Irish Navy plans to upgrade OPVs with towed array sonar

From 2027, for the first time, the Irish Navy will have the ability to detect underwater threats. Thales was contracted in June 2025 to supply three CATPAS-1 systems in a deal worth around €60 million (£51 million) with an option for a fourth system. The headline cost likely also covers integration into the OPVs, training, support, spares, associated combat system modifications, containerised handling equipment, processing suites and installation work.

The CAPTAS-1 is a containerised towed array sonar system, the smallest member of Thales’ CAPTAS family and is designed for rapid integration on vessels of opportunity. The system is typically housed in one or two standard TEU containers, containing the winch, handling system and processing equipment, with a total installed footprint of around 30–40 tonnes depending on configuration. 

CAPTAS-1 combines an active low-frequency source with a passive listening array, enabling detection of submarines at ranges of up to about 30km in favourable conditions, although performance is highly dependent on the acoustic environment. The processing software is continually improving and in the hands of trained operators, can be very effective. 

The system requires a crew detachment of around 3–5 operators and can be installed or removed within days rather than months. It is optimised for vessels displacing as little as 1,000 tonnes and operating at speeds typically below 12 knots during sonar deployment. Compared to larger systems such as CAPTAS-2 or CAPTAS-4, it has reduced detection range and tracking precision but offers a far lower cost and logistical burden, making it suitable for constabulary roles, EEZ monitoring and protection of subsea infrastructure.

The OPVs were not designed with ASW in mind and their own acoustic signature may limit effectiveness. Irish personnel will also have to undergo training and a steep learning curve as the service develops a nascent ASW capability from scratch. Even so, the systems represent a major step forward in Ireland’s ability to monitor activity in its Exclusive Economic Zone (EEZ).

The OPVs will also receive a new (unspecified) medium-range air search radar, electronic warfare systems and dedicated operations rooms. The OPVs receive support from the Irish Air Corps’ two C295W Persuader Maritime Surveillance Aircraft (MSA). These aircraft have an endurance of up to 10 hours and are based at Casement Aerodrome in Baldonnel, west of Dublin.

The Persuaders are fitted with a Light Detection And Ranging System (LIDAR) able to detect objects down to 25 metres below the ocean surface, but are being modified to deploy sonobouys from a rear door dispenser. The C295W carries the Fully Integrated Tactical System (FITS)  mission management software but it’s unclear if it can handle sonobouy data. CAPTAS-1 can be operated in multi-static mode to increase coverage by integration with sonobouys and other sensor arrays.

Despite these investments, identification remains a significant limitation. Detecting an underwater contact does not necessarily reveal its origin, meaning Ireland will continue to rely on cooperation with allies to classify potential threats. Lacking torpedoes, Ireland is also not yet equipped to engage or destroy contacts, but the initial objective is on detection and deterrence. By making hostile actors aware they are being monitored discourages interference with critical infrastructure and makes plausible deniability harder.

Ireland also plans to place fixed seabed sensors close to key to subsea infrastructure, feeding data into a new national maritime security centre and shared with European partners. This week, the UK and Ireland signed an updated Memorandum of Understanding (MoU) to enhance bilateral defence cooperation, focusing on maritime security, cyber defence, and critical undersea infrastructure protection.

From a UK perspective, any increase in ASW assets in the North Atlantic is to be welcomed. Given the desperate shortage of frigates, this also raises the question of whether the RN should consider purchasing lightweight sonars to enhance its Batch 1 OPVs or other vessels of opportunity as a matter of expediency.