RFA Proteus begins operations as seabed warfare threats increase

A recent article in the Sunday Times revealed more details about Russian undersea activities directed against UK interests. Here we look in more detail at the specific threats and how RFA Proteus and the Royal Navy are gradually improving seabed warfare (SBW) capabilities.

Subsea espionage intensifies

The RN has discovered Russian surveillance devices hidden in UK waters. These sensors, some of which were recovered after washing ashore while others were detected by RN vessels, are suspected of being part of an intelligence-gathering effort targeting the Vanguard class SSBNs. The location of these discoveries has not been publicised but the boats transiting in and out of the Firth of Clyde are most vulnerable to detection in this area. The RN has now switched to autonomous or minimally crewed boats to conduct regular route surveys. By deploying side scan sonars to frequently map the seabed in high resolution, any objects not recorded in previous surveys are obvious and can be promptly investigated.

This is form of spying not entirely new as it is believed the Soviet Navy routinely deployed submarines for intelligence-gathering operations and attempted to lay underwater acoustic sensors near NATO naval facilities, cables and strategic maritime chokepoints. NATO forces performed similar missions. As an example, In 1971 the US Navy and CIA began operation Ivy Bells, laying a recording device on a communications cable linking Russian naval bases in the Sea of Okhotsk.

Uncrewed Underwater Vehicle technology has made such intrusions far easier. Since 2020, Russian UUVs have been detected in proximity to deep-sea communication cables in the North Atlantic and adjacent seas. These UUVs are remotely operated and were deployed from long range. It is clear they were attempting to interfere with, or gain intelligence from, subsea data infrastructure although so far, there is no public evidence that any attempt to compromise UK cables has succeeded. Less well-publicised is the existence of military sub-sea cables vital to NATO operations around the world. This includes cables linking seabed ASW sensor arrays to data processing centres ashore which are prime targets for Russian interference.

While media attention has often focused on the Russian intelligence-gathering surface vessels such as the Yantar, which are known to operate close to NATO cables and seabed infrastructure, this is only part of a much broader threat. Although the voyage of Yantar prompted a more assertive response when she detoured over cables in the Irish Sea in November 2024, the greater concern is the deeper waters beyond the continental shelf. It is much easier to police waters close to home than detect and deter activity in the deep ocean where Russia can covertly deploy specialised nuclear-powered submarines, mother ships to small submersibles.

There is also a strong suspicion that superyachts owned by Russian oligarchs have been used as platforms for undersea reconnaissance. Several are equipped with moon pools in the centre of the hull that allow the discreet launch and recovery of submersibles, potentially offering another covert method to conduct surveillance or deliver seabed sensors.

Tentative SBW steps

Proteus, the UK’s first Multi-Role Ocean Surveillance Ship (MROS) was purchased in January 2023. Despite the ‘rapid procurement’, getting her into service has taken more than two years but she is now operational. Once into her stride, it is planned she will be deployed for up to 330 days a year. The RFA crew rotate every 4 months or so but a shortage of qualified personnel could limit this. Under Navy Command direction, the RFA has to decide which of the 5 or 6 vessels that it can find crews for will remain active. Currently, it appears Proteus is being prioritised over the Bay-class vessels.

Early operations are developmental trials are already underway including closing with the Russian seabed spy ship Yantar in the Irish Sea last year. She also conducted operations off Norway (where she was originally built) in February and docked in Bodø hosting the Defence Secretary, John Healy and his Norwegian counterpart. Proteus was operating again in the Irish Sea in March and embarked RN specialists for the first time. These personnel came from X-Ray Squadron of the Mine-Hunting and Threat Exploitation Group (MTXG) and members of the Diving Threat Exploitation Group (DTXG).

The MoD stated that Proteus would “participate in exercises in the Baltic Sea” following the visit to Norway, possibly joining the NATO Baltic Sentry policing mission estabished in January. However, the trip to the Baltic has not yet materialised and at the time of writing, she has returned to the North Sea and is alongside at Kirkwall Harbour in the Orkneys.

RFA Proteus carries several advanced underwater vehicles as part of its threat detection and mitigation capability. The newest of the toys is the AEUK SeaCat, a 3-metre-long UUV with a high-resolution side scan sonar array. AEUK were awarded a £32m contract in 2022 for this system that was initially focused on mine countermeasures but can also be deployed in seabed warfare operations. SeaCat can operate at depths of up to 300 meters for up to 24 hours. It is up to 6 times more efficient at locating underwater objects than traditional shipboard mine-hunting sonars.

Complementing the SeaCat is the larger Gavia UUV, capable of diving to 1,000 metres, able to reach the deepest parts of the majority of the UK’s surrounding waters. For more complex tasks such the collection of evidence, recovery of equipment or underwater repairs, Proteus can also deploy the Defender, a remotely operated vehicle (ROV) that can be equipped with robotic arms and tools. DSTL Porton Down recently developed new manipulator arms for this system, capable of delivering and placing shaped charges to neutralise underwater threats, and this was tested in recent exercises off Norway.

Proteus has a large moon pool in the centre of the aft deck, this allows UUVs or ROVs to be lowered to the seabed directly below the ship and offers sheltered conditions protected from wind, waves and spray, reducing motion impact during delicate operations. The moon pool is normally covered by a heavy deck hatch but when the pool is in use, the hatch is lifted by the 120-tonne crane into a dedicated storage crib on the port side

For work in very deep water, up to 4,000m the MoD Salvage & Marine Operations (SALMO) team has acquired the FET Perry XLX-C heavy-duty ROV with manipulator arms for working on seabed objects. This kind of work requires specialist operators and a dedicated launch and recovery system. To accommodate heavier vehicles such as this, Proteus has been fitted with a luffing A-frame on her starboard side – the frame can be tilted, or ‘luffed’, to deploy the ROV over the side.

Stepping up

Discussions are now ongoing about acquiring a second vessel to complement Proteus. MROS(2) had originally been planned as a bespoke design built in the UK, to serve jointly as a replacement for the ocean survey vessel HMS Scott with additional seabed warfare capabilities. However, the urgency and scale of the risk to UK infrastructure suggests purchasing another second-hand vessel (or vessels) would still be a quicker way to address the problem, despite the ponderous entry into service of Proteus.

The renewed threat to subsea infrastructure has prompted some in the RN to question whether the UK should restore its mine-laying capability, something it has not possessed since the Cold War. The last British sea mines were dismantled in 1992 due to ethical concerns and the perception they were obsolete. However, the strategic context has changed.

In March 2025, Denmark announced the procurement of several hundred naval mines for delivery between 2027-29. Their aim is to bolster its defence of internal waters and support NATO’s collective deterrence posture. Australia also recently committed $500 million to acquire modern naval mines to defend its coasts from potential Chinese incursions. Several Baltic states, including Poland, have also signalled their intention to exit international treaties banning anti-personnel and anti-ship mines. Although no official proposal has been tabled within the current UK SDR, discussions within the RN suggest that defensive minefields could play a role in protecting key maritime approaches and infrastructure from enemy submarines and uncrewed intrusions.

There have been at least 11 instances of damage to subsea infrastructure in the Baltic Sea, the discovery of covert sensors laid on the seabed close to the UK and Russian UUVs found near undersea cables. These are just recent incidents in the public domain but the full scale of this activity is likely much greater than has been revealed so far. This demonstrates that the potential threat that has been talked about for some years is materialised into something very real.

There is a clear need to further expand the RN’s seabed warfare capabilities. The technology and platforms already exist, and in many ways, it is easier to scale up SBW capabilities rapidly than to increase ASW strength or respond to other more high-end threats. The obstacles for the RN are generally prosaic: obtaining the funding, developing the CONOPS for this new battlespace and ensuring there is enough SQEP to crew commercially-derived platforms with niche skills such as marine engineers, dynamic positioning-qualified officers and ROV operators.