The future of underwater warfare

Technological change has been a constant theme in naval warfare and maritime strategy. Every new weapon or system prompts a response: the first revolution in underwater warfare, the use of submarines in 1914-1918, generated potent counter-measures, such as hydrophones, sonar and depth charges. The first Autonomous Underwater Vehicles (AUV) were the anti-submarine homing torpedoes of the Second World War, which were quickly followed by minesweeping platforms. The big question for the United Kingdom (UK) and other maritime powers is whether today’s new technologies could alter the operational/strategic balance between land and sea to their disadvantage. 

This is not a new issue. The RAND Corporation published a lengthy United States (US) Navy-funded study in 2009, offering sound, if cautious, conclusions. Since then, technology has moved quickly, but missions have not changed. This is critical: strategic context will shape the development and deployment of next-generation technologies at and under the sea. Major powers and alliances, which depend on sea communications for trade, resource flows, wartime cooperation and strategic effect ranging from economic sanctions to secure second-strike nuclear deterrence, are compelled to master these ‘challenger’ systems and devise effective counter-measures against them. This is why the Royal Navy bought its first submarines in 1901; it is also why it ordered, more recently, HMS/M Cetus.

In a major conflict, the underwater sphere matters insofar as it contributes to the battle for command of the surface of the sea, and the wider strategic picture beyond (e.g., submarines deploying land attack weapons). The deep ocean will not be the key to victory for Russia or the People’s Republic of China (PRC), terrestrial powers with limited, essentially negative interests at sea. Any naval threat they pose is, like so much of their propaganda, designed to distract attention from their vulnerabilities. Their strategic default settings are coastal defence, sea denial (which they share with Iran) and strategic deterrence. 

Strategic logic and long experience with previous examples of significant technological progress in the naval domain strongly indicate that the main beneficiaries of modern AUVs will be the dominant maritime powers, not land-based challengers. While continental powers seeking to undermine the existing order at sea may find the new systems attractive, they face significant problems in deploying them, not least geographies constrained by choke points. In war, the navies of terrestrial powers, too weak to secure and exploit sea control against maritime rivals, focus on sea-denial strategies. They attempt to limit the impact of maritime power on their vital interests, primarily by denying access to their coastal waters for power projection, while attacking the oceanic communications of maritime adversaries. While this last option can provide a potent distraction, the long history of such conflicts indicates that attacking commercial shipping and information is indecisive.

Attacking merchant shipping and sea-bed communications failed in both world wars because Britain and its allies maintained command of the surface of sea, deploying superior aero-naval forces to track down and destroy hostile submarines and fugitive surface ships, while imposing cumulative economic pressure. Above all, dominant seapowers deny continental rivals access to global resources, food, raw materials, industrial output, and personnel. In 1939-1945, Allied sea control isolated the Axis powers, which were defeated in sequence using sea-based power projection to secure strategic advantage on land and in the air. By 1944, Germany deployed submarines for the defence of Western and Northern Europe. At the tactical level, both sides deployed autonomous weapons and homing torpedoes, which proved to be particularly effective against submerged submarines. The Germans used similar weapons to sink small, cheap convoy escort vessels, a waste of resources when their key targets were merchant ships. 

The situation is largely unchanged today: the North Atlantic Treaty Organisation and associated nations have the naval power to command the sea. The protection of underwater pipelines and cables, for communications and commerce, will require more assets, and here AUVs act as force multipliers. They could also be effective as underwater sensor platforms operating under convoys, much as nuclear-propelled attack submarines (SSNs) currently operate under major naval formations.

For Britain and other maritime states, the most important response to AUV platforms and systems would be reinforcing sea control by upgrading and increasing current surface, sub-surface and air forces to maintain command of the surface. New AUV platforms will be significantly more useful when reinforcing and extending sea control, rather than attempting to defeat it. Early ideas for AUVs included submarine minesweepers and mobile sensor platforms; beyond this, tasking AUVs to defend undersea cables would be an obvious next step, not least by exploiting their long patrol duration. Clear rules of engagement – anything approaching the cables would be a target – would need to be set out. In truth, undersea cables are best secured by duplication and sea control – as they were in the world wars. Autonomous surface assets would be useful in such missions. 

At the other end of the strategic spectrum, deploying advanced AUVs capable of locating and sinking nuclear-powered, and especially nuclear-armed, submarines would transform the strategic balance, reducing or entirely vitiating current concepts of deterrence. 

The classic submarine mission – sinking merchant ships – would require large fleets of long-endurance UAVs and crewed craft to produce any strategic effect, and such a campaign would be highly unlikely in a major conflict given the myriad of more important tasks that such capabilities would be tasked with. Selected UAV sinkings might be used to distract assets from other tasks, but Russian, Chinese, or Iranian assets would find it difficult to access the major shipping lanes during a major conflict regardless. 

The critical attraction of AUV assets lies in their ability to supplement or replace costly, fragile, fallible and resource-hungry humans, who currently operate major underwater platforms. Recruiting and retaining highly qualified personnel for submarine service has never been easy. It will not be improved by ageing populations and demographic decline.

In theory, artificial intelligence (AI) could enable swarms of UAVs to challenge current naval operations, but there remain big problems to solve. Current platforms are slow, with low submerged endurance due to having to surface for diesel generators to recharge their batteries. Russia’s Poseidon submarine, nuclear-powered and nuclear-armed, is not configured for naval operations; it is a costly strategic system.

AI has the potential to enhance the effectiveness of AUVs by exploiting endless simulations of wargaming, military exercises and relevant combat experiences to train them. However, this open-ended ‘Perisher’ approach cuts both ways. Sophisticated UAVs would meet equally clever opponents. UAVs operated by nations in control of the surface of the sea would have the advantage of more secure data links that are better integrated into the battle space, with access to weapons and sensors on other platforms, as well as local direction. 

Battle space integration would address another potential issue. Replacing humans would tend to make AUV behaviour more predictable, eliminating the individual sense and feel that set the most successful submarine commanders apart from their equally well-trained peers. This degree of conformity would mirror the command practices of authoritarian or one-party states. It is worth noting that the largest warship ever sunk by a Russian or Soviet submarine was a stationary 1500-tonne destroyer. 

There is one overarching question to all this: how long can humans retain control of dynamic intelligent processes? This raises more moral and legal issues than military concerns. Who is responsible if an AUV commits a war crime, for example sinking a hospital ship, without a direct human order? How would the state deal with a rogue AUV, or one that had been captured by hostile powers? Britain might take the opportunity to shape the legal basis for deploying UAVs in combat. They will need failsafe systems.

It should be obvious that AUV assets will take on more missions and evolve into ever more effective combatants, operating alongside and potentially replacing crewed assets. Procuring AUVs in numbers may enable maritime powers to operate more offensively, particularly in strategic choke points, and as close-in blockade platforms. However, the critical mission for maritime powers will remain securing command of the surface of the sea, the essential enabler of sea control. Far from challenging maritime powers’ command of the sea, AI and AUVs should enhance their ability to maintain and exploit that command, as an alternative to costly commitments on land. 

Given the central role of sea control in the security of the UK and its global allies and partners, it is critical that the country take an integrated ‘seapower’ approach to the ocean and maritime security, linking technology, defence, shipping, trade, industry, communications and the law. Re-balancing national policy to maximise national maritime capability would be consistent with past practice, and Britain’s current ambitions. 

In conclusion: while the prospect of AUV submarines powered by AI roaming the deep ocean, striking submarine cables, ships and land targets at will may add a frisson of uncertainty to current anxieties, the technology is costly and offers limited return for continental powers focused on sea denial and area defence. It is more likely that, in the short term, AUVs develop into effective components of mixed underwater and three-dimensional security and combat forces which will enhance sea control, rather than challenge it. AUVs operating as fugitives in a hostile ocean will find it difficult to achieve tactical, let alone strategic effect.

Prof. Andrew Lambert is Laughton Professor of Naval History at the Department of War Studies at King’s College, London. He is also a Member of the Advisory Council of the Council on Geostrategy.

Embedded image credit: NOAA Photo Library (CC BY 2.0 cropped and overlaid)