Forging tomorrow’s soft-kill shield

Electronic countermeasures (ECM) to defend warships against guided weapon attacks are not a new development. Rudimentary jamming devices were fitted to Royal Navy and US Navy ships as far back as 1943 to disrupt the communications link used in German Hs 293 and Fritz-X radio-controlled bombs. Subsequently, off-board expendable decoys, typified by radio frequency (RF) chaff, have been widely fitted since the 1960s to confuse targeting, distract active radar seekers in the search phase, and seduce seekers in the terminal homing stage.

However, there is a recognition that the anti-surface threat has evolved substantially in recent decades. Anti-ship guided weapon systems have become more diverse, more adaptable and more intelligent in their use of the electromagnetic spectrum to find, fix, track, target and engage. Warning times have been slashed as missiles have become either faster or more stealthy. And adversaries have become more adept in their planning and tactics; for example, combining and coordinating different weapon types to generate complex multi-threat, multi-axis attacks.

Moreover, characterisation of the threat increasingly blurs the boundaries of ‘conventional,’ ‘hybrid’ and ‘asymmetric’. Proliferation of anti-ship cruise missiles and anti-ship ballistic missiles to proxies and non-state actors has become a reality, latterly evidenced by the Houthi attacks on shipping transiting through the Red Sea. Cheap and abundant one-way attack drones may further complicate the threat calculous.

Assuring an acceptable level of maritime platform survivability in the face of this increasingly stressing threat presents new challenges for ship defences. Inherent constraints within a platform – such as the replenishment limitation of hard-kill anti-air missiles and numbers of vertical launch silos – quickly compromise a maritime platform’s ability to function in a contested environment. This situation has forced operational practitioners, the defence scientific community and industry alike, to think afresh about the contribution that soft-kill devices – and specifically off-board countermeasures – can make as part of a balanced ship self-protection suite. In particular, there is an understanding that soft-kill has a vital role in redressing the unfavourable cost exchange advantage currently enjoyed by adversaries, and adding ‘magazine depth’ both to augment and complement hard-kill effectors.

This renewed interest in soft-kill anti-ship missile defence (ASMD) is reflected in a number of identifiable strands of science, research and technology development: the development of advanced countermeasure payloads to overcome increasingly sophisticated counter-countermeasure techniques; the proliferation of a new generation of trainable decoy launcher systems able to place countermeasures payloads with improved accuracy in time and space; moves to field a new generation of persistent countermeasures hosted on long endurance carrier vehicles; and the development of advanced software-driven electronic warfare command and control (EWC2) functionality to plan and coordinate the soft-kill response, and synchronise with other defensive responses.

Payload evolution

Chaff has been the mainstay of soft-kill ASMD over half a century, reflecting the preponderance of RF-guided anti-ship threats deployed worldwide. Effectiveness has been enhanced over time thanks to engineering improvements such as variable range and height of burst, optimised payload placement patterns, and faster bloom time. Infrared (IR) decoys designed to seduce IR threat seekers are also a standard feature of most soft-kill decoy systems. Modern naval IR decoys typically deploy a series of individual payloads/or sub-munitions at variable ranges to ‘walk off’ the seeker of the threat missile. Dual-mode RF/IR seduction countermeasures are designed to present a combined a multispectral response. These rounds – dispensing co-located chaff and IR payloads – address the need to provide signature-matched protection for low-radar cross section (RCS) ships, and offer a capability to counter dual-mode seeker threats.

From a payload perspective, the biggest change in the market is a recognition that the efficacy of chaff is being eroded by the proliferation of missiles using advanced active radar seekers embodying sophisticated electronic counter-countermeasures (ECCM) techniques. There are also threats emerging in portions of the electromagnetic spectrum outside of the conventional chaff bands, most notably millimetric wave (mmW) radar seekers operating in the 35 GHz region (Ka-Band).

Given these concerns, interest has grown in the use of corner reflector payloads as an alternative to chaff. The employment of this technology is by no means new; floating corner reflectors have been used by the British Royal Navy (RN) and a handful of other navies since the 1980s. However, recent years have seen a number of decoy manufacturers package smaller, slow-descent airborne corner reflectors into standard countermeasure cartridges. Advocates of this technology argue that corner reflectors afford several advantages over chaff including: a consistent response irrespective of the threat bearing or azimuth; no need for prior threat knowledge; insensitivity to the polarisation of the RF seeker; a radar return that is more representative of a ship target in terms of scintillation, glint, polarisation, spectral density fluctuations, and range/azimuth error signals; resistance to the chaff discrimination logic employed by modern RF seekers; and multi-band performance extending into the Ka-Band.

One example is the WIZARD countermeasure developed by Israel’s Rafael Advanced Defense Systems. This deploys a broadband payload comprising a pair of fast-inflating corner reflectors.  Lacroix Defense in France has also embraced corner reflectors, albeit taking a different technical approach. Rather than an inflatable decoy, Lacroix’s SEALEM round deploys a pyrotechnically-activated ‘pop-up’ structure that expands instantaneously so as to minimise the time between the firing command and the delivery of a high RCS decoy effect. According to the company, the use of a pop-up mechanism provides for a very stiff and stable structure with a very precise geometry, thus creating a more credible RF return.

Another approach, more complex in its execution and effect, is to deploy an active off-board decoy – a mini-jammer – to achieve angular seduction. This type of countermeasure, which marries an electronic warfare payload from a cartridge or using a carrier vehicle, seeks to ‘capture’ the threat missile seeker and then generate a jamming waveform to pull it off the intended target. Active off-board decoys are, round-for-round, far more expensive than chaff or corner reflectors. However, they bring a number of advantages: only one decoy expended per engagement; no requirement for evasive manoeuvres; and a capability to defeat the most sophisticated ECCM logic.

The best known example of an active off-board decoy is the Mk 234 Nulka round. A joint Australian/US development, Nulka combines a hovering rocket flight vehicle (produced by BAE Systems Australia) with a US-manufactured EW payload.  The original Nulka electronic decoy cartridge mounted a broadband RF repeater payload produced by Lockheed Martin. To counter more advanced threat seekers, a so-called Advanced Decoy Architecture Program (ADAP) has been pursued as a rapid development effort to meet both US Navy and Royal Australian Navy needs. L3Harris is responsible for delivering ADAP payloads – using an advanced transmitter and improved signal processing – to target specific threats outside the performance scope of the existing Nulka payload.

Rafael Advanced Defense Systems has taken a different route with its C-GEM active off-board decoy. Packaged in a 115 mm cartridge, the rocket-powered C-GEM is fired to its intended range/bearing before deploying a Digital Radio Frequency Memory (DRFM) EW payload beneath a parawing. C-GEM has recently entered Israeli Navy service on the new Saar 6 corvettes.

Trainable launch

It goes without saying that any decoy must replicate the signature characteristics of the actual target so as to present a credible alternative to the threat seeker. However, the efficacy of any soft-kill response also depends on the deployment of the decoy(s) to the right position in time and space such that it is located inside the seeker range and angle ‘gates’. Any target – or decoy – outside of this volume will be ignored or rejected. This is particularly important for countermeasures being deployed for distraction (when the seeker is in the search phase) or seduction (when the seeker will have framed its tracking gates around the target).

Many legacy decoy systems have used fixed launchers with barrel sets angled at pre-set bearings and elevations. While fixed launchers are simple, reliable, easy to maintain, and occupy a small deck footprint, they suffer from a number of limitations.

• First, they are inherently constrained in terms of the accuracy of decoy placement because they lack any form of stabilisation or positional capability.
• Second, they demand careful selection of the launcher ‘barrel of choice’.
• Third they cannot fully exploit the performance of more advanced multi-part decoy rounds.
• Fourth, they require the defended ship to perform carefully coordinated manoeuvres as part of the countermeasure ploy.

Accordingly, more and more navies are investing in fully stabilised and trainable decoy launch systems. While these equipments are larger, heavier and more complex than fixed launch systems, their ability to traverse and elevate with precision affords far greater accuracy in the delivery of decoy payloads/patterns, enables the optimised deployment of advanced RF and IR countermeasures programmable in height and range, and minimises/obviates the need for ship manoeuvre.

Elbit Systems in Israel was amongst the first companies to introduce a trainable decoy launcher in the shape of its Deseaver system. Originally designed in the early 1990s to meet the needs of the Israeli Navy, variants of Deseaver are currently fitted to the Israel Navy’s Saar 4.5 strike craft, Saar 5 corvettes and, in the case of the latest Deseaver Mk 4, the new Saar 6 corvettes. All variants in Israeli service are engineered to fire standard 115 mm decoy rockets supplied by Rafael.

Rheinmetall’s Multi-Ammunition Softkill System (MASS) is another example. Conceived in the early 1990s, MASS uses a lightweight trainable launcher to fire 81mm OmniTrap multispectral decoys so as to provide a capability to counter RF, IR and electro-optical seekers.  MASS has established itself as a market leader, with over 240 launchers sold to 16 customers, Each MASS launcher can host up to 32 OmniTrap munitions: the system solution offers ‘five degrees of freedom’ with regard to bearing, range, altitude, number of decoys, and firing interval between decoys.

French company Safran is another exponent of trainable launchers. Its NGDS (New Generation Dagaie System) – developed as the successor to the widely sold Dagaie and Dagaie Mk 2 decoy systems – uses a twin-axis launcher trainable in elevation and azimuth to enable accurate decoy placement to counter specific threat types. To meet the specific needs of the French Navy, countermeasures supplier Lacroix Defense developed a new generation of NGDS-compatible SEALEM and SEALIR 150 mm decoy rockets (respectively deploying advanced RF and IR payloads). NGDS has been installed on the French Navy’s ‘Horizon’ anti-air warfare frigates and Aquitaine class multi-mission frigates. It has been exported to the navies of Morocco, Egypt and Singapore.

The major change impacting the trainable decoy launcher market in recent years is the introduction of systems compatible with NATO standard 130mm rounds. Prior to this, users of 130 mm decoy cartridges were restricted to using fixed barrel launchers such as the US Navy’s Mk 137 (part of the Mk 36 Decoy Launch System). Both Safran (NGDS Configuration D) and Elbit (Deseaver Mk 4) have now introduced variants of their existing launchers adapted for 130 mm decoys.

Meanwhile, United Kingdom company SEA has introduced a brand new 12-round launcher system, known as Ancilia, to the market. Procured to meet the RN’s Electronic Warfare Countermeasures Increment 1a requirement, the Ancilia system combines a trainable launcher (using twin six-barrel ‘cassettes’ mounted on a training/elevating platform developed by Chess Dynamics) with inboard launch control electronics developed by SEA as part of a technology refresh for the RN’s legacy Outfit DLH fixed launcher. SEA has recently teamed with Denmark’s Terma to integrate Ancilia as part of an improved Mk II variant of Terma’s widely sold C-Guard 130 mm soft-kill countermeasures system.

Persistent effects

As the ASMD threat evolves – with warning times reduced and an increased threat from multi-axis salvo attacks – navies are becoming acutely aware of two major drawbacks associated with ‘traditional’ shipborne decoy systems. One is that they are reactive in operation, which means that there is an inevitable delay between receipt of warning, system initiation and payload deployment/effect. The other is that expendable decoys have a short duration of effect; from several tens of seconds to a few minutes.

In response to this changing threat dynamic, several naval forces have funded science, technology and experimentation activity to explore the technical feasibility and operational practicality of persistent off-board soft-kill marrying an EW payload with a long-endurance carrier vehicle. While one solution is to use a crewed helicopter as the host for an active ECM payload, the greatest potential over the longer term is by means of autonomous uncrewed systems either flying or sailing in consort with a ship or task group.

The US Naval Research Laboratory (NRL), under the sponsorship of the Office of Naval Research (ONR), has been pursuing technology demonstration for several years. One example is the Netted Off-board Miniature Active Decoy (NOMAD) low-cost rotary-wing mini-UAV developed by the NRL as a part of ONR’s NEMESIS (Netted Emulation of Multi-Element Signatures Against Integrated Sensors) Innovative Naval Prototype programme. Capable of deployment as either as a single unit, or in a coordinated ‘nest’ of multiple decoys, the ‘soft-launch’ NOMAD vehicle is effected from a tube launcher and then deploys flip-out counter-rotating coaxial rotors located at either end of a longitudinally-extending body.

US Navy ambitions in this area are currently being taken forward under the Long Endurance Electronic Decoy (LEED) programme, which is itself drawing on technologies developed and matured under the ONR’s Long Endurance Airborne Platform project. Integrating with the shipboard AN/SLQ-32(V)6 and V(7) systems, LEED is intended to provide the fleet with enhanced EW coordination and capability, including the ability to stretch engagement timelines and counter heterogeneous missile attacks. Lockheed Martin is prime contractor for the LEED development effort. Production representative units are planned to complete at-sea capability assessments towards the end of the decade.

Unmanned surface vehicles (USVs) are also being evaluated as potential EW payload carriers. Canada’s Naval Electronic Attack Recapitalization-Unmanned (NEAR-U) project, being led by Rheinmetall Canada, has pursued the implementation and test of a Naval Off-Board anti-Missile Active Decoy that integrated an Elbit DRFM-based EW payload with a QinetiQ Humpback USV. The latter is a variant of QinetiQ’s existing Hammerhead unmanned surface target vehicle modified for specific payload applications. Meanwhile, Rafael Advanced Defense Systems has advertised development of a dedicated EW variant of its Protector USV system able to contribute to both ASMD and area defence. The payload for this solution would exploit technology from the company’s C-Pearl-DV digital electronic support measures and Digital Shark EA systems to create a lightweight, compact EW module suitable for unmanned operation.

Electronic warfare command and control

The final piece of the soft-kill jigsaw – and arguably the most important – is electronic warfare command and control (EWC2). EWC2 encompasses the planning, management and employment of EW resources – including de-conflicting or synergising hard-kill and soft-kill responses – to maximise ship or force survivability. Historically a so-called ‘mandraulic’ activity reliant on well-drilled responses from EW operators and the wider command team, the pace of the modern warfare environment increasingly demands that EWC2 is automated, with tactics and doctrine encoded in software to improve response time, alleviate operator cognitive load, and optimise the use of resources.

At the single ship level, EWC2 can function in a manner akin to the threat evaluation and weapon allocation (TEWA) functionality resident in hard-kill systems. This TEWA process will then drive a recommended decoy firing solution/countermeasure type based on the multiple variables pertaining to a specific threat scenario (including, but are not limited to, threat angle of approach, threat speed, threat seeker parameters/characteristics, own ship course and speed, and wind speed and direction). Force level EWC2 looks at the survivability of the broader task group, recognising that not all units will be fitted with decoys or even sensors. This may require a ship to deploy a decoy to protect a ship in consort.

One example of EWC2 is the Soft Kill Coordination System (SKCS) being introduced to US Navy DDG-51 guided missile destroy

ers as part of the SEWIP Block 2 upgrade. Designed to improve decoy effector coordination and enhanced situational awareness in support of soft-kill engagement decisions, the SKCS is an ‘in-house’ navy development involving the Naval Surface Warfare Center Dahlgren Division and Johns Hopkins University Applied Physics Laboratory.

Meanwhile, an EWC2 function is a key part of the Maritime Electronic Warfare Systems Integrated Capability (MEWSIC) Increment 1 system being delivered to the RN by a team of Babcock International and Elbit Systems UK. The ship-level EWC2 functionality in MEWSIC Increment 1 will automate EW engagement planning with users ‘on the loop’, embed tactics for multi-threat engagements, and include the ability to take indicators and warnings from any organic or non-organic source. Its open architecture has been designed to accommodate expansion through-life, including future force-level EWC2.

Author: Richard Scott is a UK-based analyst and commentator who has specialised in coverage of naval operations and technology for over 25 years, with particular interests in the fields of naval aviation, guided weapons, electronic warfare and autonomous systems.