Strategic Defence Review 2025: The Royal Navy and Royal Fleet Auxiliary

The Royal Navy should move towards a “more powerful but cheaper and simpler fleet” with a hybrid mix of crewed, uncrewed and increasingly autonomous vessels and aircraft. This is one of the conclusions of the Strategic Defence Review (SDR), published by the government in June 2025.

The review sets out the Royal Navy’s purpose: to defend the UK, to deter and defend in the Euro-Atlantic, and to shape the global security environment.

This briefing is part of series of Commons Library briefings on the 2025 Strategic Defence Review. It examines the key elements of the review as they relate directly to the Royal Navy and Royal Fleet Auxiliary. Recommendations made by the review are highlighted in boxes. This briefing does not include commentary or reaction to the proposals.

Roles and tasks for the Royal Navy

The SDR sets out specific tasks for the Royal Navy, explicitly giving it responsibility for the protection of critical undersea infrastructure and maritime traffic, and securing the North Atlantic.

1. Defend, protect, and enhance the resilience of the UK, its Overseas Territories, and Crown Dependencies: delivering the Continuous At Sea Deterrent (CASD), the bedrock of the UK’s defence. The Royal Navy should also assume responsibility for leading and coordinating industry and wider Government in protecting critical undersea infrastructure and maritime traffic.
2. Deter and defend in the Euro-Atlantic: contributing to NATO Regional Plans through the provision of: CASD; fifth-generation carrier strike capability; anti-submarine warfare, with a focus on securing the North Atlantic through its Atlantic Bastion plan; littoral strike; and Type 45 destroyers providing Integrated Air and Missile Defence.
3. Shape the global security environment: using Defence levers where the Navy can deliver the greatest effect, including capability partnerships, exports, and training and education, enhanced by the Navy’s permanent presence and periodic deployments beyond the Euro-Atlantic.

The Royal Navy and NATO

Contributing to NATO’s maritime plans is one of the Royal Navy’s core roles. The SDR sets out what it describes as a ‘NATO-first’ approach for UK defence, meaning that NATO should be at the heart of how defence plans, thinks and acts. More information on what this means can be found in Commons Library researching briefing Strategic Defence Review 2025: NATO.

A more lethal, integrated force

The review calls for a transformation in deterrence and defence which, among other things, will see a move toward “warfighting readiness”, combining “a more lethal, integrated force” that utilises AI and autonomy alongside more conventional warfighting capabilities, with strengthened homeland defence.

This integrated force model is at the heart of the SDR’s proposals. The SDR says there is no end state for the integrated force: its design and capabilities “must continue to evolve as threats and technologies do".

A more powerful, cheaper and simpler fleet

The SDR envisages a Royal Navy that will have a “dynamic mix of crewed, uncrewed, and increasingly autonomous surface and sub-surface vessels and aircraft” and will develop next generation capabilities such as nuclear-powered attack submarines.

This means moving towards a “more powerful but cheaper and simpler fleet”. The review calls on the armed forces as a whole to “accelerate their transition to a ‘high-low’ mix of equipment” and greater use of autonomy and Artificial Intelligence (AI).

Unlike previous defence reviews, the SDR does not set out an explicit integrated force model or size of the Royal Navy fleet. Further information on the current state of the surface fleet and future plans can be found in Commons Library research briefing UK defence in 2025: Warships and the surface fleet.

More attack submarines

The review called on the government to confirm the intended number of nuclear-powered attack submarines required in the future to “provide clarity on the required build capacity and tempo for all nuclear-powered submarines”. In his foreword to the review, the Defence Secretary did indicate a plan to "grow our nuclear-powered attack submarine fleet to up to 12".

Experimentation

The SDR suggests the Navy needs a ‘sandbox’ to test new technologies. It does not elaborate on what it meant by this term. The Navy Lookout website says the navy needs a dedicated sea area for experimentation “with no limitation on what can be tested without the need to adhere to normal SOLAS and CLOREGs rules”. These are regulations and conventions that focus on maritime safety: the Convention for the Safety of Life at Sea (SOLAS) and preventing collisions at sea (COLREG).

The Royal Fleet Auxiliary and Fleet Solid Support ships

The SDR commends the “dedicated professional seafarers” of the RFA who “underpin[s] the Royal Navy’s operational outputs” and “make a critical contribution to homeland resilience”. The review says these capabilities “must be maintained".

However, the SDR also suggests that, in non-contested environments, the Royal Navy could make use of NATO allies support vessels and commercial vessels to help replenish Royal Navy ships at sea. This, it argues, would reduce pressure on the RFA’s fleet of solid support ships and tankers.

The Royal Navy already makes use of allies’ vessels during deployments. The SDR introduces for consideration the potential use of commercial vessels for such tasks.

The PDF of this briefing explores each of these recommendations in more detail.