The UK Royal Navy has marked a significant dual milestone in its submarine programs with the commissioning of its sixth Astute-class nuclear-powered attack submarine (SSN), HMS Agamemnon (S125), and the ceremonial steel-cutting for the fourth and final Dreadnought-class ballistic missile submarine (SSBN). Both events occurred at BAE Systems’ Barrow-in-Furness shipyard in Cumbria—home to the UK’s only nuclear submarine manufacturing facility.
HMS Agamemnon Joins the Fleet
On September 30, 2025, HMS Agamemnon officially joined the Royal Navy fleet as the sixth of seven planned Astute-class submarines. The vessel was formally accepted into service following successful sea trials earlier in the year. The Astute class represents a generational leap over its Trafalgar-class predecessors in terms of stealth, endurance, and firepower. Each boat displaces around 7,400 tonnes submerged and is powered by a Rolls-Royce PWR2 pressurized water reactor that will not require refueling over its 25-year lifespan.
HMS Agamemnon is equipped with six 533 mm torpedo tubes capable of launching Spearfish heavyweight torpedoes and Tomahawk Block IV land-attack cruise missiles. The class also integrates Thales Sonar 2076—a fully integrated passive/active sonar suite considered among the most advanced in NATO service—and a state-of-the-art combat management system developed by BAE Systems.
The commissioning of HMS Agamemnon brings added operational flexibility to the Royal Navy’s undersea fleet amid increasing global maritime competition. According to First Sea Lord Admiral Sir Ben Key, “The arrival of Agamemnon strengthens our ability to project power beneath the waves and maintain persistent presence where needed.”
Construction Begins on Future HMS King George VI
Simultaneously with HMS Agamemnon’s commissioning ceremony was the steel-cutting event for Boat Four of the Dreadnought-class SSBN program—expected to be named HMS King George VI. This marks a critical milestone in Britain’s £31 billion program to replace its aging Vanguard-class submarines that currently carry the nation’s continuous at-sea nuclear deterrent under Operation Relentless.
The Dreadnought class is being developed jointly by BAE Systems Submarines and Rolls-Royce under contract from the UK Ministry of Defence (MoD). Each boat will displace approximately 17,200 tonnes submerged—making them among Britain’s largest warships ever—and will be powered by a new-generation PWR3 reactor derived from US naval reactor technology under US-UK cooperation agreements.
The four-boat class will carry Trident II D5 SLBMs launched from a Common Missile Compartment (CMC) co-developed with General Dynamics Electric Boat for interoperability with US Columbia-class SSBNs. The first boat in class—HMS Dreadnought—is expected to enter service in early-to-mid 2030s following extensive testing and sea trials.
Industrial Base Under Pressure but Delivering
BAE Systems’ Barrow shipyard remains central to both programs but faces significant industrial challenges. The concurrent build-out of Astute-7 (HMS Agincourt) alongside all four Dreadnought hulls has placed unprecedented demand on skilled labor, nuclear-certified facilities, and supply chains. To address this pressure, BAE has launched aggressive recruitment campaigns aiming to hire over 3,000 workers annually through apprenticeships and lateral hires across engineering disciplines.
A National Audit Office report from late 2024 warned that delays or cost overruns on either program could cascade into capability gaps for both conventional strike roles (SSNs) and strategic deterrence (SSBNs). However, MoD officials have reiterated their commitment to maintaining Continuous At-Sea Deterrence (CASD), which has been unbroken since April 1969.
Strategic Implications for NATO Maritime Posture
The dual progress on SSN and SSBN fleets reinforces Britain’s role as NATO’s leading European naval power with credible undersea capabilities. With growing Russian undersea activity in North Atlantic approaches—including suspected cable tapping operations—the need for modern hunter-killer submarines like Astute is acute. Meanwhile, sustaining CASD ensures London retains sovereign second-strike capability amid evolving threats from peer nuclear powers such as Russia or China.
The interoperability baked into both classes—via shared missile compartments or common sonar/weapon interfaces—also enhances allied integration. For example:
- Dreadnought’s CMC aligns with U.S. Columbia-class design for shared logistics/training pipelines;
- Astutes routinely deploy alongside U.S. carrier strike groups or conduct ISR missions in contested waters;
- NATO exercises increasingly include UK SSNs simulating adversary AIP/diesel-electric threats or engaging ASW forces.
Next Steps: Final Astute Boat & Dreadnought Testing Phase
The final Astute boat—HMS Agincourt—is currently undergoing systems integration ahead of sea trials expected in late-2026. Once delivered by ~2027–28 timeframe depending on dock availability and test results—it will complete one of Europe’s most advanced attack submarine classes.
Dreadnought Boat One is now structurally complete with initial reactor testing scheduled for mid-2026 before moving into harbor acceptance trials (HATs) followed by sea acceptance trials (SATs) around ~2030. Successive boats are expected every two years thereafter assuming no major delays emerge during integration or weapons qualification phases.
