UK Reveals SG-1 Fathom Drone as an Undersea Shield Against Russian Submarine Activity.

The UK Ministry of Defence has launched Atlantic Bastion, a new hybrid undersea surveillance network anchored by Helsing’s SG 1 Fathom autonomous gliders. The system aims to counter increased Russian submarine activity by giving the Royal Navy a persistent, scalable way to track threats across the North Atlantic.

On December 8, 2025, the UK Government formally rolled out its Atlantic Bastion programme, a next-generation undersea awareness network that UK officials describe as a major step in rebuilding Cold War-era coverage across the North Atlantic. At its core is Helsing’s SG 1 Fathom, a compact autonomous glider that Defence Secretary John Healey says will work alongside frigates, attack submarines, and RAF P-8A aircraft to protect seabed infrastructure and key maritime corridors. Early Ministry of Defence material frames the project as a strategic answer to a more active Russian undersea presence around British waters.
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The SG-1 fathom is a compact autonomous underwater glider that uses advanced acoustic sensors and AI to silently track low-signature submarines and protect UK seabed infrastructure (Picture source: Helsing).

SG-1 Fathom is a subsurface glider just 1.95 metres long and 28 centimetres in diameter, weighing around 60 kilograms, small enough for two sailors to handle on a quay or the deck of a workboat. Instead of using a noisy propeller, the vehicle adjusts its buoyancy and wings to translate vertical motion into a slow, efficient forward glide at roughly 1 to 2 knots. Helsing specifies an endurance of up to three months, with the glider able to cruise through the water column or sit quietly on the seabed as a listening node.

SG-1 is best understood as a sensor truck for Lura, Helsing’s underwater AI suite. The glider carries acoustic sensors and onboard processing that run a large acoustic model trained on decades of naval sonar data. Company material and specialist reporting indicate Lura can classify and localise very faint signatures, reportedly down to targets an order of magnitude quieter than previous AI systems and at speeds several dozen times faster than a human sonar team. In practical terms, that means an SG-1 swarm can sift huge acoustic data sets in real time at the edge, only sending back high-value detections instead of raw recordings.

Under Atlantic Bastion, the Royal Navy intends to weave those gliders into a wider underwater constellation stretching from the approaches to the English Channel through the GIUK gap and up toward the Norwegian Sea. MoD material describes a digital targeting web that will fuse SG-1 and Lura outputs with shipborne sonars, RAF P-8A Poseidon patrol aircraft, and submarine sensors, all connected through AI-powered acoustic detection and command networks. In that architecture, SG-1 does not replace frigates or attack submarines; it cues them, turning scarce high-end platforms into finishers while the gliders provide the wide-area search and persistent track keeping.

For day-to-day operations, the drone’s small footprint is a major advantage. Helsing stresses that SG-1 can be launched from commercial vessels, auxiliaries, or small naval craft, supporting rapid dispersal across choke points or around critical energy and data links. A single operator ashore or afloat can manage hundreds of gliders, planning missions, monitoring health, and receiving alerts. When a glider detects an interesting contact, it can surface briefly to transmit via satellite or other RF links, then dive again, limiting its exposure to adversary electronic surveillance while still feeding the Bastion network.

Strategically, the UK is explicit about the main problem set: Atlantic Bastion responds to rising Russian underwater activity around British waters, including intelligence collection by vessels such as the spy ship Yantar, and concerns about covert interference with seabed infrastructure. A dense lattice of SG-1 Fathoms around cables, offshore wind farms, and gas pipelines gives London a way to detect suspicious traffic early and build a pattern of life around Russian submarines and auxiliary vessels, complicating any attempt at deniable sabotage. For NATO, similar constellations could eventually cover the wider North Atlantic and Norwegian Sea, modernising the Cold War era SOSUS mindset with mobile, AI-enabled nodes.

The industrial story behind SG-1 is just as important. Helsing is standing up a Resilience Factory in Plymouth to mass produce the gliders for the UK and allies, offering sovereign, distributed manufacturing and easier spiral upgrades. The platform itself has its roots in environmental gliders developed by Blue Ocean, now militarised through partnerships with Ocean Infinity and QinetiQ, a reminder that undersea warfare is increasingly built on dual-use oceanographic technology.

Questions remain on detection ranges, vulnerability to trawling or tampering, and the practicalities of maintaining hundreds of small underwater vehicles in harsh North Atlantic conditions. SG-1 Fathom marks a clear shift in Western anti-submarine doctrine, away from a handful of exquisite platforms and toward attritable autonomous mass. If Atlantic Bastion delivers as advertised, the Royal Navy will gain something it has lacked since the Cold War: a persistent, scalable undersea tripwire that can watch far more ocean than any frigate screen or submarine patrol ever could.