Development of unmanned torpedoes for submarine combat operations [Part 2]

The development of unmanned rotors in ZOP operations is increasingly focused on the integration of advanced sensors and new compact effectors. Mass and energy limitations of pilotless platforms force the search for lighter solutions, such as miniature sonars lowered, non-acoustic sensors or very light means of destruction.

In the first part, I described the importance of unmanned centrifuges as carriers of sound surveillance sensors, with particular emphasis on radio-hydroacoustic buoys and limitations resulting from passive analysis. I also pointed out that despite the dynamic development of data processing tools, the effectiveness of these solutions still determines the reality of the operating environment and the complexity of the detection process. This naturally directs attention to active sensors, in particular abandoned sonars, which in the aviation of the ZOP have remained a tool with the highest target location potential for years.

Light sonar lowered

Abandoned sonars, which are currently used by ZOP marine helicopters, due to the weight and energy demand, are not suitable for integration with most pilot-free rotors. The total weight of the complete device (antena, winch and electronic block) is about 270 kg for compact variant (e.g. AN/AQS-13/18 family) or 300-350 kg for systems with the highest potential (like Thales FLASH, Raytheon AN/ASQ-22 ALFS, DS-100 HELRAS).

Sonar is lowered with the highest potential sensor in the entire range of ZOP acoustic sensors and the presence of this device on board the helicopter, from the point of view of the ZOP tactics, is treated in similar categories as sonar towed on the ship.

On one of the visualizations of the British PROTEUS program, you can see the station leaving in the recess of the task section. The type of this device is unknown, probably one of the lighter solutions (e.g. AN/AQS-13/18). On the other hand, if this vision is fulfilled, PROTEUS will probably be the world's first RUAS equipped with such a sensor.

PROTEUS taskroom with sonar lowered

The rationale of developing a compact solution for lightweight unmanned aircraft platforms has not escaped the attention of experts and the work on its creation is under way. An element of one of the greatest challenges is the kablo-line and its winch, which represent a significant part of the total mass of such module. As a result, one of the concepts considered was a hybrid device, based on PRHA elements and technology, using an unrecoverable, cut-off transducer. The lack of a winch, however, saves a lot of weight and energy, so that the solution described in the assumptions promises as a module even for the lightest RUAS.

The use of PRHA as a base element is a promising direction (especially for light carriers) due to the size, mass, relatively low energy demand and a number of ready-to-adapt elements such as acoustic sensor (which occurs in several variants) and electronic block (which includes preliminary processing of acoustic signals with a communication module). Therefore, using these elements to build a new, light sonar abandoned may have significant cost-effect potential. The design would require power (instead of battery) and a seemingly simple element, which is a cablo-line winch.

Adaptation of active PRHA elements to compact lowered sonar (no scale drawing)

Given the wide range of PRHAs of NATO standard, even in such a compact solution, it is possible to scale the sensor's potential, by choosing between variants based on the standard PRHA (e.g.DIFAR/HIDAR, DICASS) and high potential buoys (e.g. Thales SonoFLASH). However, the choice of the latter involves the need to develop another missing functionality in PRHA, which is the mechanism of folding/distributing an antenna with a level of scalable complications to desired detection ranges.

Analysis of antenna variants abandoned on the basis of available solutions in the PRHA range of NATO standard would require separate development. No less, equipped with such sonar abandoned RUAS in practice would function as a "mobile PRHA", which at the same time simplifies the course of submarine surveillance. This process would be controlled by another already existing component, the acoustic processor on a manned aircraft, ship or station on land.

Non-acoustic sensors

Acoustical surveillance remains the main method of surveillance for the search for submarines, but technological developments have also allowed the development of compact, non-acoustic sensors, supporting awareness of the situation in the activities of the ZOP. Many of these devices are created ultimately for installation on light unmanned units, with low mass and energy demand. In the growing group of these devices are, among others, radio-location and electro-optic sensors.

Light RUAS (250 kg MTOW) type AW HERO. Visible replacement modules of the nasal part including (right) radar with raster antenna

Larger constructions such as VSR-700 (Airbus) mean less compromises allowing, for example, the installation of a larger range radar and with an antenna of indoor observation

While they actually play an important role in the activities of the ZOP, the environment is definitely not their leading domain. The magnetic anomaly detector called MAD (Magnetic Anomaly Detector) is a non-acoustic sensor dedicated to this role.

MAD often associated as gradually disappearing in the modern forces of the ZOP relic of the Cold War, despite all appearances is still a respected sensor, providing information of high reliability. The narrow surveillance belt that MAD covers allows effective use of it mainly to search a small sector (e.g. after noise-measurement or ESM emissions), as a contact confirmation tool. No less, the detection thus obtained ensures high precision of target location and plays a significant role in the contact classification process.

CAE MAD-XR

Compared to the existing detectors, the next generation MAD-XR equipment weighs 1,5 kg (instead of 25-30 kg of the previous generation device), with the same sensitivity parameters. With regard to most manned aircraft, the solution does not generate colossal savings, but in the case of unmanned platforms, where every kilogram and every element requiring power supply counts, the situation changes dramatically.

Effector

In the current development programmes of unmanned aviation, ZOPs, the capability of destruction plays a secondary role or fall to the background. The awareness of the situation shall be regarded as a priority as a condition necessary to take any risk avoidance or neutralisation reaction. Despite this, work has also been undertaken on the capability of destruction, which can be divided into two directions for unmanned systems:

• adaptation of the unmanned unit to carry already existing weapons types (such as light ZOP torpedoes),
• development of a new compact effector that can be carried by light units.

Joint project BAE Systems and Malloy Aeronautics: T-600 demonstrator with suspended light ZOP torpedo type Stingray

It is difficult to say clearly about the dominant direction. With regard to the evolving opponent, work is underway on new generation effectors capable of meeting today and the future realities. In addition to the classic purpose of the ZOP's submarine operation, the new threat group begins to be autonomous submarines, in particular those belonging to the XLUUV class (Extra-Large Unmanned Underwater Vehicle).

This problem exists today, and the number of XLUUV development programs in the world shows a rapid increase in its scale in the near future. In addition, modern ZOP armaments, based mainly on light torpedoes of 324/400mm, do not adhere to such objectives due to the way the guidance system operates and, above all, the economic factor. The exception to this is still the use of "classical" deep-sea bombs or rocket deep-sea bombs (e.g. RBU-6000 on KozOP ORP "Kashub").

For the above reasons, work has been undertaken on solutions dedicated to this new category of targets, some of which are also expected to be an effector capable of integration with light flying platforms. Examples of new directions are, for example, very light VLWT torpedoes (Very Lightweight Torpedo), which are a new category in the ZOP range of effects and a new generation of deep-sea bombs.

Black Scorpion – very light torpedo (VLWT)

The CVLWT initiative developed by Northrop Grumman was to be widely applied in the new realities of the ZOP. Problems with the work on the countertorpedial variant CAT (Countermeasure Anti-Torpedo) have, however, negatively affected the pace and scope of implementation of the programme.

In parallel, other attempts are being made to distinguish the category of very light torpedoes (VLWT), including constructions based on earlier projects that faced integration difficulties and problems with achieving the assumed low-cost. Despite these limitations, promising tests have been carried out to integrate selected effectors into unmanned platforms, including MQ-8C rotors.

Northrop Grumman – Common Very Lightweight Torpedo (CVLWT)

These examples of new effectors have a very limited impact when the target is a submarine, mainly due to light warheads and low speed, as with very light new generation torpedoes. Some of these structures are developed as another attempt to separate the category of VLWT, with previous initiatives faced significant integration problems and difficulties in achieving the assumed low cost. Despite these limitations, these systems remain an adequate means of combating unmanned underwater vehicles, and the key factors determining their success will be combat efficiency and as low a cost as possible.

View models of the new generation of deep-sea bombs and their air tank

RUAS-ASW programmes

Marine variants of MQ-8 helicopters in versions B and C have more than 10 years of operational experience in the U.S. Navy, each based on a different base construction of the rotor. The original purpose of these machines was to indicate targets and to support the identification of the water situation. For MQ-8 helicopters, it was also planned to develop modules for the detection of marine mines, but with increasing interest in the wider scope of use the concept of their involvement in the tasks of the ZOP emerged. This initiative was a natural direction of development, inter alia due to the parallel use of MQ-8 alongside MH-60 Seahawk on-board helicopters, which are one of the pillars of the U.S. Navy's ZOP capabilities.

MQ-8C Sea Scout aboard US Navy vessel

On the exposed materials you can see the MQ-8C, carrying two PRHA trays, containing 24 "G" size units (photos from the sea trials can actually see a discharge of the "G-size" buoy), but there is no information about the final direction of development. The choice of the PRHA of the size of the "G" would mean aiming to carry a significant number of buoys (48 units with two trays), but at the moment it cannot be excluded that future solutions common to MQ-8 and MQ-9B SeaGuardian will also be developed.

Visualization of MQ-8C with two SMP (Sonobuoy Mission Pod) tanks developed by Ultra, the largest PRHA manufacturer currently. The company offers scalability of its solution for different host sizes.

Like the U.S. Navy, the United Kingdom's naval aviation also focuses on large platforms. This is a clear analogy to the concept of using heavy-duty ZOP AW-101 Merlin helicopters adopted in the Royal Navy, which are distinguished by the combination of high combat potential and long-term flight. In view of these features, corresponding to British operational requirements, AW-101 Merlin remains the only type of helicopter used in the Royal Navy for ZOP tasks.

However, the scale of operational needs exceeds the available resources of each Navy, which led to the launch, in cooperation with Leonardo, of the pilot-free program PROTEUS. In parallel, the company also develops smaller unmanned platforms from the same family of solutions, but without the declared focus on the tasks of the ZOP. The PROTEUS presented visualizations show a modular hull structure with a separate task section, allowing adaptation to the ZOP missions, including integration of radio-hydroacoustic buoys and signal processing blocks.

RUAS PROTEUS – visible task section

The potential for adaptation of the described viroplane is not only a significant addition and support (e.g. through interaction with AW-101 Merlin) for the sea aviation of the ZOP UK Royal Navy, but also offers the possibility of introducing the capabilities of the ZOP on board, for example, non-capacity units. In the UK Royal Navy, for example, T31 frigates are currently being built, based on the same as program MIecznikProject ArrowHead 140.

A representative of the mid-group MTOW 500-700 kg, VSR-700 in 2022 passed a number of qualifying tests on French MW ships. The choice of platform of this size is an interesting solution, combining compact design with a wide range of combat capabilities. In 2023, the ability to adapt to the tasks of the ZOP, developed in cooperation with Thales, was presented. The PRHA module, which includes the functions of discharge, reception and signal transfer, allows to operate with 4 units of PRHA size "A-size". This element is related to the development program of the new generation of PRHA, the high potential of SonoFLASH (Thales), which enters service in the Navy of France.

VSR-700 presented at Euronaval 2024. Onboard visible PRHA tank and light deep-sea bombs and next to the four-chamber PRHA tank of the A-size family (manufacturer explores different solutions)

In the opinion of Airbus, the solution proposed by the company represents a very beneficial compromise between the launch mass of the platform and the load taken and the long-term flight. In the comparison presented, all three of the above categories were confronted:

The S-100 Camcopter provides a flight duration of up to 6 h with a load of 34 kg (source: Schiebel), while the MQ-8C Firescout can operate up to 12 h with 136 kg of cargo (source: Navair). By comparison, VSR-700 is capable of 10 h long-term flight with 100 kg of cargo.

The compatibility of these arguments reflects several other schemes. An example is Schiebel, who also intends to be present in this sector with the latest S-300 (660 kg MTOW), a larger "brother" of popular S-100 Camcopter.

Schiebel S-100 against the background of the larger S-300

The Schebiel family of helicopters is probably connected with the largest variety of solutions that can now be observed among the ZOP task modules dedicated to unmanned viroplanes. This applies to both the popular S-100 Camcopter and its larger "brother" S-300. As with the described VSR-700 (Airbus), in the considerations on configuration of the S-300 to the ZOP, the revealed materials depict two variants of the PRHA discharge system: 8 x A-size or 12 x G-size.

The pilot-free payloads of the lightest group, i.e. weighing 200-250 kg (MTOW), also join the range of potential ZOP units. The inspiration for this initiative was, first of all, that the helicopters described, entered or now enter service in the naval forces and the results of analyses that showed that it was possible to extend the scope of their tasks to include this area. For obvious reasons, the challenge is the weight of the load taken (45-50 kg), the supply of which even in the case of PRHA of size "G", is rapidly exhausted. The transfer of PRHA of the "A-size" family, in particular active ones weighing more than 15 kg, with such a low load capacity is very difficult.

On demonstrators based on Schiebel S-100 and UMS Skeldar V-200, PRHA launchers were used to carry 4 or 6 "G" buoys respectively. Mass limitations forced the separation of PRHA drop-off and receiving/signing function into two aircraft (as in the pictures below). Named helicopters in the ZOP variant since 2022 have been participating in the REPMUS exercise (Robotic Experiment and Prototyping using Maritime Uncreated Systems).

One of the interesting ideas that are being studied in the case of S-100 is the drop for a single PRHA size A. Due to the weight limits of the cargo described above, it was unlikely even considering the possibility to prohibit these buoys. No less, despite the number limited to just one piece, this solution is not meaningless. Reaching the PRHA of the A-size family is a result of cooperation with Thales, which develops its own, high potential buoy SonoFLASH. The potential of this new generation of PRHA (especially in multi-static network activities) is the reason why the S-100 in the picture below is likely to be used in future ZOP operations.

Unmanned payments in the POP support system

Unmanned aircraft systems have a certain future in ZOP operations. The aim of the development of these systems is not to displace manned units, this is not at least the current perspective. The process of implementing non-pilot units goes hand in hand with research on the concept of action alongside "classical" forces as their support element.

The element combining most of these RUAS adaptation programs to the tasks of the ZOP are PRHA with a differentiated approach of their contractors to adapt this capacity. This applies primarily to the size group and the number of buoys taken aboard. Due to the nature of mass use of PRHA, the quantity of activities is and will always be the dominant factor. On the other hand, the leading idea of operational use of described unmanned systems is to act as an element of support.

An example is the interaction with, for example, manned MPA, where the role of an unmanned unit can be to extend the monitoring time set by the MPA patrol aircraft of the buoy field, keeping a small stock of buoys to confirm contact. Another example may refer to the ZOP's operations involving interacting with its own submarine forces, which are demanding from the point of view of coordinating forces in the upper and lower half-spheres. The ability to quickly establish even one-sided communication with its own submarine is particularly important to maintain the situational awareness of the forces. This capacity plays a particularly important role in the need for weapons associated with the implementation of WSM (Water Space Management) procedures necessary for the effective and safe use of the ZOP countermeasures when its own submarine is in the vicinity of the enemy.

The vision of the interaction of the frigate Swordfish with the Orca submarine – the communication PRHA allows unilateral data transmission for the coordination of forces

In conclusion, the participation of the lightest of these units in the activities of the ZOP cannot be explicitly cancelled. The fact is that, for example, the number of PRHAs taken will determine the potential and scale of the unit's involvement in the ZOP missions.

Although none of the currently developed RUAS systems in the ZOP configuration have yet reached operational readiness, they are part of the development of modern naval forces. Thus, they are a worthy further component for the frigate Swordfish, not only for the very reason of the lack of an on-board helicopter. First of all, the role of RUAS is not limited to the main area in which the article is focused. Task modules such as compact radar or electrooptic heads make pilot-free on-board payloads as valuable units supporting the marine situation recognition process and identification and indication of targets at ranges Beyond the horizon.