Rolls-Royce Submarines is expanding its reactor production and workforce to support the Royal Navy’s next generation of nuclear submarines and the AUKUS partnership. This technical briefing outlines the evolution of UK naval reactor design, the company’s central role, and the growing industrial effort at Raynesway.
Transatlantic partnership
The British nuclear submarine programme began with significant assistance from the United States under the 1958 US–UK Mutual Defence Agreement. The RN’s first nuclear-powered boat was equipped with a US-designed S5W Pressurised Water Reactor (PWR) supplied with associated training, technical data and support. This arrangement allowed the UK to enter the nuclear propulsion era rapidly, with the construction of HMS Dreadnought (XII) commissioned in 1963. Proving the RN could operate this technology was foundational to the subsequent establishment of the submarine-based nuclear deterrent based on the Resolution class SSBNs and the US-supplied Polaris missile system.
The agreements with the US are conditional on maintaining very high classification levels; details of nuclear propulsion technology are extremely sensitive and highly guarded. The AUKUS pact requires an unprecedented level of information sharing with the Australians and is a challenge to submariners, companies and organisations with a deeply embedded culture of secrecy.
Although the initial plant was American, it provided the foundation for what is now a sovereign UK capability. The PWR1 reactor, derived from the US design, equipped the Resolution, Valiant, Churchill, Swiftsure and Trafalgar-class boats. Over time, the UK developed its own expertise, moving from adaptation to independent design authority while maintaining a close technical relationship with the US Naval Nuclear Propulsion Program.
Since the 1960s, more than 30 reactor plants and around 90 cores have been produced by Rolls-Royce in the UK. Collectively, RN nuclear-powered submarines have safely travelled over 18 million miles using these systems. This long operational history has underpinned deep experience in reactor integration, safety, and lifecycle management.
The next major step came with the PWR2 reactor, fitted to the Vanguard and Astute classes. Designed to avoid mid-life refuelling, PWR2 represented a shift towards longer core life. The current generation PWR3, developed for the Dreadnought-class, introduces improved passive safety features, enhanced shock resistance and greater use of advanced manufacturing techniques.
Rolls-Royce at the core
Rolls-Royce Submarines Limited (RRSL) has been central to the UK’s naval nuclear propulsion programme since its inception in the 1950s and remains the design authority for the RN’s reactor plants. Its Submarines business operates two nuclear licensed sites at Raynesway in Derby: the Neptune reactor site and the Nuclear Fuel Production Plant (NFPP). The Neptune reactor serves as a testbed while NFPP handles the Highly Enriched Uranium (HEU) fuel and assembles the core that is placed inside the Reactor Pressure Vessel.
RRSL is responsible for delivering Nuclear Steam Raising Plants (NSRP), the complete reactor systems that generate steam for submarine propulsion. This includes reactor cores, primary circuit pipework and valves, major pressure vessels and electronic control systems. Rolls-Royce also produces elements of the secondary propulsion system, including turbo-generators and propulsors.
The propulsor assembly, also made by RRSL, is among the most sensitive components of a submarine. It includes the tail shaft, bearings, rotor, and stator enclosed in a shroud made from composite materials, all engineered to extremely fine tolerances. The rotor blades require highly specialised machining to ensure they are the correct shape and have flawless surfaces, which could otherwise create turbulence. The propulsor must drive the submarine to speeds exceeding 30 knots while minimising noise and cavitation, critical for acoustic stealth.
Beyond manufacture, RRSL also manages these systems across their full lifecycle. This includes design assurance, safety case substantiation and in-service support for the Vanguard and Astute classes. Support is provided globally through an operations centre in Derby and extends to activity at Barrow, Devonport and Faslane. RRSL is involved in the Submarine Maintenance Recovery Plan (SMRP) initiated by the First Sea Lord in January to tackle the poor availability levels achieved by the Astute-class boats.
The UK retains sovereign design authority for its reactor plants, but the relationship with the United States remains important. Collaboration continues in areas such as reactor longevity, quieting and support arrangements, with PWR3 understood to have benefited from sharing of US design philosophy around simplified and safer reactor architectures. The amount of commonality with modern USN reactors and the actual level of industrial cooperation is not in the public domain.
Towards SSN-A
Current RR production activity spans multiple programmes. Final reactor deliveries for the Astute class are ongoing, while final PWR3 units are in production for the Dreadnought-class SSBNs. At the time of writing, HMS Dreadnought is nearing structural completion in the Devonshire Dock Hall at Barrow.
The PWR3+ reactor, intended for SSN-A, passed its Critical Design Review in late 2025, establishing a baseline for further optimisation. While information is limited, the PWR3 ‘plus’ is understood to be an evolution of PWR3, incorporating refinements to improve manufacturability and integrate new technologies.
Reactors for seven boats are at various stages of manufacture in Derby, reflecting long-lead work aligned with both UK and Australian requirements. On paper, at least, SSN-A will be a 20-boat programme, with the UK aspiring for up to 12 boats and Australia planning to acquire 8, although these numbers may prove optimistic. The allocation of reactors for each nation will be a decision for the customer to be agreed at a national level.
All reactor plants for the AUKUS attack submarine programme will be manufactured in the UK at Raynesway. While Australia will construct its submarines domestically, the reactors will be shipped out from the UK, presenting complex logistical and security considerations. This may involve either building or modifying an existing ship to meet the exacting transport requirements. The first SSN-A will be delivered to the RN in the late 2030s and the first Australian boat should be in service in the 2040s.
Expanding Raynesway
To meet rising demand, RRSL is undertaking a major project to enlarge its Derby facility, roughly doubling its footprint. Announced in 2023 and funded by the MoD and Australia, the development is intended to support a higher tempo of submarine production driven by both national requirements and AUKUS commitments.
A central element of this effort is workforce growth. The Submarines business has expanded to around 5,500 personnel, an increase of approximately 2,000 over two years. Recruitment has drawn on experienced engineers, career changers and former submariners, supported by a strong employer reputation and the long-term stability of the nuclear enterprise.
The Nuclear Skills Academy, established in 2022, provides a structured pipeline for new entrants. Around 800 apprentices are currently in training, with fully qualified engineers expected to emerge after four years. This approach is designed to address demographic pressures while preserving critical knowledge through transfer from experienced staff. Training and recruitment are not confined to Derby. Satellite sites in Glasgow and Cardiff have been established to broaden access to talent, recognising that the required skills base is geographically dispersed. International collaboration is also shaping the workforce strategy. Australian personnel have already begun training with RR in the UK and there are plans to develop a sovereign skills base in Australia using a similar model.
The expansion reflects a broader shift towards dual production lines capable of supporting both UK and export submarine programmes. While some roles require highly specialised nuclear qualifications, many positions can be filled through retraining from adjacent sectors, widening the available talent pool.
The UK’s Defence Nuclear Enterprise stands out for its long-term funding and planning stability, allowing sustained investment in infrastructure and skills. This continuity provides RRSL with a predictable pipeline of work extending decades into the future, underpinning the industrial capacity required to deliver the next generation of RN and RAN submarines.
