The carrier strand of the Hybrid Navy is less developed but conceptually significant. Project PANTHEON and Project VANQUISH aim to build a Hybrid Carrier Air Wing in which jet-powered drones operate alongside the F-35B force, while autonomous rotorcraft eventually replace Wildcat helicopters on escort vessels. This is the first serious acknowledgement that the Queen Elizabeth-class carriers, procured for a pre-drone era of naval aviation, will need to evolve their air wings rather than simply operate a fixed complement of crewed jets for the next three decades.

The Delivery Problem

The DIP’s own frankness should give readers pause rather than reassurance on the question of delivery. The Secretary of State’s foreword states plainly that 47 of 49 major defense projects were delayed or over budget, and that many were announced without adequate funding. The document’s response is a set of much-needed process reforms: a reset in financial management, a rule that new capability work only begins once it is demonstrably affordable, a growing contingency reserve rising to 2 percent of the departmental budget by 2030, and a one-off modernization fund to pay for the up-front costs of efficiencies that the Ministry of Defence has historically deprioritized. These are sensible reforms, and the emphasis on not starting programs until they are costed and deliverable is a genuine departure from the “announce now, fund later” pattern that has characterized British defense procurement for decades. But process reform, however well designed, does not by itself create shipyard capacity, shorten software integration timelines, or resolve the fact that the British exquisite-platform culture—long lead times, bespoke specifications, small production runs—sits awkwardly against the DIP’s own ambition to field autonomous mass at the pace that the war in Ukraine has demonstrated is now necessary.

Consider the timeline the plan itself sets out. By 2030, the ambition is to have brought “the first large autonomous vessels” of the Hybrid Navy into service, including a prototype uncrewed missile platform and extra-large uncrewed underwater vessels with AUKUS-derived payloads. The CCV, meant to sit at the center of the whole system, does not appear as a firm commitment until the 2030–35 tranche, where the plan speaks of building “at least six” of them. The Type 45 begins retiring from 2035. That leaves a vanishingly thin margin between the CCV’s earliest plausible entry into service and the point at which the destroyer force it is meant to succeed starts leaving the fleet, in a program area where the United Kingdom has an unbroken recent record of both platforms and enabling systems arriving years late. The CCV timeline thus depends on a genuinely novel platform succeeding on a schedule the United Kingdom has rarely achieved with far more conventional ones.

Then there is the financing model itself. A significant portion of the DIP’s ambition for maritime and autonomous capability rests not just on the core departmental budget but on mobilizing private capital: a new Defence Finance and Investment Strategy, a Defence Investors’ Advisory Group, a Multilateral Defence Mechanism being negotiated with Finland, the Netherlands and other allies, and a Defence Investment Unit tasked with turning procurement intentions into “market-facing propositions.” Some of this is sensible—there is genuine private sector appetite for defense and dual-use investment that previous governments left largely untapped—but it is also a partnership model that does not yet exist at scale, being asked to help deliver capabilities that also do not yet exist at scale. Layering novel financing mechanisms onto novel technology and a compressed delivery timeline is not necessarily wrong, but it does compound risk rather than diversify it. The plan is clear that individual private capital opportunities will only be taken forward “where there is clear value for money… and deliverability”—which is precisely the judgement the department has struggled to make accurately on 47 out of 49 recent major projects.

None of this is a reason to doubt the DIP’s operational logic. It is a reason to treat the £1.5bn headline figure, and the 2030 in-service ambition, as the opening bid in what will be a multi-year negotiation between ambition, industrial capacity, and HM Treasury—the same negotiation that has quietly hollowed out most previous British defense programs between announcement and delivery.

The Spending Trajectory

The DIP is refreshingly blunt about the security environment: NATO is warning that Russia could be capable of using military force against the alliance by the end of this decade; there is growing Russian activity in British waters; the Iran conflict has fundamentally changed the Middle East; and there is considerable American pressure on European allies to take on more of their own security burden, more quickly. Set against that assessment, the spending profile the plan commits to is oddly unhurried. NATO-qualifying defense spending rises to 2.7 percent of GDP by 2027/28, and the government has committed to 3 percent “in the next Parliament”—a phrase that, in a system where parliaments can run up to five years and the current one need not end before 2029, could mean anything from next year to the early 2030s. The headline 3.5 percent of GDP figure, aligned with the Hague Summit commitment made alongside 32 NATO allies, is not due until 2035—nine years from now, with a built-in allied review of the trajectory only in 2029.

There is some fiscal logic here. The defense budget is already rising by 27 percent in real terms between 2023/24 and 2029/30, reaching £74bn in cash terms in 2027/28, and ramping spending faster than that risks the very industrial bottlenecks and cost inflation that have undermined previous surges in defense spending. There is a real argument that industrial capacity—shipyards, factories, munitions plants, and the skilled workforce to staff all of them—is now as binding a constraint as money, and that pouring cash into the system faster than it can be usefully spent simply inflates prices rather than capability.

However, the spending trajectory still goes against the plan’s own description of the threat as immediate and worsening rather than distant and hypothetical. If NATO’s assessment is that Russia could be prepared to test the alliance militarily before the decade is out, a spending trajectory that reaches the alliance’s 3.5 percent target six years after that hypothetical window closes is, at minimum, a bet that deterrence can hold on today’s force structure and next year’s promised increment for considerably longer than the government’s own threat assessment implies is safe. The gap between threat assessment and spending pace is not unique to the United Kingdom—most European NATO members are in a similar position—but a plan that says the enemy may be ready by 2030 and then schedules the money for 2035 must answer to that inconsistency, even if every individual year-on-year increase within it is defensible.

The Conversation Britain Needs to Have

The debate about the DIP needs to widen beyond procurement mechanics and spending percentages, because defense investment cannot be fixed by the Ministry of Defence acting alone. The DIP finds £298bn over four years by growing the departmental budget in real terms and bringing in private capital, but it does not—because it is not its job to—set out what needs to be given up elsewhere in public spending to fund this, nor whether tax rises need to be considered. A rising defense budget on top of a National Health Service, a pensions system, and a welfare bill all under their own demographic and inflationary pressure is a claim on the same finite pool of national resources. Britain has not had a serious public conversation about what it is willing to sacrifice—in taxation, in other public spending, or in accepted risk—to fund the kind of armed forces that the threat environment now requires. Successive governments have found it easier to make defense spending commitments as a percentage of GDP, payable at some point in the medium term, than to have the harder conversation about which taxes rise, or which other budgets shrink, to pay for them now, while the threat the document itself describes is current rather than deferred.

This matters specifically for the Hybrid Navy because uncrewed systems are frequently sold to the public and to Parliament as a cheaper alternative to crewed platforms—a way of getting more capability without a proportionate rise in cost. Some of that is true at the margin: A Type 91 uncrewed missile platform will cost a fraction of a Type 45 destroyer to build and will not put a crew at risk if it is lost. But the wider system the DIP describes—the Maritime Fighting Web, the AI-enabled targeting infrastructure, the digital backbone that has to connect every sensor to every effector—is not cheap, and treating autonomy as primarily a cost-saving measure risks setting up exactly the kind of underfunding-by-optimism that produced 47 delayed projects out of 49 in the first place. If the public and Parliament are told that the Hybrid Navy is principally a way of doing more for less, the political consequences of the inevitable cost growth in software-defined, AI-enabled systems will land as a credibility crisis for the whole program rather than as the predictable maturing of a genuinely novel capability.

The honest position, and the one I think this government needs to put to the country explicitly, is that a serious deterrent in the 2030s costs more than 2.7 percent of GDP and considerably more than can be found through efficiency reform, private capital mobilization, and a contingency reserve alone. Getting there without either raising taxes or reducing spending elsewhere is not a plan; it is a hope that growth, private investment, and departmental reform will collectively close a gap that all the evidence of the last decade suggests they will not close on their own. The DIP is honest about almost everything except this. The political choice that would actually make the DIP’s ambitions credible rather than aspirational belongs to HM Treasury, to Parliament, and ultimately to the public. Until that choice is made explicitly, rather than deferred to the next spending review or the next Parliament, the gap between what this document promises and what the armed forces actually receive will remain, at the cost of British security.

Featured image: Royal Navy