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Receiving global success from a growing number of Navies (13 at this stage), the MU90 has become the reference LWT (notably within NATO) for the protection of naval forces deployments and maritime approaches.
Facing a grown perceived underwater threat, the MU90’s unique native performances still cope with all the submarines’ threats from Blue to Brown waters and meet the evolving ASW operational requirements, including midgets’ type submarines (manned or unmanned) hunting-killing capabilities in very shallow waters.
Evolving Anti-Submarine Warfare operational context
This ASW context evolution results from the cumulative effects of a global change and the current geopolitical instability on the one hand and from the increasing underwater threats on the other hand.
The geopolitical instability comes from increasing regional strains in Southeast Asia, especially due to the proliferation of submarines and competing territorial claims.
Concurrent with a high level of underwater activities revival on Europe’s eastern flank, this situation is fueled by the growing importance of the “Maritime Fact” with its control & exploitation stakes for the States (Economic Exclusive Zones, strategic passages & undersea infrastructures).
The increase of underwater threats mainly comes from the proliferation of conventionally-powered submarines (SSK & especially midgets), improving their own and their latest generation weapons performance.
While the current submarines’ order of battle is reaching almost 500 submarines among 40 Navies, the so-called Near-Peer competitors’ submarines are increasing in numbers.
New players are competing against the traditional leaders in export sales of submarines, performing continuous upgrades in the operating capability & performances of the submarines.
While globalization has made available to new players advanced stealth technologies, new designs benefit from the large use of COTS to minimize the time required to develop these systems.
These latest technologies are offering the submarines unprecedented stealth (quieting and coating techniques), endurance (propulsion improvements), and offensive capabilities through new computerized combat systems (sensors, weapons, and fire-control fully integrated), which results in greater tactical efficiency.
These factors are pushing the shift of the operational theatres towards naval operations in littoral and coastal areas, where the effectiveness of SSK (1 000t) and Midgets (< 500t) are maximized in shallow waters (and especially in choke points within strategic waterways), where they are tempted to exploit the restricted waters at their great tactical advantage, and willing to extend to the very shallow waters with the support of additional effectors, mainly unmanned vehicles.
Submarines are very well suited for asymmetric and hybrid tactics because they lend themselves to deceit and deniability. In particular for seabed warfare: the threat to strategic undersea infrastructures such as communication cables (Figure 1) and pipelines (Figure 2) has risen substantially, also because the number and criticality of these installations have increased, and will continue to do so.
As a result, the environmental conditions offer the submarines more opportunities to hide, mainly in shallow waters.
On one side, the environmental noise is increasing due to the increasing shipping traffic.
The United Nations Conference on Trade and Development estimates that roughly 80% of global trade by volume is transported by sea. Of that volume, 60% of maritime trade passes through Asia, with the South China Sea carrying an estimated one-third of global shipping. Real freeways for shipping have been established passing through a reduced number of strategic passages. As shown in Figure 3 (World Ocean Review, Living with the oceans, Published by Maribus, 2021), most of these chokepoints are located in South-East Asia vital artery of trade, within one of the world’s most contested waterways.
On the other side, the cumulative effects of global change, including climate change, increased population, and deeper industrialization have been intensifying the reduction of the quality of water.
Global climate changes are resulting in higher water temperatures and stronger stratification with consequent increases in propagation losses of the acoustic signals, and an increase in the density of phytoplankton further degrading the water quality and raising the reverberation index.
Overcoming the complex environmental conditions in restricted waters to defeat submarines
The operations in the littoral & coastal shallow waters environment are acting as a natural discriminator factor for the efficiency of any LWT.
Whereas these complex acoustic conditions are to be in favor of submarine operations, they simultaneously enhance the MU90’s operational performance superiority mainly in shallow waters, thanks to the high-grade features of its architecture.
Unlike competition, the MU90’s capability to engage targets in very poor acoustic conditions notably lies in the ability of the torpedo to:
- Carry out physical discern of the underwater objects by discriminating between bottom and bottomed target, mobile and stationary target, target and countermeasures (jammers & decoys);
- Allow confidence to increase with the tracked targets before proceeding to the final selection and attack.
The MU90 is the only LWT capable of a high degree of discrimination of real echoes in a noisy environment thanks to the pulse compression technique of the Frequency Modulation acoustic mode, particularly effective in detecting target highlights within the reverberation of the environment.
This capability is also useful against stationary targets hidden in the scattering. The characteristics of the scattering are highly dependent on the frequency of the emitted signal. Using a large bandwidth signal as the MU90 does, the peak effect of the scattering is spread with a reduction of the scattering amplitude.
In shallow waters, false alarms due to reflections on the sea surface or the sea bottom are frequent, but the MU90 has specific acoustic features and classification processes to identify and discard this type of false alarm.
When the target runs in confined areas such as fjords, estuaries or underwater canyons, some specific acoustic configurations increase the efficiency of the MU90 against the bottom and surface reverberation, using adapted thresholds and search pattern profiles.
The MU90 search depth will be close to the sea floor allowing the MU90 vertical beam-width, thus avoiding bottom reverberation detections. The MU90 detection range will be reduced to lower the possibility of false alarms.
These processes are based on the multisonar technique.
The MU90 makes use of five separate sonars orientable in different directions, operating in five frequency bandwidths; chosen maximizing the differences in propagation characteristics in non-isothermal conditions.
During the pursuit of a possible target in shallow water, the frequency difference technique is also used to increase the immunity from countermeasures and the capability of classifying the real target against the detections of the sea surface or bottom (false alarms).
This technique is based on the switching ping by ping of the sonar directed at the possible target.
The level of acquired noise or scattering is minimized by the MU90 making use of narrow beams with low levels of secondary beams.
The environmental noise in shallow waters has strong anisotropic components that can enter the acoustic head from all directions. When using narrow beams, the amplitude of secondary beams is generally increased, while the MU90 uses dedicated weighting algorithms to elaborate the contribution of the single transducers in the beam forming, minimizing the level of secondary beams.
The acoustic characteristics of the MU90 are handled by the Tactics software through an Alarm Reliability Manager.
The Tactics software assigns a reliability coefficient to every beam of the acoustic head in order to maximize the priority of the target detections in the directions with lower degradation or noise.
The MU90 undersea mission is carried out through a succession of logic states.
The progress in the succession of states is managed through many parameters resumed in a priority table.
In shallow waters, the MU90 is equipped with a Track Priority Management, specifically designed for these waters’ conditions. One of the most important parameters considered in the priority table management is the continuity of acquisitions and tracking.
In non-isothermal conditions, during pursuit guidance on both the vertical and horizontal planes is ensured in conjunction with bottom following & avoidance capabilities to maintain the possible target in the beam with the highest probability of detection.
All the features of the MU90 have been sea-proven by tests even in very demanding environmental conditions up to less than 50 m bottom depth, in the seawater stratification in front of river estuaries.
The MU90 is the only LWT with sea-proven ability to detect, classify, and attack any kind of submarine in a significant part of maritime approaches (near a rocky bottom and/or a cliff, hidden by the bottom reverberation) characterized by complex acoustic conditions (high environmental noise, high level of scattering and degraded acoustic propagation) encountered in littoral and coastal areas, archipelago, choke points, channels or straits.
As the underwater threat environment evolves and faces a growing likelihood of high-intensity warfare scenarios, the MU90’s unmatched sea-proven performances confirm its status as a deterrent weapon for the 21st century against the full spectrum of underwater threats, from ocean-deep blue waters to coastal very shallow brown waters.
