Blue water submarines: capabilities and requirements

Despite the ever-increasing number of navies harbouring ‘blue water’ naval ambitions, the total of those with the means to field this capability underwater is limited. The nuclear-powered submarine’s combination of speed and endurance continues to provide an unrivalled capacity to undertake long-range, oceanic deployment. However, few nations have either the technological base or financial resources to acquire such vessels. As a result, the acquisition of long-range diesel-electric boats remains the default option for many of these fleets. This article examines the major programmes that are currently underway for both submarine types.

Blue water submarine capabilities

Although precise definitions of a ‘blue water’ navy differ, most commentators agree that the capacity to deploy and sustain naval power at distance across the world’s oceans lies at the term’s heart. In the underwater domain, this capability is closely associated with a submarine that can transit at high speed across long distances to the desired operational area. Here, it has to be capable of sustaining its mission for a considerable period; a requirement that inevitably has significant implications in areas such as endurance, habitability and the amount of weaponry that needs to be carried.

The conduct of oceanic underwater operations is not new in naval warfare. The Kriegsmarine’s U-boat offensive during the Battle of the Atlantic and the US Navy’s devastating submarine campaign against Japanese shipping in the Pacific are good examples of strategic campaigns carried out by submersibles operating at distance from their home bases. However, such offensive potential has been a secondary consideration for many past and current submarine operators, whose primary focus has been built around a more defensive mindset that emphasises deployments closer to home. Whilst the current generation of modern diesel-electric boats – often equipped with air independent propulsion (AIP) – are well-suited for such missions, they typically lack the speed and size optimal for operations at longer range.

Given this backdrop, it is unsurprising that the major navies configured largely for expeditionary warfare have tended to focus on the nuclear-powered attack submarine (SSN) as the centrepiece of their underwater fleets. The US Navy quickly reached the conclusion that the qualities of nuclear-propelled craft were so far in advance of diesel-electric alternatives for their chosen missions requirements that they should dispense entirely with the latter, a decision subsequently followed by the United Kingdom and France. Meanwhile, both Russia and China operate a mixture of nuclear-powered and diesel-electric boats. Notably, this virtual monopoly of nuclear-powered submarine operators corresponds with the five permanent members of the UN Security Council in a reflection of the financial, political and technical hurdles that all need to be overcome to acquire the type.

Existing operators

The US Navy is the largest operator of SSNs today, with around 50 of the type in service as of early 2024. Current construction is dominated by the Virginia (SSN-774) class. This was initially developed after the end of the Cold War as a more cost-effective alternative to the previous Seawolf (SSN-21) design. A total of 22 of the class had been commissioned between 2004 and the end of 2023, with a further 16 authorised to date. The boats are powered by a SG9 reactor that utilises highly enriched uranium and is intended to serve throughout a vessel’s life without the need for refuelling. The Virginias have been procured in various ‘Blocks’ and have benefitted from progressive improvement. Assembly is shared between General Dynamics Electric Boat at Groton in Connecticut and Huntington Ingalls Industries at Newport News in Virginia.

Increased tensions in the Asia-Pacific region mean that submarine procurement is a high priority for the US Navy, which is also experiencing downwards pressure on force numbers as the remaining Cold War-era attack submarines decommission. There is also a need to increase weapons-carrying capacity given that the four Ohio class strategic submarines which were reconfigured as cruise missile-carrying boats (SSGNs) also face imminent retirement. This requirement is being met by the insertion of a Virginia Payload Module (VPM) – a 25.6 m (84 ft) hull plug – in most of the boats procured from Block V onwards. Each VPM contains four large diameter vertical launch tubes that can carry 28 Tomahawk cruise missiles, increasing total payload in the order of 75%. Current acquisition cost of a Virginia class submarine equipped with a VPM is in the region of USD 4.4 Bn (EUR 4.1 Bn) per boat.

Despite some problems ramping up production of Virginia class boats to a sustained level of two units each year, the tried and tested design is well-suited to the US Navy’s requirements as it attempts to stabilise and then expand SSN numbers to at least 60 vessels over the next 30 years. It should be noted that the official target for US Navy attack submarine numbers is 66 but various alternative force structures are under consideration. Current plans therefore envisage continued construction of the class until the mid-2030s when procurement of a replacement SSN(X) design will commence. Early US Navy pronouncements suggest that this new class will be configured to “…provide greater speed, enhanced horizontal payload capacity, improved acoustic superiority and higher operational availability…” than existing boats.

Turning to Europe, the British Royal Navy is currently well-advanced with renewing its SSN flotilla with its Astute class design. Also a product of the immediate Cold War era, delivery of these new boats was badly impacted by the erosion of the defence industrial base that accompanied this new environment. However, five out of a planned total of seven vessels are now in service and construction of the remaining pair by BAE systems at Barrow-in-Furness is well advanced. HMS Astute is broadly similar in size and concept to the Virginia class’s original configuration, utilising a PWR2 reactor that also has a ‘full life’ core. However, the British submarines lack the vertical launch capability of their American counterparts, utilising conventional torpedo tubes to deploy their cruise missiles. Work is now underway on the follow-on SSN-A design, which will commence deliveries in the late 2030s as part of the AUKUS programme (see further below).

The French equivalents of the British Astutes are the Suffren class, of the ‘Barracuda class’ design. The first unit of a planned six-strong class commenced construction at Naval Group’s Cherbourg facility in December 2007 and became operational in mid-2022. A sister, FS Duguay-Trouin, was delivered in July 2023 and the remaining boats are at various stages of construction for delivery through to the end of the decade. Although intended to perform similar duties to the American and British SSNs, the French boats are considerably smaller and have a reduced weapons load-out in consequence. This compromise may reflect the importance of the confined waters of the Mediterranean to French operational requirements. Another important difference is the use of low enriched uranium in the class’s K15 reactors. Whilst necessitating refuelling every ten years, this provides valuable synergies with France’s strong civilian nuclear sector. The Suffren class are also notable through being capable of operating in stealthy turbo-electric drive; a capacity that is of growing importance as anti-submarine warfare detection capabilities continue to advance.

Russian naval forces were badly downgraded in the Cold War’s aftermath, but the fleet’s underwater capabilities have always been accorded a relatively high priority. In addition to playing an important role in nuclear deterrence, submarines have played an important role countering the ‘West’s’ superiority in carrier aviation and surface combatants. After a period of considerable disruption, blue water requirements are now being met by series production of the Project 885M or ‘Yasen M’ class by the United Shipbuilding Company’s Sevmash subsidiary at Severodvinsk in Northern Russia. Derived from the sole Project 885 boat RFS Severodvinsk, the ‘Yasen M’ design is generally classified as a nuclear-powered cruise missile submarine (SSGN). It has many conceptual similarities with the VPM-equipped Virginias but its ability to deploy 3M22 ‘Tsirkon’ hypersonic cruise missiles provides a capability currently absent from NATO equivalents. Three ‘Yasen M’ series submarines have been commissioned to date and a further five are under construction. Open source information suggests that a total of between 10 and 12 Project 885/885M boats is ultimately envisaged.

Although China had deployed SSNs since the 1970s, it has only been since the emergence of the People’s Liberation Army Navy’s (PLAN’s) blue water ambitions in the current millennium that the type has gained its present importance. Even now, the series of current Type 093 boats are believed to lag behind foreign contemporaries in key areas such as acoustic stealth. Perhaps in consequence, they are only being built in limited numbers by Bohai Shipbuilding Heavy Industry at Huludao. The yard delivered two Type 093 and four Type 093A class submarines from 2006 onwards and is now outfitting at least two improved Type 093B variants. Whilst firm details are scarce, it has been widely reported that the design benefits from Russian technology acquired after the Cold War came to an end. If the previous trajectory of Chinese surface combatant construction can be relied upon, it would seem that the Project 093 class submarines are essentially prototypes for an improved design that is often referred to as the Project 095. This is due to enter rapid series production once developmental work is concluded.

Blue water aspirants

In addition to existing operators, the expansion of navies developing blue water capabilities means that there are a growing number of aspirants to the exclusive ‘SSN club’. Of these, only India currently has actual experience of operating nuclear-powered attack submarines, having leased Russian-built Project 670 and Project 971 class boats in the past. At the current time, its only operational nuclear-powered boat is the highly secret INS Arihant, lead unit of a class of four planned strategic submarines. There are longer term ambitions to field a flotilla of six Project 75 Alpha SSNs that, like the strategic boats, would be built at the Naval Shipbuilding Centre at Visakhapatnam. Although preliminary clearance for the programme was granted in 2015, it is likely to be well over a decade before the new class enters service. In the interim, it has been reported that India will lease another Russian Project 971 class boat to increase its experience of SSN operations.

Brazil is another country with longstanding ambitions to operate SSNs. However, its rationale for acquiring the type is somewhat different than for other operators focused on blue water power projection. The Brazilian Navy’s own requirement is driven more by a desire to safeguard the extensive waters of its exclusive economic zone (often referred to as the ‘Blue Amazon’), a mission for which the speed and endurance of nuclear-powered units are well-suited. Work to develop a SSN commenced as early as the 1970s but it is only in recent years that this has gained traction.

The Brazilian Navy’s current plans are focused on combining its long-term research into developing an indigenous nuclear reactor with the broader submarine technology transferred from France as part of local construction of the diesel-electric ‘Scorpène’ design under the huge ‘PROSUB’ submarine development programme. This approach leverages the substantial investment made in the infrastructure to build and support submarines at the vast Itaguaí industrial complex west of Rio de Janeiro developed with the assistance of Naval Group following signature of a series of contracts in 2009. The facility has already delivered two of a quartet of ‘Scorpènes’ and will progressively transition to the construction of the planned SN-BR. Fabrication of a test section of the new boat, to be named Álvaro Alberto in honour of the father of the navy’s nuclear programme, commenced in October 2023. It is hoped that she will eventually be delivered in the early 2030s as the prototype of an extended class.

The most recent country to embark on SSN acquisition is Australia. It plans to acquire a flotilla of nuclear-powered submarines under the trilateral AUKUS security partnership with the United Kingdom and United States that was announced in September 2021. The procurement owes much to the country’s desire to be able to deploy submarines to counter Chinese naval expansion in South East Asia; a requirement that emphasises speed and endurance. It was previously intended that procurement of large, diesel-electric submarines derived from France’s Suffren class would provide this capability. However, the attractions of nuclear propulsion ultimately became irresistible as the cost/capability balance of the resultant ‘Shortfin Barracuda’ or Attack class programme started to look increasingly unattractive.

Current Australian plans envisage a phased transition to SSN operation under which increased deployments of British Royal Navy and US Navy submarines to Australia and an associated ramp-up in training will be followed by transfers of Virginia class submarines from the latter’s inventory. This will ultimately pave the way for introduction of a class of new AUKUS (SSN-A) nuclear-powered attack submarines that will be developed for Australia and the United Kingdom under a joint programme that will also benefit from the input of US technology. Deliveries of the Australian submarines will commence in the early 2040s after assembly at the Osborne Naval Shipyard in Adelaide, South Australia utilising PWR-3 reactors produced by Rolls-Royce in Derby, United Kingdom. The ability of American and British industry to produce whole-life reactor cores is seemingly an important enabler of the Australian programme, enhancing the security of nuclear material in compliance with the requirements of the international nuclear non-proliferation regime.

The conventional alternative

Although Australia’s experience is indicative of the superiority of nuclear propulsion for blue water submarine deployments, the hurdles that need to be overcome to acquire this capacity are substantial. In addition to the considerable expense involved in procuring and operating SSNs, the technological and political obstacles to adopting nuclear propulsion are also significant. Indeed, the AUKUS programme is the first occasion on which a non-nuclear weapons state has acquired nuclear reactors to power submarines. As such, the acquisition of large, diesel-electric submarines remains the only practical option for many fleets wishing to expand their expeditionary underwater capabilities.

Within Europe, the best example of a modern, conventionally-powered ‘blue water’ submarine is probably Spain’s new S-80 Isaac Peral class. The lead boat was commissioned in November 2023 after a protracted construction period resulting from the original design turning out to be overweight. Three additional boats are currently under construction at Navantia’s Cartagena shipyard. The design is based on staff requirements that emphasised global naval power projection both across the oceans and into the littoral. The latter mission set is reflected in an ability to deploy land attack cruise missiles and the specification of an advanced AIP plant incorporating bioethanol reformer-based technology. It should be noted that the first two boats will be fitted ‘for but not with’ this capability. The design is relatively unusual as a large, diesel-electric submarine suitable for extended deployment. This could make it an attractive proposition for other navies seeking this capability.

The Royal Netherlands Navy’s longstanding requirement to replace its existing Walrus class with submarines capable of extended deployment has revealed other potential options. The Dutch Ministry of Defence (MoD) considered three proposals from:

• Naval Group: A diesel-electric variant of the nuclear-powered ‘Barracuda’ class broadly similar in concept to the ‘Shortfin Barracuda’ previously offered to Australia.
• Saab (in partnership with Damen): A C718 variant of Saab’s C71 expeditionary submarine concept, itself derived from Sweden’s A26 Blekinge
• thyssenkrupp Marine Systems: A stretched expeditionary (‘E’) variant of the new Type 212CD design that has already been ordered by Germany and Norway.

All these boats have a submerged displacement in excess of 3,000 tonnes, offering extended range and a significant weapons-carrying capacity. On 15 March 2024, the Dutch MoD announced their decision, selecting Naval Group’s diesel-electric Barracuda design.

Beyond Europe, the demands of operations over the vast extent of the Pacific have driven the adoption of large diesel-electric submarines by a number of navies across the region. Australia’s existing Swedish designed Collins class were an early example of this trend, but it is the Japan Maritime Self-Defence Force (JMSDF) that has greatest experience of developing the type. Its latest Taigei (SS-513) class are large vessels with a submerged displacement of over 4,000 tonnes. Construction is shared between Kawasaki Heavy Industries and Mitsubishi Heavy Industries at the two companies’ shipyards in Kobe. An interesting innovation is their use of Lithium-ion batteries, which were first introduced in the final members of the preceding, Soryu (SS-501) class. Their higher energy density compared to many other battery types potentially offers the ability for greater sustained speeds, bridging some of the gap with nuclear-powered boats. It has also been reported that the JMSDF’s next submarine class will incorporate vertical launch systems for use with the Tomahawk cruise missiles, which the country is in the course of acquiring.

Developments in Japan are being closely mirrored by those in neighbouring South Korea. The initial batch of three submarines completed to its latest KSS-III design by Hanwha Ocean at Okpo and Hyundai Heavy Industries in Ulsan incorporates vertical launch cells for submarine-launched ballistic missiles. A second batch will also be equipped with lithium-ion batteries for greater underwater endurance and speed. Together, this combination provides significant capabilities to support the Republic of Korea’s growing blue water naval ambitions, which also extend to aircraft carrier acquisition. However, the class’s primary function is seemingly to act as part of the country’s ‘Three Axis’ deterrent against potential North Korean aggression, providing the means of undertaking a powerful conventional response to any nuclear strike.

The future

Whilst the capacity of nuclear-powered submarines to sustain blue water operations remains unchallenged, it seems likely that the numbers of fleets adopting this type will remain limited. Only six navies have operated SSNs in the seventy years since the first, USS Nautilus (SSN-571), was commissioned on 30 September 1954 and only one or two additions are likely in the decades ahead. Whilst developments in the field of diesel-electric submarine technology will likely narrow the performance gap with their nuclear counterparts, operators of the ‘true’ blue water submarine will remain an exclusive club for the foreseeable future.

Conrad Waters is Editor of Seaforth World Naval Review, Joint Editor of Maritime Defence Monitor and a regular contributor to other Mittler Report publications.