AWD - the anti-submarine warfare requirement
The term Air Warfare Destroyer is probably too narrow to encompass the roles the RAN's new surface combatant will have to fill; anti-submarine warfare will be a key role for the new ship, argues one expert.
The RAN surface combatant force provides the ADF with considerable flexibility to provide Australia with an appropriate response mechanism across a wide spectrum of threats to the country's maritime interests. However, in recent times many naval experts contend that the force has suffered constant erosion in its relative level of capability, particularly at the higher ends of naval warfare.
Under such circumstances concern grows that the ships cannot successfully complete the missions expected of them and that something needs to be done to restore capability in an important force element group. To some extent the upgrade programs being undertaken for both the FFGs and the Anzac-class frigates (FFHs) is a welcome and necessary step along the road to correcting the problem but the capability potential of these ships is finite. The preferred solution is, of course, to acquire new ships. Consequently, the planned acquisition of at least three Air Warfare Destroyers (AWD) [which was confirmed by the Minister in November 2003 - Ed.] represents the best opportunity for the RAN to significantly enhance its maritime warfare capability.
>From a strategic perspective, the AWD is openly described as providing a sea-control capability that will be expected to guarantee not only access to the region's strategic maritime areas but also to maintain freedom of manoeuvre for the ADF within these regions over extended periods of time. The vision is to provide a level of capability several orders of magnitude greater than that which could possibly be achieved with today's surface combatants. Against that backdrop of significant enhancement of Australia's maritime warfare capability the requirement for the AWD conjures up impressive images. Aegis Combat Systems, phased array radars, advanced ECM/ESM, SM-2 (and perhaps in the not too distant future SM-3) missiles and a plethora of tactical data links that may include CEC capability are all being advocated for inclusion.
Ultimately, if this grand vision is realised the AWD will possess considerable AW power. However, this is a ship that will have to operate in a multi-threat environment in a region where very capable threats other than fast jets are being acquired at an impressive rate. Moreover, these threats are virtually all classic sea-denial capabilities designed to limit the potential of marauding hostile forces conducting operations close to home. In that sense the absence of discussion of Underwater Warfare (UWW) requirements is disturbing. There seems little point in possessing such an impressive AW capability if it cannot establish the degree of freedom the ADF needs in order to undertake missions in support of Australia's national interests.
The regional air threat is well known and documented. On the other hand the regional submarine threat, although well documented, seems less understood. The rapid emergence of very capable conventional submarines being operated close to their home ports in water where local knowledge is high is a threat, with the capability to deny access and freedom to the RAN at least as potent as the regional air threat. And yet there is precious little public acknowledgement of the need for considerable levels of ASW capability. Admittedly, there have been announcements that the AWD is more than just an AW platform and that the ASW capability will be an evolution from existing capabilities and systems. However against the grand statements about AW capability, this is marginal at best. That said, an analysis of the submarine threat readily translates into a coherent statement of requirements, which points towards the technology needs of the AWD.
The modern conventional submarine has massive potential, hence the investment Australia has made in the Collins class. This concept has not been lost on regional nations, many of which are embarking on acquisition programs to obtain submarines at least as capable as Collins. Submarines such the German 212, Russian Kilo and French Skorpene are becoming attractive to those navies wanting potent sea-denial forces. Equipped with excellent sensor suites, modern weapons and designed for maximum stealth, these submarines are a formidable threat. Moreover, when operated competently in the congested and complex waters of the region they become the most difficult threat the AWD will have to deal with. In comparison the air threat seems almost easy to cope with!
Existing operational doctrine and tactical procedures fundamentally drive the UWW capability requirement. At the most basic level, surface combatants potentially possess the capability for both self defence and force protection. In all circumstances ships must have self-defence capability and this can be thought of as the means to counter hostile submarines as they close to attack the ship and the ability to deal with the submarine's weapon of choice, the heavyweight torpedo, once it has been fired. In addition to ASW self defence some ships must possess the means to undertake force protection. This can be defined in the context of generating sufficient levels of ASW tactical surveillance to ensure that the force is warned of the presence of a submarine threat in time to take appropriate action.
Self-defence capability is largely dependent upon the hostile submarine's firing range which, for a surface combatant conducting evasive steering techniques and employing a range of other ASW countermeasures, is around 4 - 8 nautical miles (NM) which is well within the maximum range of most modern torpedoes. It is also based on the ship itself and effective systems are designed to provide defensive zones around the ship which are often displayed graphically as concentric rings extending outwards from the ship.
Therefore, provided the ship has the ability to search at ranges in excess of 8 - 10 NM it can be said to possess the first part of a self-defence capability. The second half comes in the form of torpedo defence, as it is simply impossible to guarantee that all threat submarines can be detected before they are able to engage. The most common ASW systems deployed for self-defence include the hull-mounted sonar (HMS) and the towed array-based torpedo defence system (TDS).
Force protection capability is based on the ability to contribute to the total ASW surveillance needed by a deployed task group to enable it to remain safe against the prevailing submarine threat. In that context the surface combatant capability should not be viewed in isolation but rather as a contribution to that of the force as a whole. However, it is potentially a most significant contribution given that the surface combatant has to operate continually in the face of a direct threat. Therefore, current surface combatants with an ASW system very much configured for self-defence represent a major capability within the ADF ASW force structure.
It is not easy to define a range to which ASW surveillance should extend, as it is highly dependent upon varying conditions. These include, but are not limited to, the mission, the capability of the adversary and the effectiveness of the overall ADF ASW system, into which the AWD and its attendant sensor and weapon systems fits. However, as a guide the area from approximately 20 to 50 NM is indicative and assuming it is plausible it acts as a good reference for setting effectiveness and then for acquiring appropriate capabilities and, ultimately, systems. Within that range, which nominally extends from the doctrinally accepted definitions of "mid" and "deep" fields, the combination of platform and ASW sensor and weapon characteristics dictates "system effectiveness".
Once, again, as a rough guide the aim should be to maximise the range at which submarines can be countered by creating "layers of defence" and "defence in depth". Broadly speaking the layers extend outwards from the protected force and, consequently, platform characteristics such as mobility influence effectiveness. Defence in depth on the other hand is created through system capability within a layer and the combined effectiveness of the systems within the layer influences the effectiveness. It is this concept which drives doctrine and underpins the employment of ASW assets. It can be seen through the employment of air assets at long range, ships closer to the force and the employment of a range of sensors and capabilities within the layer (or zone) allocated to the platforms.
During its service life the AWD could be required to conduct ASW across a wide range of environments ranging from littoral operations in shallow, warm water conditions with very high levels of background noise to open ocean ASW conditions of deep water and well-defined background noise conditions. This means that the UWW sensor suite and associated combat system, including decision aids, planning tools and performance prediction and monitoring systems need to account for the possibility of operation in every type of environmental condition. Therefore, flexibility of design to cope with this is more important than tailoring for one particular set of conditions.
The most obvious design implication that can be drawn from this is the need for the sensor suite to be capable of operation at the most advantageous depth in the water column, whatever that may be for the prevailing conditions. The system also needs to cope with conditions of varying background noise which in turn leads to sensor design features such as variable source level for active transmitters and techniques for reverberation management. Moreover the sensor suite needs to encompass advanced system management features that allow sensors to be operated in optimal modes for the conditions and the HMI needs to be configured with intuitive displays which allow environmental features to be shown in addition to possible underwater contacts.
To meet the AWD requirement a systems approach should be taken which aims to provide the ship with the right systems to be an effective participant in force protection while still providing high levels of self defence and also capitalising on the ship's considerable Command and Control potential. The ASW capability should also take into account the embarked helicopter(s) which can augment surveillance capability in conjunction with other ADF ASW aircraft and also provide the means by which submarines detected by the ship's surveillance sensors can be localised and attacked with relative impunity.
This process is known doctrinally as "cueing" and is fundamental to surface combatant ASW. Indeed, helicopter employment without decent cueing is problematic at best and potentially inefficient at worst. Cueing has become the measure by which long-range surveillance systems are designed.
In addition to possessing the right sensor suite the AWD must also have the right ASW weapons. Similar to self-defence capabilities currently entering service, the ADF also has the right weapon. The MU-90 Impact lightweight torpedo will be the most effective ASW weapon not only when the AWD enters service but also throughout its operational life.
>From the discussion above the likely UWW systems needed to support the AWD requirement can be deduced. They are an active Variable Depth Sonar (VDS) for tactical surveillance; a Torpedo Defence System (TDS) which draws from both towed array and hull mounted sonar; a Hull Mounted Sonar (HMS) for close-in protection; and helicopter-based acoustic systems (ideally a dipping sonar and sonobuoys). There is also an implicit need for an extensive range of sonar management aids. The rationale underpinning this suite is as follows.
The VDS provides the primary sensor for long range tactical surveillance. Ideally it would operate actively at relatively low frequency and also provide passive coverage for both narrow and broad band surveillance. This mode is more likely to be used in operations other than ASW as the conventional submarine threat is not particularly susceptible to passive sonar. Nevertheless, long range passive surveillance could augment torpedo defence systems.
The HMS as a sensor has come in for considerable, if not uninformed, criticism in recent years but its usefulness is beyond doubt. In the self-defence scenario the HMS provides the means to detect and prosecute submarines as they conduct their engagement and also provides forward hemisphere coverage for the TDS.
The TDS itself is a fundamental requirement as it is the means by which torpedoes are detected and evaluated to enable the correct countermeasures to be applied. The TDS must provide all-round coverage and be capable of detecting the full range of threat weapons the AWD might be likely to encounter in the course of its operations.
In conclusion, the AWD will have a significant ASW role. It will become the primary means by which the surface combatant force contributes to ADF ASW Force Protection. In order to do so it must have the right suite of sensors and must possess the wherewithal to employ them correctly.
Jim Manson is Manager of Defence Strategy for Thales Underwater Systems
By Jim Manson, Sydney