Current Status of the Development and Operation of British Nuclear-Powered Submarines and Lessons for South Korea’s Nuclear Submarine Program: Policy Implications and Recommendations

Peter Ward

Research Fellow

Sejong Institute

1. Framing the Issue

As a middle power with a close alliance with the United States, the United Kingdom occupies a position that in some respects resembles that of South Korea. For that reason, the British experience carries important implications for Seoul, especially because the UK pursued its nuclear-powered submarine program on the basis of cooperation with Washington.

The key characteristics of Britain’s development and operation of nuclear-powered submarines can be summarized in four points: the Anglo-American special relationship, gradual technological self-reliance, the industrial and operational problems that emerged after the Cold War, and the diversification of operational areas and missions. Britain’s nuclear-powered submarine program began as an extension of the nuclear cooperation that the United Kingdom and the United States had built up during the Second World War. Through cooperation with the United States, Britain succeeded in reducing both development time and cost, but later strengthened its autonomy in reactor design and operation as well as in the management of its submarine force. After the end of the Cold War, however, structural constraints on submarine operations grew as procurement delays, maintenance backlogs, and rising decommissioning costs accumulated. At the same time, the operational geography of Britain’s nuclear submarine force has expanded from the eastern Atlantic to the Indo-Pacific, while its missions have broadened from undersea warfare to include land attack.

The origins of Britain’s nuclear submarine development closely followed the history of Anglo-American nuclear cooperation, and the pivotal step in that process was its institutionalization through the Mutual Defence Agreement (MDA). The MDA was the central mechanism that reduced the time and cost involved in Britain’s development of nuclear-powered submarines. The 1958 agreement provided the institutional basis for the transfer of classified information, research on military reactors, naval nuclear propulsion plants, and nuclear materials. Through revisions made after 1959, the agreement evolved from a framework for limited transfers into a standing cooperative system that included the exchange of nuclear materials and components. The transfer of propulsion technology and related information from the United States substantially reduced the burden Britain would otherwise have faced had it attempted to develop reactors and submarine systems entirely on its own. Anglo-American cooperation on nuclear submarines thus benefited not only Britain, but also the United States by supporting forward deployment and the maintenance of deterrence.

Anglo-American nuclear cooperation was not composed of treaties alone. It was institutionalized through a multilayered structure of consultative bodies and working-level organizations. High-level and senior-level consultations functioned as political and bureaucratic channels for reviewing the direction of cooperation and handling current issues. The establishment of Joint Working Groups institutionalized ongoing cooperation in detailed areas such as nuclear materials, manufacturing, accident response, computational methods, and classification systems. This institutionalization shows that Anglo-American nuclear cooperation was not a one-off transfer of technology, but a repeated and cumulative relationship.

AUKUS represents an extension of this established Anglo-American framework to Australia in the field of naval nuclear propulsion. The United States, the United Kingdom, and Australia had already used the Defence Trade Cooperation Treaty (DTCT) to avoid some of the friction and restrictions associated with general defense trade transfers, but separate agreements were still needed for the sharing of submarine reactor information. The AUKUS agreement turned some technologies that had previously been excluded into exceptions, thereby making naval nuclear propulsion cooperation under AUKUS possible. This shows that a civilian nuclear cooperation framework under a Section 123 agreement alone is not sufficient for military nuclear propulsion cooperation.

During the Cold War, Britain maintained a mixed submarine force structure, but after the Cold War it shifted to a reduced force centered on nuclear-powered submarines. Until the mid-1990s, the Royal Navy operated both diesel-electric submarines and nuclear submarines, but later retired its diesel boats and reorganized around a nuclear-powered fleet. The SSBN force maintained a four-boat structure and continued continuous at-sea deterrence (CASD), while SSNs remained the main platforms for undersea warfare and intelligence collection. Yet the overall number of submarines declined after the Cold War, and this reduction was accompanied by a weakening of the submarine industrial base and maintenance capacity.

The central problem facing the British nuclear submarine enterprise after the Cold War was the weakening of the industrial base across design, construction, maintenance, and decommissioning. Breaks in the accumulation of skilled labor and technical expertise created serious difficulties. The Astute class suffered construction delays and rising costs, and maintenance problems further reduced force availability. There is concern that the Dreadnought class and SSN-AUKUS could also be affected by these industrial and infrastructure bottlenecks.

The operational scope of British SSBNs and SSNs has also expanded. During the Cold War, operations were centered on the Atlantic, but in the post-Cold War period they have broadened across multiple domains and regions. SSBNs carried out continuous at-sea deterrence through the Resolution and Vanguard classes, and they continue to do so today under the burden of life extension. SSNs have long performed key North Atlantic missions including GIUK gap surveillance, tracking Russian submarines, protecting SSBNs, and conducting de-lousing operations. Since the 1990s, the addition of the Tomahawk Land Attack Missile (TLAM) has further expanded their mission set into land attack.

More recently, Britain’s nuclear submarine force has been recalibrated along two axes: responding to threats from Russia and expanding deployments into the Indo-Pacific. Britain is pursuing an Atlantic bastion strategy and strengthening cooperation with countries such as Norway in order to counter Russia’s underwater threat. At the same time, it has expanded SSN operations in the Indo-Pacific through carrier strike group escort missions, port visits to Australia, maintenance support at HMAS Stirling, and participation in Submarine Rotational Force-West (SRF-West).

The British case offers South Korea three policy implications. First, cooperation on military nuclear fuel and naval reactors cannot be achieved through a civilian agreement such as the existing U.S.-ROK nuclear agreement; it requires a separate arrangement. Second, the introduction of nuclear-powered submarines cannot be treated merely as a reactor development project. It must rest on a long-term industrial strategy encompassing design, construction, maintenance, and decommissioning. Third, South Korea’s concept of operations for nuclear submarines should not be limited to deterrence against North Korea. It should also include blue-water deployment, combined operations, and the protection of sea lanes. By designing the concept in this direction, South Korea can emphasize its potential contribution to U.S. blue-water operations and thereby improve the prospects for easier technology transfer from the United States.

2. The Development of Britain’s Nuclear-Powered Submarines

a. The Special Treaty Relationship with the United States and AUKUS

Britain’s nuclear cooperation with the United States was built on foundations laid during the Second World War. Britain’s Tube Alloys program made an important contribution to early nuclear weapons research in the United States, and under mutual agreement it was integrated into the Manhattan Project. British scientists participated in core areas such as implosion design.

After the war, the United States tightened its control over nuclear technology, but Anglo-American nuclear cooperation was not completely severed, and Britain still succeeded in establishing itself as an independent nuclear weapons state despite U.S. legal restrictions. The U.S. Congress became more concerned about the postwar spread of nuclear technology, and the Atomic Energy Act of 1946, the so-called McMahon Act, prohibited the transfer of military nuclear technology and related information. Even after the McMahon Act, Britain did not abandon its own nuclear weapons program. British leaders continued to insist that the country had to possess nuclear weapons. Britain conducted its first nuclear test in 1952 and its first hydrogen bomb test in 1957. These developments strengthened the case that Britain was a nuclear-armed ally suitable for renewed nuclear cooperation with the United States.

The conclusion and later revision of the Anglo-American Mutual Defence Agreement marked the institutional starting point for Britain’s nuclear-powered submarine program. Anglo-American cooperation on nuclear-powered submarines emerged in the context of growing anxiety over Soviet missile capabilities, especially the possibility that the Soviet Union might deploy intercontinental ballistic missiles ahead of the West. Beginning in 1956, plans were therefore pursued in earnest to forward-deploy Thor intermediate-range ballistic missiles in Britain and elsewhere in Europe.

The 1958 Mutual Defence Agreement allowed the transfer of a single nuclear propulsion unit, design drawings, and safety-related information. The 1959 revision went further, permitting the sale of non-nuclear components related to the submarine program as well as exchanges of nuclear materials. Britain provided plutonium, while the United States supplied uranium-235, tritium, and lithium. The agreement thus became the technical and material basis for Britain’s nuclear-powered submarine enterprise.

The 1958 agreement established the basic framework for nuclear defense cooperation between the United Kingdom and the United States. It allowed the two countries to exchange and transfer classified information, materials, and equipment insofar as these contributed to mutual defense and security. In particular, it created the institutional basis for cooperation in defense planning, training related to atomic weapons, assessments of enemy capabilities, research on military reactors, naval nuclear propulsion plants, and the supply and reprocessing of enriched uranium for submarine use. The agreement did not, however, permit the transfer of nuclear weapons themselves.

The most important development after 1958 was that what began as a limited agreement on information and propulsion cooperation became a renewable framework including transfers of nuclear materials, and was later restructured into a standing system centered on naval nuclear propulsion. With the addition of Article III bis in 1959, a legal basis was created for the transfer of special nuclear material and non-nuclear components, making much broader cooperation possible than under the original 1958 agreement. Because Article III bis included an expiration clause, repeated amendments were required after 1969 to preserve the effectiveness of this core material-transfer provision. From the 1980s onward, these renewals generally occurred at ten-year intervals.

This process involved more than simple extension. In 1980, language concerning end-use and security was revised. In 1985, the scope of enriched uranium transfers to Britain was broadened to encompass wider military purposes. The 2014 amendment substantially revised Article III for the first time, moving beyond the original 1958 structure of transferring one submarine propulsion plant and support for a limited period, and allowing the transfer of additional propulsion plants, parts, replacement cores, fuel elements, and related information. The 2024 amendment recast Article III as a broader provision for naval nuclear propulsion cooperation, deleted the sunset language in Article III bis, and eliminated the need for repeated extensions. As a result, the Mutual Defence Agreement became a more reciprocal and standing framework for cooperation.

The MDA was the key agreement that reduced the cost and time involved in Britain’s nuclear submarine program. It was concluded at the point when Britain was moving to develop its own nuclear-powered submarines, and it reduced the cost and time that would otherwise have been required had Britain tried to develop all of the core technologies independently. The transfer of propulsion technology and related information reportedly reduced British development time by at least three years and cut costs substantially. Cooperation also developed between Rolls-Royce and Westinghouse, and Britain was able to build the reactor for HMS Dreadnought and then modify and indigenize the design.

Anglo-American nuclear submarine cooperation also produced real strategic benefits for the United States. One representative case was the forward deployment of U.S. SSBNs to Holy Loch in Scotland from 1961 to 1992. Submarine Squadron Fourteen at one point consisted of as many as fourteen SSBNs and support ships. Holy Loch functioned as a maintenance and sustainment hub for the U.S. nuclear force during the Cold War and as a deterrent base directed at the Soviet Union. Cooperation with Britain thus underpinned America’s ability to forward deploy and maintain continuous deterrence.

The Mutual Defence Agreement and the 1963 Polaris Sales Agreement formed the institutional basis of Anglo-American nuclear cooperation, and that cooperation was reinforced through a range of mechanisms. At the highest level, senior consultations reviewed the overall direction of nuclear cooperation. Responsible officials on both sides met roughly every eighteen months to consider the long-term trajectory of cooperative projects and major issues. Below that, high-level consultations coordinated the day-to-day management of nuclear cooperation. Officials at the level immediately below the top leadership met every six to nine months to review progress and handle working-level problems. Administrative consultation mechanisms established procedures required for implementing the agreement, allowing the two countries to align the administrative rules and working procedures needed to carry it out.

The Joint Working Groups functioned as practical bodies for dividing and coordinating cooperative tasks among laboratories and relevant agencies. They met regularly, organized the division of labor, and used reciprocal visits to turn general cooperation into concrete projects. Through this system, practical cooperation was institutionalized across fields such as nuclear materials, warhead design, manufacturing, accident response, computational methods, and classification systems.

Exchange of Information by Visit and Report was an administrative mechanism through which atomic information could be exchanged in limited form through oral briefings and visual materials. Unlike the Joint Working Group system, however, it was not a permanent framework for continuous information exchange. Separate channels were also maintained to handle information related to particular projects or programs. In effect, these channels provided dedicated routes for information-sharing on specific cooperative efforts.

Even before AUKUS, and separate from the Mutual Defence Agreement, the Defence Trade Cooperation Treaty had already been concluded and ratified in order to minimize friction and restrictions in arms trade and defense technology transfer between the United States and the United Kingdom, as well as between the United States and Australia. Britain and Australia each concluded such treaties with the United States in 2007. These arrangements were designed to exempt certain transfers of defense articles and technology within the Approved Community from portions of the normal ITAR licensing process.

The treaty framework recognized ITAR exceptions for transfers, retransfers, and technology transfers within the Approved Community, but only within a limited scope defined by approved participants, approved end uses, and non-excluded items. Items or technologies on the Excluded Technology List remained subject to ordinary ITAR rules and licensing requirements. Even where excluded items were integrated into a larger system, separate approval requirements for the excluded item itself remained in force. Safeguards relating to the Non-Approved Community were also clear. Retransfer or re-export to foreign persons outside the Approved Community, use outside approved end uses, or changes in end use generally required prior written approval or separate authorization.

Even so, only through an agreement such as AUKUS could Australia be included in the sharing of submarine reactor information and related technology transfers between the United States and the United Kingdom. The earlier DTCT framework partially exempted certain transfers from ITAR licensing based on Approved Community and end-use criteria, but in practice its usefulness was limited. The later AUKUS exemption addressed this problem by introducing a mechanism that generally permits transfers between entities listed as Authorized End Users, rather than tying approval to specific end uses. This allows more flexible treatment than before, including for transfers involving complex systems that contain excluded items. In this sense, AUKUS extended the logic of Anglo-American nuclear cooperation into a trilateral setting.

It is also worth noting that Britain and Australia, like South Korea, each have a Section 123 agreement with the United States. However, cooperation on nuclear propulsion is not premised on Section 123 of the Atomic Energy Act of 1954. Section 123 applies only to non-military cooperation and therefore cannot provide the legal basis for AUKUS or any future cooperation on nuclear-powered submarines. Transfers of reactor designs, components, and nuclear fuel for Britain’s nuclear weapons and naval propulsion systems take place not under a Section 123 agreement, but under the Mutual Defence Agreement.

b. Technology Transfer and Fuel Sharing

1) Reactor Development

After the end of the initial phase of cooperation, Britain strengthened its autonomy in reactor design and operation. The initial phase of Anglo-American cooperation ended in 1963, after the British version of the S5W reactor had become operational. Britain’s first indigenous reactor, PWR1, entered service in 1965.

Britain introduced raft mounting inside the hull in order to reduce propulsion machinery noise. The United States was initially skeptical of this approach, but later adopted it. Development of the follow-on PWR2 began in the late 1970s, and the first reactor was completed in 1985. Whereas PWR1 required refueling every ten years, PWR2 could operate for roughly twenty-five to thirty years without refueling.

PWR1 was Britain’s first indigenous reactor plant and core, based on the U.S. Westinghouse S5W design. It was built by Rolls-Royce and deployed on the SSN HMS Valiant, entering service in 1966. PWR1 Core 1 was used in the Valiant-class SSNs and the Resolution-class SSBNs, which carried the Polaris strategic weapons system. PWR1 Core 2 was applied to the Churchill-class SSNs, while PWR1 Core 3 was applied to the Swiftsure-class and Trafalgar-class SSNs.

PWR2 was designed for the Vanguard-class SSBN, which replaced the Resolution class and operated the Trident strategic weapons system. Design work began in 1977, the first reactor was completed in 1985, and testing began in August 1987. PWR2 Core H was a core-for-life design intended to last for the life of the reactor, approximately twenty-five to thirty years, thereby eliminating the costly mid-life refueling process. It was applied to the Astute-class SSN and to the Vanguard-class SSBN during long overhauls and refueling periods.

The introduction of the next-generation PWR3 is part of this continuing line of Anglo-American reactor cooperation. PWR3 has been described as being based on a U.S. design and is often understood as linked to technology associated with the S9G reactor used in the U.S. Virginia class. This became possible through later revisions to the Mutual Defence Agreement, which permitted additional reactor technology transfer. Even so, actual reactor construction, including research, design, manufacturing, and support, continues to be handled by Rolls-Royce.

2) Fuel Procurement and Sharing

Britain procures civilian nuclear fuel through URENCO facilities located in the United Kingdom, but because treaty provisions restrict URENCO to civilian purposes, Britain secures military nuclear fuel through other means. The fuel supply issue illustrates the long-term sustainability of Britain’s naval nuclear propulsion system.

Fuel for these reactors has largely been supplied by the United States since 1962. Britain’s Capenhurst facility produced highly enriched uranium from 1954 to 1962, but was later converted into a low-enriched uranium production facility. The exact total amount of naval and warhead highly enriched uranium transferred by the United States to Britain has not been publicly disclosed, though estimates from the early 2000s put the figure at around fifteen tons. Britain’s naval use of highly enriched uranium is generally estimated at roughly 0.2 tons per year. Britain’s stock of fuel has been assessed as sufficient to meet all weapons-related requirements and between forty and sixty years of naval demand.

3.  Current Status of Operations and Strategy

a. Changes in Force Structure and the Emergence of Sustainment Problems

From the 1960s through the mid-1990s, Britain maintained a mixed submarine force of diesel-electric and nuclear-powered boats. Diesel submarines operated in waters near Britain and in the eastern Atlantic from 1908 to 1994, and they played an important role in anti-submarine operations during both world wars. From the 1970s onward, Britain adopted a policy of maintaining four ballistic missile submarines in order to preserve a continuous at-sea nuclear deterrent.

The first SSBN, the Resolution class, saw all four boats enter service within six years of the start of construction. Under the 1963 Polaris Sales Agreement, Britain acquired the Polaris submarine-launched ballistic missile. The four Resolution-class boats entered service between 1967 and 1969 and were all retired between 1992 and 1996. By adapting the already designed Valiant-class SSN, Britain was able to compress development time. At that stage, Britain also still possessed the shipbuilding capacity needed to support such a program.

After 1992, however, the early retirement of diesel submarines and the reduction in the number of nuclear-powered submarines together produced a trend toward quantitative decline in force structure. Britain’s diesel submarines had played a supporting role in coastal anti-submarine warfare and surveillance of the GIUK gap, but after the end of the Cold War and the collapse of the Soviet Union, their utility was judged to have declined. Cost was one issue, but these boats had also made some contribution to sustaining the ecosystem for submarine design and shipbuilding. The Upholder class, Britain’s last diesel-electric submarine class, was selected for early retirement under the 1993 defence review and later became the Victoria class now operated by the Royal Canadian Navy. With the retirement of diesel boats and the slow pace of SSBN construction, Britain’s submarine force shrank by more than half between 1980 and 1997.

After the Cold War, and amid changes in the structure of weapons procurement, procurement problems became severe. As the Astute program showed, cost control became difficult because, unlike in earlier periods, the Ministry of Defence did not serve as the prime contractor leading the basic design and providing facilities to the shipyard. The long gap between the design of the Vanguard class and the Astute class made it very difficult to maintain technical continuity, and program costs rose sharply.

Post-Cold War industrial restructuring and the sharp decline in manpower undermined maintenance performance and shipbuilding capacity, and there is concern that this will also have a negative effect on AUKUS. The current maintenance problems affecting the Astute class are serious, and it has been noted that only one of the five boats is fully available for operations. The main issue is said to be obsolete infrastructure. The next-generation SSBN, the Dreadnought class, was originally expected to enter service much earlier, but entry into service has been delayed into the 2030s. SSN-AUKUS will be based on Britain’s design and construction infrastructure, but that infrastructure is already heavily committed to the Dreadnought class. In this context, the difference in submarine construction timelines between the United Kingdom and the United States is also striking.

Britain’s military nuclear propulsion and nuclear weapons programs are closely intertwined with the civilian nuclear energy sector and are marked by strong interdependence and cross-subsidization. Major firms such as Rolls-Royce have argued that without small modular reactor projects and new nuclear construction, it would be difficult to maintain military reactor capabilities. In other words, sustaining and strengthening the industrial base in terms of technical expertise and manpower requires a continuing pipeline of related projects.

The cost and backlog associated with dismantling retired nuclear submarines have also become serious. A large number of retired nuclear submarines remain undismantled, and the estimated total cost of decommissioning over a one-hundred-year period is extremely high. As in the United States, this appears to reflect the combined effects of aging infrastructure and manpower shortages. At the same time, the budget required simply to preserve the condition of retired but not yet dismantled submarines is relatively modest, and much of the structure and equipment of retired nuclear submarines is thought to be reusable or recyclable.

Despite these difficulties, the Astute class is still widely regarded as an excellent nuclear submarine. Its stealth characteristics are often assessed as comparable to, or in some respects better than, those of the U.S. Virginia class. In cost terms, the United States benefits from economies of scale and shorter construction timelines, but the Astute class also has the advantage of a lower overall price.

In order to reduce cost growth and delays, Britain has also moved toward integrating the procurement, support, and decommissioning systems for nuclear submarines and managing them as a national enterprise. Accordingly, the Submarine Delivery Agency was established in 2018 and now oversees procurement and support across the full life cycle of Britain’s submarine force.

b. Changes in Operational Areas and Roles

From the Cold War onward, Britain has maintained continuous at-sea nuclear deterrence through its nuclear-powered submarines. With the entry into service of the Resolution class, Polaris-armed submarines were deployed. Because Polaris lacked multiple warheads, however, Britain chose not simply to adopt Poseidon in the same way as the United States, but instead upgraded Polaris through the Chevaline program in cooperation with Washington in order to improve its penetrability. After the retirement of the RAF’s WE.177 warhead in 1998, Britain’s strategic and tactical nuclear capability has in practice been sustained solely through its SSBN force.

At present, continuous at-sea deterrence faces significant strain. The Vanguard class, the SSBN force currently in service, began operations in 1993. Although its original service life was twenty-five years, delays in replacing it with the Dreadnought class mean that it may need to remain in service for as long as forty years. Patrol lengths have also grown dramatically, and some submarines are known to require maintenance periods of more than seven years. These trends indicate the increasing burden being placed on the current deterrent fleet.

Since the 1980s, Britain’s SSN force has continued to conduct intelligence collection and potential strike operations focused on the eastern Atlantic. Until the 1970s, their role centered on escorting the sea lines of communication needed to transport U.S. land forces to Europe, but this role was later adjusted in light of the limited deployment range of Soviet undersea forces. In the GIUK gap, British SSNs tracked Russian submarines and monitored the route to ensure that they could not pass through undetected, while also interacting with wider detection networks.

In order to block threats seeking to track and detect Britain’s continuous at-sea deterrent force, SSNs conduct de-lousing operations, checking whether Russian or formerly Soviet nuclear submarines are present near home waters during force deployment and attempting to disrupt efforts to detect British SSBNs. They also conduct tracking and detection missions against Russian SSBNs in the Norwegian Sea and are operated in such a way that they could attack Russian SSBNs in wartime.

Since the Russia-Ukraine war, the modernization of the Russian Navy and the growing underwater threat in the Arctic and eastern Atlantic have reinforced naval cooperation among like-minded states. Russia has deployed some of its most advanced submarines with the Northern Fleet, and additional deployments are expected in the future. The emergence of further next-generation Russian submarines is likely to make the tracking of Russian undersea forces even more difficult.

In response, Britain has adopted an Atlantic bastion strategy. This strategy aims to restrict the expansion of Russian surface and undersea operating areas through a combination of underwater sensor networks, nuclear submarines, and unmanned underwater systems. At the same time, Britain has strengthened defense cooperation with Norway and other regional partners, and its SSN force also plays a role in the framework of the Joint Expeditionary Force.

Since the end of the Cold War, nuclear-powered submarines have also acquired an additional land-attack role. Britain introduced the Tomahawk Land Attack Missile, and after initial testing it was deployed aboard British SSNs and used in operations alongside the United States and NATO in Yugoslavia, Afghanistan, Iraq, and Libya. Unlike a conventional submarine-launched ballistic missile, TLAM is launched through a torpedo tube rather than vertically, which helps preserve the submarine’s stealth. Britain is now moving toward newer versions with greater range.

More recently, under AUKUS and the Indo-Pacific Tilt policy, the operational scope of British SSNs has widened further, though their carrier strike group escort role remains intact. During Britain’s Indo-Pacific carrier strike group deployment, a British SSN visited Australia, and later operations again confirmed the geographic spread of British submarine activity from the Mediterranean to Australia. Maintenance support at HMAS Stirling and the planned rotational deployment of British nuclear-powered submarines through Submarine Rotational Force-West indicate that the Indo-Pacific is becoming an increasingly important theater for British SSN operations.

Britain’s recent strategic thinking presents strategic stability as a central task involving the prevention of miscalculation and error and the maintenance of a credible allied military posture. In that framework, AUKUS is understood as one of the main pillars for achieving that objective. Britain believes that through AUKUS it can strengthen its SSN force, industrial base, and combined operational capability at the same time, thereby reinforcing both strategic stability and deterrence.​