Countering the threat from autonomous underwater vehicles

In this guest article, Kamil Sadowski considers how navies may employ surface platforms to counter the evolving threat from UUVs.

There are many Autonomous/Uncrewed Underwater Vehicle (UUV) programs either in development or available today for both military and non-military applications. At present the majority of operational naval UUVs are employed in mine warfare or hydrographic survey roles. Many navies have much greater ambitions to operate larger more complex XLUUVs (Such as the RN’s CETUS programme) for maritime reconnaissance and eventually for strike missions.

UUVs can provide stand-off extension of sensors and effectors for crewed vessels, can operate in high-risk environments and tolerate very close interactions with adversary assets. Host platforms for large UUVs may include submarines, warships or direct launch from ashore.

AUUVW

UUVs are starting to pose a considerable new threat that presents challenges for conventional Anti-Submarine Warfare (ASW) operators, methods and systems. At the end of the Cold War, the operational focus shifted from ocean to littoral and shallow water environments. This change required ASW forces to evolve to deal with stealthy diesel-electric and AIP submarines in an unfavourable environment for detection. UUVs, mainly operating in the same littorals will add another layer of complexity to the challenge.

For the RN, UUVs may offer a relatively rapid way to bolster its slim underwater forces but adversaries are in a race to do the same and there is an urgent need for effective countermeasures. The threat to crewed submarines from UUVs is worthy of another article but here we will focus on ways of countering them from the surface. This kind of warfare could be characterised as a new sub-genre of ‘Anti-UUV Warfare’ (AUUVW) against small, difficult-to-detect platforms that will need specific systems to counter them.

Situational awareness

Effective surveillance is essential to ensure the successful execution of most kill-chain phases (detection, classification and tracking). Most of the ASW sensor and weapon systems in service today are optimised for manned submarine targets. The new generation of acoustic sensors known as Low-Frequency Active Sonar (LFAS) delivers high performance and has made significant advances in detecting ultra-quiet AIP submarines. Networked multi-static sonar is another area where there have been improvements in detection capability. UUVs and even XLUUVs generally have low target strength, especially in bow-aft aspect and a minimal radiated noise signature. Detection in littoral waters will therefore be especially problematic with short detection ranges allowing very little time to react and deploy countermeasures.

For now, it can be assumed most UUVs will be employed on ISR missions with endurance and payload requirements dictating their size. On detection, classification and assessment of the size, type and role of a UUV will also be problematic. Many operations will now have to assume adversary UUVs may be present, even if they cannot be detected. Only observed crewed submarine activity, ORBAT analysis and a wider intelligence picture may give clues to the scale of the threat.

Threat neutralisation

The difficulties of neutralisation is second only to the problems of detection. The threat may be countered, at least partly, by manoeuvre but this is possible only with good situational awareness and a valid tactical picture. Most surface assets will have a very significant advantage over UUV’s in terms of speed but in many potential warfare scenarios, manoeuvre alone is not enough, especially during protection of stationary objects such as undersea infrastructure.

A cost-effective anti-UUV effector should be considered a key near-future requirement as existing ASW weapons are both ill-suited and very expensive. The current generation of air or surface-launched lightweight torpedoes is the primary ASW weapon of today but they lack adequate sensors and guidance systems to localise and kill UUVs. A more appropriate counter-UUV weapon would be mini-torpedoes. This new class of torpedoes will provide a low-cost solution with the appropriate manoeuvrability, sensors, speed and warhead optimised to destroy targets up to XLUUV size.

An alternative to exquisite mini torpedoes is rocket-propelled depth charges. They provide sufficient range, firepower and are more affordable. The Russians and some former Eastern Block nations still have warships armed with these virtually obsolete ASW weapons but they may have found a new role. Standard gravity depth charges are rarely used today but may also offer a promising solution. A new generation of smaller depth charges is required as conventional DCs are heavy and ill-suited for deployment in numbers from small USVs or aerial vehicles. BAE Systems‘ New Generation Depth Charge concept is one solution currently in development.

The diagram below provides a summary of surveillance and neutralisation factors with a short comparison between typical ASW and near-future AUUVW. Both areas have much in common in terms of sensors and effectors but with significant differences and restrictions concerning detection probability and weapon employment.

Conclusion

There are a wide variety of programmes to develop uncrewed and autonomous systems for use in conventional ASW  but AUUVW appears to be a lower priority. This may soon change in the face of proliferating UUV programmes and the development of submersibles with increasing range, sensor and AI capabilities.

It is highly possible that in future ASW missions, countering XLUUVs will be the first objective. In other scenarios, the same asset will be deployed to probe adversary areas of operations or their territorial waters and AUUVW may assume the same level of importance as ASW today. Stand-off operations with both sides employing autonomous or uncrewed systems make USVs and aerial platforms natural candidates for AUUVW missions.

Kamil Sadowski served as an officer in the Polish Navy for 21 years specialising in ASW and has experience of developing and deploying underwater weapons systems.