Dutch/Belgian Anti-Submarine Warfare Frigates to carry Ultra sonar

Ultra Maritime announced a C$200 million  (€124 million/$148 million) contract to supply a sonar suite for anti-submarine warfare (ASW) to the Royal Netherlands Navy and the Belgian Navy on June 26th. This system will be integrated into the navies’ new Anti-Submarine Warfare Frigates, providing enhanced capabilities for detecting submarines and torpedoes in diverse maritime environments, from deep water to coastal areas. 

The core of Ultra Maritime’s offering is the Low-Frequency Active Passive Sonar (LFAPS) system. This system combines Ultra Maritime’s Sea Lancer in-line and Sea Sabre towed body variable depth sonars (VDS). The Sea Lancer features an in-line Horizontal Projector Array, a unique design that works in conjunction with a conventional towed body to optimise performance and flexibility across various operational theatres, according to Ultra Maritime. This combination is designed to detect even the quietest submarines, the company states, which will be key for anti-submarine warfare frigates. The system also incorporates advanced health monitoring algorithms, which are designed to enhance operational performance and user operability, thereby reducing through-life costs.

Delivery of the frigates is expected between 2028 and 2032, with the first frigate for the Royal Netherlands Navy scheduled for 2029 and the first for the Belgian Navy in 2030. The Anti-Submarine Warfare Frigates project is led by the Netherlands, with Damen and Thales acting as prime contractors. Once in service, they will replace the current M-frigates (Karel Doorman-class). 

They are designed to operate as quietly as possible, which is crucial for effective submarine detection. To that end, the frigates will be fitted with the Kongsberg Controllable Pitch Propellers, which are reportedly quieter than most alternatives. The frigates are also set to be fitted with BAE Systems’ Bofors 40 Mk 4 naval guns and will accommodate an NH90 helicopter, extending their ASW and surveillance range. 

Further enhancing their maritime capabilities, the Netherlands and Belgium have signed an agreement to improve the effectiveness of their naval forces and collectively address ongoing challenges, including countering Russian aggression at sea and supporting Ukraine’s defence. This intensified cooperation, formally agreed upon on 19th June, by Dutch Minister of Defence Ruben Brekelmans and his Belgian counterpart Theo Francken, extends to jointly purchasing and coordinating maritime equipment. The press release observed that both countries have a range of defence industry capabilities that could be beneficial to their mutual defence. 

The Lobster sea drone undergoing tests at sea. It is the type of capability that could be integrated onto the the Dutch and Belgian anti-submarine warfare frigates. Credit: Dutch MoD

In another ASW related development, the Royal Netherlands Navy and a company called Lobster Robotics, announced a collaboration to develop a military version of the “Scout” underwater drone, on 24th June. This initiative falls under the Rapid Adoption Action Plan (RAAP), a special project intended to quickly deploy new technologies for NATO, and was sealed during the NATO summit in The Hague. The Scout drone is designed to clearly visualise, identify, and classify objects on the seabed, according to the Dutch MoD.

State Secretary Gijs of Defence Tuinman highlighted how this project exemplifies the direct application of civil innovation by the armed forces, emphasising that “Dual-use technologies such as the Scout make us faster, smarter and more effective. Within NATO, we jointly strengthen our technological advantage and operational strength.” Lobster Robotics was an early participant in NATO’s DIANA (Defence Innovation Accelerator for the North Atlantic) innovation programme, successfully completing it in February. The project is a collaboration between various defence units, including the Front Innovation Centre and the Defence Diving Group, with the Netherlands sharing knowledge and experiences with other NATO organisations and countries.

There is increasing cross-pollination of civil technology into the maritime domain, especially for ASW. This is in part because a lot of autonomous civil technology for mapping the seabed already exists, allowing the ready conversion of those systems into a similar capability for defence. For example, Helsing recently unveiled the SG-1 Fathom which leverages an existing underwater glider and an artificial intelligence (AI) system for undersea surveillance called Lura.

Understanding towed array sonar

A towed array sonar system is crucial for modern anti-submarine warfare. It consists of a long cable, equipped with hydrophones (underwater microphones), that is towed behind a ship. This design allows the hydrophones to be positioned away from the ship’s own noise, significantly improving the system’s ability to detect faint underwater sounds. The LFAPS system utilises both active and passive sonar principles. In passive sonar, the system listens for sounds emitted by submarines, such as propeller noise or internal machinery. Active sonar, conversely, emits sound pulses (pings) into the water and then listens for the echoes that bounce back from objects, including submarines. The combination of these active and passive capabilities, along with the extended reach of a towed array, allows for comprehensive detection and tracking of underwater threats across various depths. However, it is effectively limited to the area that the ship can patrol – more ships means more sea that can be patrolled.

Calibre comment

Sonar is at an interesting juncture as a technology. It has undergone multiple improvements in the past three decades which make it more capable than ever before, but remains reliant upon the skill of the operator and their ability to recognise sounds. This is set against an increasingly busy sea with more sounds and ships than ever. So, sonar is one area in which AI can extract significant improvements in performance at relatively low risk. It is not clear if the Dutch and Belgian anti-submarine warfare frigates will include any AI, but it is something that can be relatively straightforward to install at a later date. 

By Sam Cranny-Evans, published on 1st July, 2025. Credit for the lead image is the Dutch MoD, it shows an artist’s render of the Anti-Submarine Warfare Frigates.