21 March 2025
Over the last three decades, uncrewed vehicles have transformed modern warfare by enhancing operational efficiency, reducing risks to human operators, and enabling real-time detection, decision-making, and target engagement. Dramatic footage from the Russo-Ukrainian War has piqued the public’s attention in unmanned technology, whether it is aerial drones conducting precision strikes on everything from large energy plants to individual infantrymen, or Ukraine’s uncrewed boats wreaking havoc on Russia’s Black Sea Fleet.
The impact of uncrewed vehicles on warfare extends beyond these domains. In recent years, there has been rapid progress in technologies related to uncrewed underwater vehicles (UUVs). Their proliferation among both state and non-state actors is introducing new threats and altering the operational environment in the oceans.
UUVs are not new or revolutionary innovations. Scientific communities, offshore oil and gas industries, and companies involved in undersea communication and power cable operations have long utilized them. Similarly, navies have employed UUVs since the 1960s.[1] The U.S. Navy pioneered the use of Remotely Operated Vehicles (ROVs) for recovering objects from the seafloor and conducting deep-sea surveys and mapping. These early models were tethered to a mothership by cables and thus had limited range and flexibility. The obvious solution was to eliminate the cable, but this introduced challenges in underwater communications.
Radiofrequency (RF) waves become useless underwater due to saltwater conductivity. Acoustic communication, which transmits soundwaves to carry commands and data, is more viable but has issues such as interference from ambient noise, unpredictable signal travel through ocean layers, and significant delays over long distances due to the slow speed of sound in water. This hampers real-time command and the steering of UUVs over long distances. Other methods, such as blue-green lasers and quantum communications, are under development but remain far from operational deployment.
Instead, technology shifted toward increasing UUVs’ autonomy by removing man-in-the-loop operators. This transition has been facilitated over the past decade by advances in digital technologies, including microelectronics, enhanced processing power, and machine learning. Improvements in batteries and propulsion, miniaturised sensors, materials, and navigation systems have further benefitted the development of autonomous underwater vehicles (AUVs). The AUVs have become so commonplace that the term UUV has become almost synonymous with AUV.
Traditionally, militaries spearheaded underwater technology development, but in recent years, the demand from oil and gas industries and undersea cable operators has driven technological innovation. Navies and public procurement authorities now often leverage technologies developed for commercial use, and several navies are adopting commercial-off-the-shelf (COTS) UUV solutions.[2]
The missions fulfilled by UUVs can be broadly divided into three categories:
Traditional Naval Tasks
When dealing with undersea warfare, major naval powers have traditionally focused on antisubmarine warfare (ASW), intelligence-surveillance-reconnaissance (ISR), and mine warfare. UUVs have been pressed into duty to assist these traditional tasks. For example, the U.S. Navy, which has a long history of using specialized submarines, has integrated UUVs with manned submarines for tasks such as mapping key areas of the sea floor frequented by adversary submarines and recovery of material from seabed. To achieve this, four of the U.S. Navy’s Ohio-class nuclear-powered ballistic missile submarines were converted into multi-mission platforms capable of carrying UUVs of different types and sizes. The details and exact roles of these UUVs are murky, but the seizure of several American underwater spy drones over the last 20 years, provide proof of their widespread use for intelligence-gathering and other classified tasks.[3] Similarly, Russia is known to operate UUVs in conjunction with its fleet of three nuclear-powered ballistic missile submarines converted into massive motherships to carry out comparable ISR and secret missions.[4] UUVs are also deployed from Russia’s very large fleet of “scientific research” surface ships.[5]
China has also adopted UUVs, as it tries to expand its naval power. Its arsenal includes extra-large UUVs as well as small, dual-use UUVs that do marine and hydrographic surveys. Like other navies, the Chinese also use commercial UUVs.[6] Several glider-type AUVs seized by Pacific nations reveal the capabilities of these lower-end Chinese UUVs. two-meter-long vehicles with a torpedo-shaped body fitted with antennae and sensors. Devoid of propulsion system, they use an internal system to alter buoyancy, repeatedly diving then surfacing to move forward. They can operate for up to 30 days and dive down to four miles. The U.S. also deploys these glider-type AUVs for hydrographic survey and for detailing the contours of the seabed with ASW utility.[7]
A growing concern is the potential use of AUVs to detect and continuously trail ballistic missile-carrying submarines (SSBNs). Such heightened surveillance could erode the ability of SSBNs to remain undetected, th4reatening their survivability. SSBNs are the most critical second-strike assets for leading nuclear-weapon states. If adversaries can successfully track and target these submarines, it would risk compromising the credibility of a nuclear-armed state’s second-strike capability, retaliatory capability, which is fundamental to the doctrine of Mutually Assured Destruction (MAD) and strategic stability.[8] UUVs are also used in mine hunting and are being used not only to detect mines but as moveable mines themselves, lying quietly on the ocean floor until activated.[9]
One-Way Attack (OWA)
In recent years, UUVs have been fitted with explosives to function as low-end torpedoes. Iran may be at the forefront of this OWA trend blending UUV technology with torpedoes. The outcome is a long-endurance, slow-running UUV that quietly approaches its target and explodes below the waterline for maximum damage. These Iranian weaponized UUVs are fitted with very little or no targeting capability and are therefore suited for sneak attacks on ships at anchor or pier-side as well as for attacks on stationary targets such as oil rigs or other critical infrastructure targets. Some observers have said that these weapons are the underwater equivalents of Iranian Shaheed aerial drones, but unlike the Shaheed drones, they use surprise and stealth rather than overwhelming numbers.[10] Attacks on merchant ships at anchor in the Persian Gulf between 2019-2020 gave rise to speculation that low-tech Iranian OWA-UUVs may have been used along with limpet mines.[11][12]
A worrying development has been Iran supplying OWA-UUVs and/or associated know-how to its proxies. In 2021, the Israeli Navy intercepted a small, GPS-guided AUV carrying 30 kilograms of explosives launched by Hamas from Gaza, possibly aimed at the nearby Tamar offshore gas rig.[13] During the October 7th raids on Israel two years later, Hamas attempted to launch another makeshift semi-submersible assembled from compressed gas cylinders coupled to a combustion engine, snorkel, and propeller borrowed from a commercial diver propulsion vehicle (DPV). Besides explosives and a rudimentary impact fuse, the device carried a GoPro style camera for guidance by a remote operator.[14] It was quickly detected and neutralized by the Israeli Navy. While rudimentary, the second Hamas device illustrates the ease with which non-state actors can get their hands on the parts to assemble sneak underwater OVA-UUVs. Other events in the Middle East also suggest that Iran could be sharing their technology. In 2024 the U.S. Navy reported striking two such vehicles while still on shore in Yemen.[15] A few months later, the Houthis acknowledged their possession of OWA-AUVs.[16] In Lebanon, Hezbollah may also have AUVs.[17]
Several other states, including Ukraine, South Korea, China, and Taiwan, are pursuing OWA-AUVs. Russia has also invested in the technology, whose KANYON (aka Poseidon) nuclear-propelled, nuclear-armed intercontinental torpedo[18] is, in effect, a giant OWA-AUV. Moscow justified the KANYON by saying it is an asymmetric response to the U.S. ballistic missile defence shield, which is not categorically different from other navies’ motivations.
Russia was quickly mimicked by North Korea, who have invested in large, professional OWA-AUVs. One of their devices is a truck-sized, torpedo-shaped vehicle fitted with active-passive sensors for terminal homing that is reportedly capable of carrying a nuclear warhead besides conventional explosives.[19] The device uses a diesel engine, so it must float on or very near the surface of the sea to breath oxygen, but it has a reported range of 1,000 kilometres. Together, Russia and North Korea have carried UUVs into the realm of nuclear deterrence.
“Made in China” AUVs may soon begin to flood international arms markets. Several other states – among them Ukraine, South Korea, and Taiwan – are actively pursuing OWA-AUVs. One commentator compared the recent interest in UUVs to the rush for diesel-electric submarines and missile boats five decades ago. Accordingly, armed UUVs are seen as the next asymmetrical must-have items for smaller navies, because they promise a way to stand-up to the much more powerful conventional navies. Unlike crewed subs they are low-cost, quick to build, quick to get operational, and have minimal training overhead.[20]
Critical Infrastructure
The 2022 Nord Stream pipeline explosions underscored the vulnerability of undersea critical infrastructure. Close to 500 underwater fibreoptic cables carry 97 percent of the world’s internet traffic.[21] An ever-growing number of offshore windfarms rely on submarine cables for passing on their power to shore. Such grids may not be vulnerable to a single point of failure, but they would buckle under a coordinated attack.[22] Likewise, underwater pipelines, offshore oil and gas rigs, subsea railway and road tunnels, columns and towers of oversea bridges, oil and gas terminals, ports, naval bases, and dockyards are all susceptible to underwater sabotage.
The act of sabotage on the Nord Stream was not an isolated incident. Recently, several undersea communication and power cables in the Baltic Sea and off the coast of Taiwan were severed under suspicious circumstances by merchant ships dropping and dragging their anchors.[23] [24] Additionally, there were at least two public domain incidents — both targeting Norway — in which fibreoptic cables were severed at great depths, ruling out ship anchors or trawling nets as possible culprits.[25] American and Soviet submarines inflicted damage on cables during the Cold War years, so there is historical precedent, however, the threat of UUVs is new and worrying as their stealth makes them difficult to track. If countries are not able to attribute blame for an attack, punishment and deterrence become more difficult.
On the other hand, UUVs could also become a solution for mitigating risks. The oceans are too vast and navies too small to constantly patrol and protect widely distributed underwater infrastructure. Comparatively low-cost and expendable AUVs in large quantities can survey undersea cables, pipelines, and other undersea installations. Some navies have looked to offshore oil and gas industries for inspiration and are contemplating uncrewed outposts placed on the ocean floor, where UUVs can upload data and download orders while recharging their batteries.[26]
In fact, private sector entities working offshore have accumulated more advanced hardware, technology and operational experience than their navy counterparts. As of 2024, all European navies fielded a total of 20 UUVs among them,[27] whereas within days of the Nord Stream incident offshore companies were able to field 600 advanced UUVs to scan every centimetre of pipelines, power and data cables around Europe. This is a stark reminder of how technology and capabilities that once seeped from the military into the civilian world is now moving in the other direction.[28]
Conclusion
The rapid proliferation of a new generation of UUVs is reshaping the operational environment at sea. Naval and merchant vessels as well as offshore and coastal facilities face new challenges from hard-to-detect UUVs behaving like low-tech, low-speed, but long-endurance loitering torpedoes. At the same time, these vehicles offer opportunities for enhanced surveillance and protection. The future of naval warfare will likely include seabed sensor networks and UUVs working in tandem to conduct surveillance, trailing, and strike missions.
[1] Marine Technology Society ROV Committee, “History,” https://rov.org/history/?utm_source=chatgpt.com
[2] Elisabeth Gosselin-Malo, “How AUVs are helping safeguard Europe’s underwater infrastructure,” C4ISRNET, 17 April 2023, https://www.c4isrnet.com/unmanned/2023/04/17/how-auvs-are-helping-safeguard-europes-underwater-infrastructure/?utm_campaign=dfn-ebb&utm_medium=email&utm_source=sailthru&SToverlay=2002c2d9-c344-4bbb-8610-e5794efcfa7d
[3] Joseph Trevithick, “Ohio Class Guided Missile Submarine Deployed Underwater Drones On Award Winning Secret Missions,” The War Zone, 9 January 2025, https://www.twz.com/sea/ohio-guided-missile-submarine-deployed-underwater-drones-on-award-winning-secret-missions?utm_term=The%20War%20Zone_Wire_01.10.25&utm_campaign=The%20War%20Zone_Dedicated/Sales&utm_source=Sailthru&utm_medium=email
[4] Tyler Rogoway, “Russia’s Massive Arctic ‘Research’ Submarine Will Be The World’s Longest,” The War Zone, 3 May 2017, https://www.twz.com/9928/russias-massive-arctic-research-submarine-will-be-the-worlds-longest
[5] Nurlan Aliyev, “The Mayhem of Russia’s ‘Research’ Fleet,” War on The Rocks, 7 January 2025, https://warontherocks.com/2025/01/the-mayhem-of-russias-research-fleet/?utm_campaign=dfn-ebb&utm_medium=email&utm_source=sailthru
[6] H.I. Sutton, “China’s New Extra-Large Submarine Drones Revealed,” Naval News, 16 September 2022, https://www.navalnews.com/naval-news/2022/09/chinas-secret-extra-large-submarine-drone-program-revealed/
[7] Joseph Trevithick, “Chinese Underwater Sea Glider Drone Caught ByFisherman In The Philippines,” The War Zone, 2 January 2025; https://www.twz.com/sea/chinese-underwater-sea-glider-drone-caught-by-fisherman-in-the-philippines?utm_term=The%20War%20Zone_Wire_01.03.25&utm_campaign=The%20War%20Zone_Dedicated/Sales&utm_source=Sailthru&utm_medium=email
[8] Bryan Clark, “Undersea cables and the future of submarine competition,” Bulletin of the Atomic Scientists, 15 June 2016, https://www.tandfonline.com/doi/full/10.1080/00963402.2016.1195636
[9] Defense News, “Europeans wade into fighting seabed threats with drones and sensors,” 9 January 2023, https://www.defensenews.com/global/europe/2023/01/09/europeans-wade-into-fighting-seabed-threats-with-drones-and-sensors/?utm_source=sailthru&utm_medium=email&utm_campaign=dfn-enr
[10] H.I. Sutton, “World Survey of Underwater Attack Drones (OWA-AUVs),” hisutton.com, 3 January 2024, http://www.hisutton.com/Guide-To-Underwater-Attack-Drones.html
[11] Samuel Chamberlain, “First assessments blames Iran for Middle East ship explosions, official says,” Fox News, 13 May 2019, https://www.foxnews.com/world/iran-middle-east-ship-explosions-assessment
[12] H.I. Sutton, “New Iranian Weaponized Underwater Drone,” hisutton.com, 16 March 2022, http://www.hisutton.com/Iran-IRGC-Weaponized-UUV.html
[13] Judah Ari Gross, “IDF says it thwarted underwater drone attack by Hamas from northern Gaza,” Times of Israel, 18 May 2021, https://www.timesofisrael.com/idf-says-it-thwarted-underwater-drone-attack-by-hamas-from-northern-gaza/
[14] H. I. Sutton, “First Details Of Hamas’ New Submarine Drone Weapons,” Naval News, 1 November 2023, https://www.navalnews.com/naval-news/2023/11/first-details-of-hamas-new-submarine-drone-weapon/
[15] Jonathan Lehrfeld, et.al., “All the Houthi-US Navy incidents in the Middle East (that we know of),” Military Times, 12 February 2024 (updated 24 October 2024), https://www.militarytimes.com/news/your-military/2024/02/12/all-the-houthi-us-navy-incidents-in-the-middle-east-that-we-know-of/?utm_campaign=dfn-ebb&utm_medium=email&utm_source=sailthru
[16] Mina Adel, “Dealing with the Houthis,” English Ahram, 5 November 2024, https://english.ahram.org.eg/News/534781.aspx
[17] H. I. Sutton, “First Details Of Hamas’ New Submarine Drone Weapons,” Naval News, 1 November 2023, https://www.navalnews.com/naval-news/2023/11/first-details-of-hamas-new-submarine-drone-weapon/
[18] Silky Kaur, “One nuclear-armed Poseidon could decimate a coastal city. Russia wants 30 of them.” Bulletin of the Atomic Scientists, 14 June 2023, https://thebulletin.org/2023/06/one-nuclear-armed-poseidon-torpedo-could-decimate-a-coastal-city-russia-wants-30-of-them/
[19] H. I. Sutton, “North Korea’s New Torpedo Drone,” hisutton.com, 20 July 2023, http://www.hisutton.com/North-Korea-Nuclear-Torpedo-Drone.html
[20] H.I. Sutton, “China Reveals Another New Armed XLUUV: UUV-300,” hisutton.com, 9 May 2024, http://www.hisutton.com/China-UUV-300.html
[21] Jack Detsch and Keith Johnson, “NATO Wants to Boost Its Undersea Defenses,” Foreign Policy, 24 June 2024,
[22] Morten Soendergaard Larsen, “Russian ‘Ghost Ships’ Are Turning the Seabed Into a Future Battlefield,” Foreign Policy, 2 May 2023, https://foreignpolicy.com/2023/05/02/russia-europe-denmark-spy-surveillance-ships-seabed-cables/
[23] Linus Höller, “The shallow Baltic Sea holds deep secrets about a hybrid war on NATO,” Defense News, 9 December 2024, https://www.defensenews.com/special-reports/2024/12/09/the-shallow-baltic-sea-holds-deep-secrets-about-a-hybrid-war-on-nato/?utm_source=sailthru&utm_medium=email&utm_campaign=dfn-enr
[24] Thomas Newdick, “Taiwan Coast Guard Blames Chinese-Owned Ship For Cutting Undersea Communications Cable,” The War Zone, 16 January 2025, https://www.twz.com/news-features/taiwan-coast-guard-blames-chinese-owned-ship-for-cutting-undersea-communications-cable?utm_term=The%20War%20Zone_Wire_01.07.25&utm_campaign=The%20War%20Zone_Dedicated/Sales&utm_source=Sailthru&utm_medium=email
[25] Thomas Newdick, “Undersea Cable Connecting Norway With Arctic Satellite Has Been Mysteriously Severed,” The War Zone, 11 January 2022, https://www.twz.com/43828/undersea-cable-connecting-norway-with-arctic-satellite-station-has-been-mysteriously-severed
[26] Bryan Clark, “Undersea cables and the future of submarine competition,” Bulletin of the Atomic Scientists, 15 June 2016, https://www.tandfonline.com/doi/full/10.1080/00963402.2016.1195636
[27] Nick Childs speaking at “Critical Infrastructure: The Maritime Challenge,” IISS Events, 20 March 2024, https://www.iiss.org/events/2024/02/critical-infrastructure-the-maritime-challenge/
[28] The Economist, “How oceans became new technological battlefields,” 2 July 2023, https://www.economist.com/special-report/2023/07/03/how-oceans-became-new-technological-battlefields
