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The Royal Navy’s undersea capabilities: Deep enough?

Around 90% of the world’s goods move by sea. 70% of the world’s surface is water, 64% of which is unregulated – the high seas – allowing freedom of movement of goods and the navies protecting them. In other words, this is not a maritime century, it is a maritime world, and survival depends on the movement of goods, information and energy both above and below the waves.

If only it were that simple. Humans live on land and associate themselves with it more readily as a result. The land thus has a public relations advantage over its out-of-sight sibling. Nevertheless, if security and prosperity are the first priority of any democratic government, then it is clear that as global temperatures rise, both literally and geopolitically, the requirement to exploit and protect maritime resources will go up in lockstep.

The purpose of undersea capabilities

Specifically, what are the United Kingdom’s (UK) undersea capabilities for? Their purpose can be grouped into four buckets: to distribute, deter, detect and defeat

Protecting undersea distribution has two components: information and energy. Transatlantic financial information exchanges to the tune of US$10 trillion (£7.6 trillion) a day are the almost exclusive preserve of over half a million miles of fibre optic cables. The trade of energy between the UK and Ireland, France, Norway, Belgium, and the Netherlands is also facilitated predominantly via undersea cables. To be sure, there is redundancy baked into the 213 separate systems, but there are also well-publicised chokepoints and therefore vulnerabilities. It is no exaggeration to say the way of life of many depends on these cables.

Map 1: Underwater cables in the Euro-Atlantic region

It is not just undersea information and energy which must be protected. On the sea, commercial shipping, ports and their infrastructure, chokepoints and economic exclusion zones all need protection if countries are to trade goods safely and without fear of disruption. Britain itself also needs to be secure from the actions of state-based adversaries. Here, the purpose of navies as a deterrent emerges; undersea, the Royal Navy’s continuous at-sea deterrent, on patrol every day without fail since 1969, provides the UK with a guaranteed nuclear second strike capability with which to deter other nuclear-armed states from threatening British interests. Elite Royal Navy capabilities, particularly nuclear-propelled attack submarines (SSNs) armed with long-throw cruise missiles, also provide a potent conventional deterrent.

To detect and defeat are the final pieces of the Royal Navy’s undersea capabilities jigsaw. However, the Royal Navy does not do this alone. A vast web of allied and organic sensors including intelligence networks, satellites, undersea sensors, remotely-crewed submersibles, maritime patrol aircraft, frigates and their helicopters, and SSNs, all communicating across an intricate (and not always compatible) array of classified systems is required. And these networks are not iPhones – they need constant liaison and practice to work.

Britain’s undersea rivals

In terms of the UK’s undersea efforts over the last decade, combatting Russian and Iranian activity has been the main priority. Efforts to counter Russia largely have been in the High North, North Atlantic and latterly the Mediterranean. And for good reason: the Russians have a well-funded directorate called the Main Directorate for Deep Sea Research (GUGI), dedicated to ‘gathering intelligence or to work with installations on the seabed including sabotage.’ Between this and some of the Russian Navy’s SSNs, Russia possesses sophisticated undersea equipment which can operate decisively if required. 

Deterring and detecting (and occasionally defeating) Iranian undersea activity is relatively new compared to that of Russia but has become a mainstay of naval activity since the onset of the Royal Navy’s Armilla patrols in the 1980s. Early on, much of this was focused on Iran’s mine-laying capability in the Strait of Hormuz as an attempt to threaten maritime traffic. More recently, Iran has developed the use of fast-attack craft to shepherd escaping warships into a pre-laid mine pattern. Iranian anti-submarine activity is much less sophisticated than its Russian counterparts, with only a handful of ageing diesel submarines which are limited in both range and depth in operation. Of greater concern is the Yono, a stealthy mini-submarine which can hover for days at a time in places like the Strait of Hormuz, ready for a high-value unit such as an aircraft carrier to pass and the order to fire its two heavyweight torpedoes at it. In a fight with Iran, any Yono class in ports would be quickly destroyed, while any at sea would be a menace.

With Russia and Iran embedded firmly in the Royal Navy’s recent psychology, what about the People’s Republic of China? Although the capabilities of the People’s Liberation Army Navy (PLAN) do not threaten Britain directly in Euro-Atlantic presently, the PLAN’s rapid expansion and the continued modernisation of its undersea capabilities – which will soon see it present a considerable threat in the Wider North and Arctic region – mean it should remain central to the Royal Navy’s planning. Indeed, Chinese vessels have already been detected in the North Atlantic and PLAN submarines in the High North – it is a reasonable assumption they will be detected in the North Atlantic before long if they have not already.

The Royal Navy’s undersea capabilities

As shown in Table 1, the UK has access to an array of undersea capabilities, many of which are at the cutting edge of technological design.

Table 1: The Royal Navy’s undersea capabilities

CapabilityNowForecastUK ownedDistributeDetectDeterDefeatArea

1. Surveillance: The Integrated Undersea Surveillance System (IUSS) is an underwater sensor system of systems which aggregated and updated the array of ageing Cold War sensors originally called the Sound Surveillance System. It is US-owned and operated but has UK personnel embedded in its headquarters, and the Royal Navy headquarters in Northwood is granted access to information from it when required. The speed at which commercial options are being developed for underwater surveillance is noteworthy and an area that Britain should invest heavily in.

2. Aircraft: The P-8 Poseidon is the Royal Air Force’s (RAF) maritime patrol aircraft. All nine are now operational, but the number is deemed insufficient with the RAF requesting another three last year.

3. Frigates: Over the next 11 years or so, the Royal Navy will replace the eight towed array and five general-purpose Type 23 frigates with eight Type 26s and five Type 31s. Like P-8 Poseidons, frigates are important to the Royal Navy’s ability to wage anti-submarine warfare.

4. SSNs: SSNs are one of the Royal Navy’s most important capabilities: they provide the means to sink enemy submarines and surface combatants, and fire long-range cruise missiles to decimate inland targets. In addition, they can gather intelligence and integrate with amphibious Special Forces. The Royal Navy currently has six SSNs in commission: five Astute class (HMS Anson is at sea and conducting trials so not yet fully operational) and one ageing Trafalgar class (HMS Triumph). By 2027, the full complement of seven Astutes will be commissioned and the venerable HMS Triumph will retire. Although the number of Astute class vessels was increased from six to seven, their tasking will be taut. They will be required in the Wider North, North Atlantic, British home waters, Mediterranean and as part of Carrier Strike Group deployments – prioritisation will be as important as it will be difficult. Forward rotations to Western Australia will also begin ‘as early as 2027’ under the AUKUS agreement. A new SSN, ‘SSN-AUKUS’, will be developed jointly for the Royal Navy and Royal Australian Navy through the agreement, although it remains unclear how many vessels the Royal Navy will acquire.

5. Nuclear ballistic missile submarines (SSBNs): Currently, it can be said with confidence that the Royal Navy’s SSBN fleet is well equipped, now and for the future. The four Vanguard class vessels are being replaced by four Dreadnought class vessels, a transition which will maintain Britain’s ability to deter would-be aggressors or respond to their actions if necessary.

6. Autonomous underwater vessels (AUVs): The AUV industry is growing every bit as fast as the commercial surveillance systems at the top of this list. Here, the Royal Navy is taking a proactive stance and building stronger relationships with industry to exploit this capability as it matures.

7. Surveying: Britain’s survey capabilities are strong with HMS Scott (deep water), Protector (extreme latitudes) and RFA Proteus (recently taken up from trade for Ocean Surveillance) able to survey huge areas of ocean in their respective roles. There is also a lot of work going into developing uncrewed survey systems. Offsetting the strategic timeliness of purchasing Proteus (and Stirling Castle for mine countermeasure vessel support) is the decision to pay off HMS Echo and Enterprise early.

8. Mine countermeasures (MCM): This is an area where the Royal Navy is pursuing a technological solution at a commendable rate. But it will only be successful if paying off the existing capability is synchronised with the introduction of new cutting-edge technologies, thus maintaining the UK’s advantage.

Britain’s nuclear submarines: Distinguishing features

Although a comparison between the United States (US) Navy’s Virginia class and the Royal Navy’s Astute class quickly reveals two submarine classes which in terms of stealth, detection capabilities, and weaponry are world-leading, there are distinct advantages to the way Britain builds its vessels and trains those operating them. 

Certainly, the cost differential between the two is of note, with the latest Virginias costing just over US$4.3 billion (£3.4 billion) for the latest hulls compared to £2.4 billion for each Astute – a considerable saving. Money was saved on the Astute class’ design by using already proven parts of the (larger) Vanguard class reactors as well as parts of the (smaller) Trafalgar class such as diesel generators, power trains and other ancillary items. Although this technology was proven, making an oversized reactor fit a smaller boat and an under-powered diesel generator support a larger one caused problems in the early builds, but these have now been overcome. 

The Royal Navy also has an edge in the way it trains and qualifies its crews, in particular its commanding officers. The command qualifying course known as ‘The Perisher’ remains as stern a test of suitability for command as any course in the world. But perhaps the biggest difference is the US Navy’s insistence on qualifying its potential commanding officers as nuclear engineers along the way. The Royal Navy sees operators as operators and engineers as engineers – they have a different mindset and while they need to understand what each other is doing, they do not need to know it in detail. A commanding officer who has had an undiluted focus on leading and fighting a submarine throughout their career may prove a great advantage in wartime.


The need to distribute safely goods, energy and information on and below the high seas remains as important to the UK as ever. The requirement to deter, detect, and if necessary, defeat those that would wish to either disrupt this flow or harm the UK directly is only increasing. With this in mind, are the Royal Navy’s undersea capabilities sufficient for the global maritime century? Existing equipment is good, and ongoing efforts to find better and more efficient solutions to replace current stocks noteworthy. However, is there enough of any of it? No. 

Nonetheless, when looking ahead, there are some positives. The AUKUS agreement will equip the Royal Navy with the next generation of SSNs and reinvigorate Britain’s defence-industrial base with support from Australia and the US. The 2023 Defence Command Paper committed also to making the British Armed Forces more modern, agile and lethal, yet an extra £5 billion for the Ministry of Defence over two years, more money for service accommodation, and an aspiration to increase defence spending to 2.5% of Gross Domestic Product, may not be enough.

Indeed, it is evident Britain has enough equipment and expertise to operate effectively in the present undersea environment. But whether it has the depth to operate in the more volatile undersea domain of the future is an open question.

Tom Sharpe OBE is a partner at Special Project Partners, a communications consultancy. Previously, he spent 27 years in the Royal Navy, 20 of which were at sea.

This article is the fifth part of a special series for Britain’s World on underwater warfare. The series is kindly sponsored by Dr Carl Stephen Patrick Hunter OBE.

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