IN Brief:
- Mitsubishi Heavy Industries has selected OKI to supply towed passive sonar systems for Australia’s first three new frigates.
- The contract is OKI’s first overseas defence-equipment transfer within an 11-ship Australian programme.
- Production will require alignment across sonar hardware, handling machinery, processing, ship integration, training, and long-term support.
OKI has secured a contract from Mitsubishi Heavy Industries to supply towed passive sonar systems and associated equipment for the first three improved Mogami-class frigates ordered by Australia.
The agreement represents OKI’s first overseas transfer of defence equipment and places Japanese underwater-acoustic technology inside one of Australia’s largest naval construction programmes. Eleven frigates are planned, with the initial vessels to be constructed in Japan before production moves to Western Australia.
A towed passive sonar is not a self-contained sensor fitted late in ship construction. It combines an acoustic array, tow cable, handling machinery, deployment and recovery controls, processing electronics, software, operator consoles, and interfaces with the ship’s combat-management system. Performance also depends on where the equipment is installed and how effectively machinery and flow noise are controlled.
The first three ships will establish the technical baseline that Australian construction must later reproduce. Differences in cable routing, deck machinery, electrical supply, cooling, hull structure, or combat-system configuration could affect installation and testing, so the transition between Japanese- and Australian-built vessels will require tightly controlled design data and a stable configuration.
OKI has more than nine decades of experience in underwater acoustics and supplies sonar-related equipment for Japanese naval applications. Exporting that capability creates additional obligations across documentation, training, maintenance procedures, spare-parts planning, repair authority, and long-term software support.
Sonar performance begins in the shipyard
Passive sonar depends on detecting weak acoustic signatures against a noisy background, which places strict manufacturing requirements on hydrophones, cable connections, array geometry, electronic channels, and signal-processing hardware. Small variations can reduce sensitivity or introduce noise that is difficult to distinguish from the operating environment.
The handling system creates a separate engineering burden because a long array must be stored, deployed, streamed, recovered, and protected in difficult sea conditions. Winches, fairleads, tow points, tension controls, and cable-management equipment must withstand repeated cycles without damaging sensitive internal conductors. The installation also occupies valuable volume in the stern, competing with aviation support, boats, weapons, and other mission systems.
Ship integration must minimise interference from propulsion machinery, pumps, generators, and turbulent flow. Since the improved Mogami design is intended to operate with a relatively small crew and extensive automation, deployment, monitoring, and fault handling cannot depend upon a large specialist team. Automation must reduce workload without concealing equipment condition from operators and maintainers.
Australia’s decision to construct later ships domestically adds a substantial technology-transfer requirement. Australian yards and suppliers will need access to installation tolerances, alignment requirements, cable specifications, test procedures, and acceptance data. Engineers must also know which items can be produced or repaired locally and which will continue to come from Japan.
The arrangement could establish Australian capability well beyond the initial ship build. Towed-array support requires specialist work in acoustic calibration, electronics repair, cable handling, software maintenance, and at-sea testing. Locating those skills domestically would reduce overseas turnaround times and give the Royal Australian Navy greater control over fleet availability.
Japan’s wider naval export strategy is already placing domestic designs into programmes where local construction and support are decisive. Its Mogami and submarine offer to Indonesia similarly combines platform supply with questions over technology access, maintenance, and domestic industrial participation.
Australia will provide a more immediate test of whether Japanese equipment can be transferred without losing configuration discipline. Sonar is particularly sensitive because processing methods, performance data, and acoustic libraries remain closely controlled, leaving security arrangements intertwined with production and support.
The first three vessels will serve as learning ships, establishing how Japanese equipment, Australian requirements, and the selected combat-system architecture work together before domestic construction begins. Problems discovered after Australian production starts would be far more expensive to correct across two shipyards and several supplier bases.
Long-term obsolescence will require joint management because processors, storage devices, electronic components, and software dependencies change much faster than a frigate’s service life. OKI and MHI need planned upgrade routes that preserve acoustic performance without repeatedly redesigning surrounding ship interfaces.
Australian industry will also need qualified test equipment and representative shore facilities. Diagnosing a fault at sea without the ability to reproduce it ashore increases repair time and can force complete modules back to the original manufacturer. Domestic support therefore depends as much on data and instrumentation as on spare hardware.
Although the initial contract covers three shipsets, the selected sonar baseline will influence all 11 frigates. It will shape stern design, electrical services, combat-system integration, crew training, maintenance infrastructure, software support, and underwater-warfare capability throughout the fleet.
