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As of May 9, 2026, Sweden’s Saab, the Defence Materiel Administration (FMV) and the Swedish Armed Forces have wrapped up the first sea-trial phase for the Large Uncrewed Undersea Vehicle (LUUV) demonstrator. The autonomous underwater vehicle is designed to give Sweden an uncrewed “first look” at hazardous parts of the Baltic Sea before crewed submarines, such as the Gotland-class boats, are sent into an area.
The LUUV program dates to a SEK 60 million contract awarded Aug. 29, 2025. The demonstrator runs on Saab’s Autonomous Ocean Core software and borrows heavily from Saab’s 7 m, 6.5-tonne Autonomous Ocean Drone (AOD) reference vehicle, which is rated for a range of more than 1,111 km at a speed of roughly 7.4 km/h.
FMV project manager Martin Nyqvist said the first phase is complete and that future trials will focus on autonomous functions, sensor behavior and operations in representative Baltic environments.
Sweden’s interest in a LUUV is not theoretical. Its three Gotland-class submarines—HSwMS Gotland, HSwMS Uppland and HSwMS Halland—entered service in 1996–1997 and still form the backbone of the country’s underwater operations. Each boat displaces about 1,500 tonnes submerged and is 60.4 m long, using Stirling air-independent propulsion for extended endurance. Two Blekinge-class A26 submarines, HSwMS Blekinge and HSwMS Skåne, are under construction and will add a new layer of capability.
The LUUV’s most likely early mission is route survey. Before a crewed submarine transits a narrow, shallow approach corridor, the uncrewed vehicle could move ahead to look for mines, seabed surveillance equipment, cables and obstacles. That preserves the submarine commander’s freedom to use the boat for missions that actually demand a submarine.
A crewed submarine doing a preliminary survey has to spend time on navigation, repeated sonar passes and transit. Every hour spent on that work reduces the time available for intelligence collection or other tasking. A LUUV mission does not have to cover every contingency, but it can clear many routes and leave the submarine outside the surveyed area.
There are limits. Buried mines, passive sensors and objects hidden by seabed relief—or simply outside the planned survey lane—can remain a threat after the autonomous vehicle has passed. Swedish planners seem to understand this; the LUUV is described as a risk-reduction tool, not a guarantee.
Because the LUUV’s own endurance and operating depth have not been disclosed, the most useful baseline is the AOD. Saab’s reference design is 7 m long, 1.4 m in diameter and weighs 6.5 tonnes. It uses lithium-ion batteries for a published range exceeding 600 nautical miles at 4 knots. At that speed, 600 nautical miles requires 150 hours—six days and six hours—which means the vehicle is being sized for missions lasting several days, not short hops.
Consider a plausible task: 100 nautical miles outbound, 300 nautical miles of surveillance, and 100 nautical miles back. That profile consumes 125 hours and leaves a nominal 100 nautical miles of battery range for reserves. If sensors or currents use more power, the margin shrinks quickly. The AOD also carries directional thrusters and an internal payload compartment with weight compensation, so it can deploy equipment as well as observe the seabed.
None of this means the LUUV demonstrator has demonstrated the same figures. Saab has not released validated endurance, depth, acoustic signature or sonar performance for the Swedish vehicle. The numbers are indicative, not confirmed.
The planned AOD/LUUV sensor suite appears designed for several jobs in one sortie. Multi-aperture sidescan sonar is intended to pick out mine-like objects, cables and unfamiliar equipment on or above the seabed. A multibeam echo sounder maps bottom contours. Forward-looking sonar helps the vehicle avoid running into obstacles while submerged. Flank-array and intercept sonars give passive acoustic awareness, potentially allowing the LUUV to detect submarines without emitting an active ping. DVL/IMU navigation provides position estimation without continuous satellite fixes.
That last point matters. The Baltic Sea is not satellite-friendly for submerged vehicles. Acoustic links are low-bandwidth and can reveal the vehicle’s presence. The LUUV will likely store high-resolution sonar imagery and pass it to operators after surfacing or recovery. For scheduled infrastructure checks, that is manageable. If a moving contact is detected, the delay between observation and delivery could make the information less useful.
The big open question is performance. Sonar detection ranges, operating frequencies, classification accuracy and false-alarm rates are all undisclosed. A sensor list on paper does not prove that the system can detect and track a modern diesel submarine in Baltic conditions.
The Baltic Sea is a hard place to hear anything. It covers 377,000 km², averages only 55 m deep and reaches 459 m at Landsort Deep. Shallow water, salinity gradients, seasonal thermoclines and dense shipping traffic all scatter sound. Sweden’s high-interest areas include Gotland, about 90 km offshore, and the southern approaches toward the Danish Straits. Critical submarine cables, power links and pipelines connect Sweden with Finland, Poland and the Baltic states.
Sabotage risk is demonstrated, not hypothetical. The September 2022 Nord Stream pipeline explosions and the October 2023 Balticconnector damage showed that underwater infrastructure can be attacked with no visible surface signature. A LUUV could be a useful tool for regular checks of selected cable and pipeline corridors. By comparing sidescan imagery over time, it might identify displaced objects, newly exposed cables, damaged installations or changes in the bottom contour.
Coverage math shows why detection quality depends on the sensor, not just the vehicle. If the LUUV runs 300 nautical miles of survey track and uses a 100 m swath, the nominal coverage is about 55.6 km². With a 200 m swath, that rises to 111.1 km². Real coverage will be less because overlapping track lines and maneuvering eat into the total. Still, repeated inspections of a defined corridor are feasible.
For a program to work without constant human control, Saab’s Autonomous Ocean Core provides four manoeuvring functions: Mission Manoeuvre for waypoints and payload actions, Vector Manoeuvre for precise positioning, Direct Manoeuvre for fallback control, and Position Hold for keeping the vehicle in a defined state. Safety is handled separately—Local Safety Mode supports supervised operation, External Safety Mode stops the vehicle after a communications loss, and Assault Mode allows fully autonomous missions without a continuous link.
The same software architecture has been exercised on Saab’s Enforcer 3.1 and 3.2 vehicles in San Diego and Sweden. But the Baltic imposes additional constraints. Without continuous satellite connectivity and with limited acoustic bandwidth, the vehicle has to be trusted to execute long segments of a mission on its own.
Sweden also wants to know whether a future LUUV can operate from the Blekinge-class submarines. Both HSwMS Blekinge and HSwMS Skåne are being built with a Multi-Mission Portal intended to handle divers, equipment and autonomous vehicles. The AOD’s size was chosen with an eye toward possible submarine compatibility.
Rear Adm. Fredrik Lindén, FMV’s director of naval systems, said in March 2026 that the LUUV demonstrator would be used to establish requirements for future A26-compatible drones. That is a separate challenge from shore-based operations. Submarine deployment would require qualified launch and recovery procedures, safe separation, submerged rendezvous, precise relative navigation and a recovery sequence with enough battery reserve left to be useful.
Shore or surface-vessel deployment avoids most of those problems, and the LUUV’s payload compartment could accept temporary seabed sensors, adding a layer beyond reconnaissance. Weapons, however, are explicitly out of scope for this first Swedish development phase.
The SEK 60 million award is a development contract, not a production price. No procurement quantity, operational requirement for submarine recovery, or service-entry date has been announced. The LUUV is best seen as a technology demonstrator that will help Sweden write requirements for a future system.
The program is running in parallel with NATO’s increased attention to the Baltic. Sweden joined NATO in March 2024. NATO launched Baltic Sentry in January 2025, and Task Force X-Baltic tested 70 aerial and maritime drones between March and October 2025. A LUUV would complement those efforts by inspecting underwater infrastructure and collecting acoustic information that radar, aerial sensors and shipboard Automatic Identification System data cannot provide.
Saab’s AOD is smaller than the U.S. Navy’s Orca XLUUV or Australia’s Ghost Shark. The closest analogue may
