Global Deep Dive - Undersea Cable Sabotage Underscores Ongoing Threat of Grey Zone Warfare
Key Takeaways:
The targeting of undersea cable infrastructure highlights the growing use of grey zone warfare by Western adversaries such as China and Russia.
Nations targeted by grey zone tactics are best positioned to mitigate the threat through collaboration. In the case of protecting deep-sea cables, solutions include enhanced surveillance, AI integration, and deploying UUVs.
The multitude of challenges posed by grey zone warfare demands ongoing multilateral cooperation and investment. This will be made harder by actors who continue to refine new methods and technologies to undermine and neutralise countermeasures.
Undersea Cables in Grey Zone Warfare
Grey Zone warfare refers to activities that “occur between peace and war”, including nefarious economic actions, cyberattacks, assassinations, and disinformation campaigns. They can be used by state and non-state actors, providing a means to destabilise an adversary without risking open warfare. Although grey zone activities are nothing new, technological developments have widened their scope and impact. In the modern world, where great powers are constrained from direct conventional warfare with one another by the threat of nuclear escalation, such methods have provided nations with an alternative means to pursue strategic objectives.
One particularly interesting method of grey zone warfare to emerge is the sabotaging of undersea cable infrastructure. Undersea cables are the fibre-optic lines found along the ocean floor that form the backbone of the global internet. Capable of transmitting multiple terabits of data per second, they offer the fastest and most reliable method of data transfer available today. With up to 99% of intercontinental data transmission taking place through submarine cable systems, taking the infrastructure offline causes significant economic losses, service disruptions, and threatens national security. Governments are at particular risk, along with telecommunications companies, financial institutions, tech giants, and other businesses reliant on global data transfer.
China
In recent years, the US and its allies have increasingly fallen victim to grey zone warfare strategies. China has emerged as a prominent employer of such underhanded tactics. Beijing’s actions in the South China Sea, such as the construction and militarisation of new islands, and the harassment of rival claimants through ship-ramming, water cannons, and high-powered lasers, are cogent examples. Taiwan has been a frequent target of Beijing’s grey zone tactics. For instance, as a result of Chinese military aircraft regularly crossing the Air Defence Identification Zone, Taipei has to scramble fighter jets on an almost daily basis. Other Chinese tactics include rehearsing the implementation of a blockade, attempting to steer public discourse toward their political agenda, and frequent cyberattacks.
Concerns have also grown regarding China’s targeting of critical undersea cable infrastructure. On 12 June 2025, a Taiwanese court handed a three-year prison term to a Chinese captain named Wang for cutting an undersea cable connecting Taiwan and the Penghu Islands. The incident occurred after Wang's Togolese-registered ship, Hong Tai 58, anchored in a restricted no-anchoring zone on 22 February 2025 and drifted over the cable, causing it to snap. With cross-strait tensions rising, many suspect Beijing to be responsible. This was not an isolated incident. Just one month earlier, on the morning of January 03 2025, the Trans-Pacific Express (TPE) cable, connecting Taiwan to the US, Japan, South Korea, and China, was also damaged. On that occasion, Taiwanese authorities alleged that a Cameroon-registered, Hong Kong-owned freighter named the Shunxing-39 was responsible.
The incidents likely provide a window into how Beijing could isolate the island during an invasion or blockade, with the cables likely to be among China’s first targets in such an event. With Taiwan connected to the outside world through 15 undersea cables, severing them could impact military communications, disrupt financial markets, compromise emergency services, and spread panic among the population. This would cause significant challenges for Taipei, which would be attempting to organise the defence of the island.
Sino-Russian Collaboration
One of the particularly alarming things about the threat posed by grey zone warfare is that Beijing appears to not be acting alone. A recent report published by the China Strategic Risks Institute analysed 12 instances in which national authorities had investigated alleged undersea cable sabotage between January 2021 and April 2025. Of the ten cases in which a suspect vessel was identified, eight were linked to China or Russia through flag-state registration or company ownership. The involvement of Chinese vessels in breakages in Europe and Russian vessels near Taiwan implies coordination between Beijing and Moscow.
In the cases of China and Russia, undersea cable sabotage is often facilitated by shadow fleets, referring to ships that operate covertly or with concealed ownership that are suspected of conducting hostile or clandestine activities. States can deploy these fleets to carry out operations that affect adversaries while preserving deniability. For example, China dismissed the recent cable incident by labelling such cases as “common maritime accidents”. The phenomenon attracted a significant amount of media attention after the outbreak of the war in Ukraine, when Russia used such vessels to evade Western sanctions. Several sources place the size of China’s fleet at between 300 and 600 vessels, while Russia’s shadow fleet is frequently reported to number around 600.
Solutions
With the term grey zone warfare describing a range of methods, addressing the threat demands a similarly extensive range of solutions. Using sabotaged undersea cable infrastructure as an example, there is evidence of strategies being developed to mitigate the threat. After the attack on the Nord Stream pipelines in September 2022 highlighted the vulnerability of undersea infrastructure, then UK Defence Secretary Ben Wallace accelerated the procurement of a new multi-role ocean surveillance capability ship to safeguard critical national infrastructure. In January 2025, reports also revealed that the UK and several allies would soon be employing an AI-assisted computer programme to monitor large areas of the sea and track vessels by drawing on a variety of data. The move was directly aimed at tracking the movement of Russia’s shadow fleet. In the same month, NATO initiated Operation Baltic Sentry to bolster its maritime presence and surveillance in the Baltic Sea through the deployment of aircraft, ships, and naval drones. However, as allocating so many assets is resource-intensive, interest has been growing around the use of uncrewed underwater vessels (or UUVs) to patrol high-risk sections of undersea cable routes. Even something simpler, such as burying the cables deeper in high-risk locations, could make a positive difference.
With growing political will, multiple countries are recognising and developing solutions to the challenges posed by grey zone warfare. However, the matter will require ongoing multilateral cooperation and investment. This will be made harder by actors who continue to refine new methods and technologies to undermine and neutralise countermeasures. In March 2025, the China Ship Scientific Research Centre unveiled a new ship capable of cutting cable lines at depths of up to 4,000 metres under the guise of supporting “marine resource development”.