by Tamir Eshel
The fast evolution of aerial, surface, and underwater drones attracts naval offensive and defensive planners’ attention with its spherical threat potential. Loitering weapons, explosive boats, and miniature submarines pose as much of a multi-dimensional threat as missiles, guns, and torpedoes. The new unmanned menace is small, but but the com,bined effect of its elements can can disable a powerful destroyer as each of a swarm’s drones can hit a specific weak spot, degrading a ship’s defensive capabilities against more potent killers.
Unmanned Systems in the Naval Domain
Unmanned Aerial Systems (UAS)
UAS are becoming a standard tool for maritime surveillance for their long endurance and comprehensive mission payload. While UAS are operated on land, their missions support maritime domain awareness for task forces at sea, extending coverage beyond the range covered from a surface ship. UAS carry large payloads integrating radar, electronic support measures (ESM), and electro-optical (EO) sensors monitoring vast areas of open sea. UAS can operate far from the task force they support, communicating with the ships and operations centre via satellite links and allowing ships to remain silent.
Maritime forces might also operate UAS at sea, which include vertical takeoff and landing platforms (VTOL). These are more restricted in mission endurance and payload capacity but become an extension of the vessel’s sensor mast, and extend situational awareness.
When ships are in port, inland waterways, or littorals, they could encounter small drones or multirotors (e.g. “fancopters”) launched from shore or other vessels. Using commercial off the shelf (COTS) platforms, multirotors are commonly used by terrorists and non-state actors as aerial improvised explosive devices flying autonomously or remotely controlled to attack targets. Being small targets that are often regarded as a nuisance, they pose a significant threat. Petite surveillance drones can obtain close-in images of classified systems, monitor electromagnetic signals, disrupt EO or electronics. These tiny drones prove to be resilient to most types of countermeasures, particularly when flown in small groups or swarms, requiring specific means to defeat them.
Some of these drones cannot be detected by existing air defence systems. With commercial systems becoming rugged, even militarised, they have rapidly evolved at the open-source pace, creating asymmetric adversaries requiring newer, lower cost, and more adaptable defences.
Smaller aerial drones and loitering weapons deployable from submarines to conduct stealthy surveillance and reconnaissance missions, collect target information and extend the submarine’s reach far beyond the distance covered by its sensors.
Autonomous Surface Vessels (ASV)
ASV are becoming common, operated by navies for security, mine countermeasures, anti-submarine, and electronic warfare. Irregular forces also use fast boats loaded with high explosives, rigged with makeshift automation or remote control to attack slow-moving or anchored vessels. Unlike the small drone that requires precision guidance to achieve an effect with a small explosive, a boat loaded with tens – maybe hundreds – of kilogrammes of explosives can cause significant damage anywhere it hits.
Underwater Unmanned Vehicles (UUV)
There is a growing concern for UUVSs for reconnaissance, surveillance, underwater surveying and mapping roles with the potential to conduct kinetic attacks. These stealthy UUVs are extremely hard to detect and track. Autonomously moving underwater and loitering for days, sometimes operating in groups and conducting unexpected attacks upon an operator’s command, they are even harder to defeat.
Like cannons, torpedoes, mines, or missiles, unmanned systems with loitering weapon derivatives are a respected threat in the maritime domain. Drones – particularly small drones – should be a priority target for their part in target acquisition and communication and sensor denial. Smaller drones are expected to be close to the shore and port while surveillance drones are often seen at sea. Engaging these drones often relies on electronic or EO countermeasures to prevent them from success.
Improvised explosive drones and loitering weapons pose a direct and immediate threat reflected by their offensive behaviour. Due to the limited endurance and range, their threats are often in areas where vessels have limited manoeuvrability – docked in port, passing through narrow straits or canals, and during port entrance.
Future vectors of unmanned platform attacks could rely on hybrid systems, either sensors or weapons, comprised of an aerial platform combined with an underwater vehicle launched from boats or aircraft, conducting reconnaissance or attacking targets above and on the surface.
Modern unmanned systems combine autonomy with “a human in the loop” and rely on an array of sensors to conduct their mission. A defender could exploit the electromagnetic, photonic, and acoustic emissions of drones to detect, track, and disrupt the drones’ operation.
Radar is most useful for detecting aerial and surface targets at sea – day or night, and under all weather conditions. However, drones are difficult to detect as they move slower than aircraft or missiles and have a small radar signature (radar cross-section). Effective radar detection requires specific filtering and signal processing to distinguish drones from other slow-moving objects, such as birds or waves. The primary radars on ships are not optimised for such operation as they focus on other tasks – surface search, missile detection, and air defence. Furthermore, the primary radar is not activated in ports, where ships are vulnerable to terror attacks.
Smaller radars optimised to detect low, slow and small (LSS) targets are optimised for C-UAS. In 2019, when US Amphibious Assault Ship USS KEARSARGE deployed to the Arabian Gulf, it relied on an ad-hoc C-UAS solution provided by a Light Marine Air Defense Integrated System (LMADIS) system to defeat an Iranian drone that approached the ship. The system integrates multiple sensors on a single vehicle, providing mobile, expeditionary C-UAS protection for the US Marine Corps. L-MADIS packs four RPS-42 radars from RADA, a SkyView RF detection package and Modi RF jammer from Sierra Nevada, and an EO payload provided by Ascent Vision.
Other electronic sensors operated onboard are Electronic Support Measures (ESM). This passive Radio Frequency (RF) sensor continuously analyses the electromagnetic spectrum over a wide bandwidth, searching for anomalies indicating that a suspicious activity might relate to a hostile activity. Since unmanned systems have a distinct electronic signature, ESM provides the first alert of a threat to the ship. With its ability to determine the signal’s direction arrival, ESM also provides verification, identification, and localisation of targets detected by radar
Operating on the move poses a significant challenge for the radar, especially with LLS targets that are masked by sea clutter. MCTECH developed a system to overcome motion challenges in a unique way. The MC HORIZON points the radar at a specific area where the passive ESM sensor suspects the drones to be. MCTECH delivered this system to the Royal Thai Navy. Controlled from the bridge, the system is able to bounce or defeat hostile drones from anchored or moving ships.
EO systems are often used for surveillance means, target acquisition, and as fire control systems onboard ships. Different types of EO/IR systems are available for naval vessels and ashore include the SPYNEL from HGH and the iSea Family of Maritime Surveillance System and SPEED ER from Controp. Panoramic thermal cameras, using fast rotating cameras, provide 360-degree coverage and detect multiple targets simultaneously, on the surface and in the air. Modern computer vision detects and tracks multiple targets concurrently by differentiating non-combatant objects by their profile and behaviour. A radar or ESM use EO/IR sensors to spot, track, and identify targets of interest. Provided with a high level of stabilisation and accuracy, sensor payloads can spot small flying objects and target them for other weapon systems.
Facing growing underwater challenges, navies turn to acoustic sensors to detect activity. While bow-mounted and towed sonars can detect large objects (submarines, fast and noisy torpedoes, etc.) they cannot handle slow, stationary or small objects like UUVs or mines, particularly on a moving ship. Sonar specialist DSIT Solutions developed the MonkFish torpedo detection and alert sonar (TDAS) for this purpose. Installed as a secondary bow-mounted sonar, MonkFish operates alongside the primary sonar and is designed to detect UUVs, divers, and advanced torpedoes on stationary or moving ships.
Monitoring large coastal areas and port entrances help protect vessels and offshore facilities from all underwater threats. Such monitoring is achieved by a network of active-passive SeaShield sensors that build a virtual anti-submarine barrier, guarding against underwater threats. Linked by fibre-optical cables, the centrally monitored sensors provide automatic detection, tracking, and classification of targets of interest. DSIT offers a standalone solution for offshore platforms and port surveillance – the AquaShield. This diver detection sonar system was demonstrated in 2018 for the US Navy’s STILETTO Maritime Technology Demonstration Program, performing automatic detection, tracking, and classification of UUVs and divers.
Integrating multiple sensors and data feeds is essential for situational awareness and effective responses. Counter-unmanned missions require an integrated approach to establish situational awareness over a 360° perimeter around an asset. NiDAR, from Monaco-based MARSS Group, is such a system. The intention was to initially to secure superyachts. NiDAR employs smart software algorithms to autonomously and intelligently detect, classify, and respond to aerial, surface, and underwater objects to determine potential threat levels and trigger alerts.
Weibel Scientific conducted extensive in-house development resulting in the novel XENTA product family, a new generation of counter-drone and short-range air defence radars. This ground-breaking radar system is designed to detect, track and classify LSS targets, such as UAVs – and conventional air threats like fighters and helicopters. The XENTA family meets the strictest requirements for drone detection and air surveillance – including critical infrastructure and border, perimeter control, and air defence applications. It provides high-performance 3D detection, tracking and classification by combining FMCW and CW digital-array beam forms with advanced dynamic clutter-mapping and MTI-D processing.
These radars increase the distance at which even the smallest micro-Doppler signals can be detected. The radars can track a DJI SPARK micro-drone beyond 2.5 klometres, with micro-Doppler signature classification of the propellers beyond 1.5 klometres. The DJI PHANTOM IV drone can be tracked up to 6 km with classification up to 4.5 km.
Soft and Hard Kill
When an unmanned vehicle is detected and determined as a threat, soft and hard-kill countermeasures are used to repel or destroy it. Electronic jamming is the most common countermeasure. They produce jamming protocols to disrupt the drone’s control channel or deny GPS location to distract its navigation. However, this can cause havoc on a ship, the mission of which and self-defence depends on electronic systems that jammers can disrupt.
When commercial drones are deployed, defenders can hijack the drone by means of a cyber attack, which might not always work against military drones. Nevertheless, solutions such as ECLIPSE from NSO Group allows defenders to take over and safely land an invaiding UAV, allowing the captors to analyse its nature and asses its threat level.
Citadel Defense Company offers TITAN, a C-UAS system for safe use on board ships. The system went through extensive shipboard evaluations and deployments with US Navy destroyers and an aircraft carrier to demonstrate effective onboard operation. TITAN detects drones from a range of about 2.5 miles and delivers an escalated RF countermeasure effect to match the detected threat without interfering with nearby communications. The system employs machine learning and artificial intelligence to identify targets and update its threat library with a new adversary immediately upon detection. According to Citadel, TITAN detects controller, video, telemetry, and Wi-Fi communication links from 400MHz to 6GHz to identify air, land, and sea drone threats. The system has proven success in defeating individual drone threats, and swarm attacks with surgical precision at standoff distances beyond line-of-sight.
Drone swarms are becoming of greater concern due to their “group immunity”. The French Icarus Swarms company and associated CERTIFENCE began to operate drone swarms as a RED TEAM testing C-UAS systems’ resilience to evaluate risks. Such evaluations are conducted through a protocol of 15 tests employed with groups of real drones. Challenging defence systems of different types, CERTIFENCE showed most current systems cannot cope with even small drone groups. Tiny drones cannot destroy a ship, but when targeted at ship sensors, defensive systems, and the close-in weapon system (CIWS) itself, they degrade the vessel’s defensive capability and open the way for a lethal attack by much heavier weapons.
A somewhat more aggressive measure is a physical interception. XTEND’s SKYLORD uses a small UAV interceptor that engages uninvited drones by colliding the drone with an airborne arresting net towed by the interceptor drone. SKYLORD combines augmented reality (AR) guidance and control technology to enable an operator to perform the complex intercept with ease and precision.
Different types of arresting nets are also in use against unmanned platfoms. The STINGRAY UUV interceptor net from Maritime Arresting Technologies is deployed along the target’s course of movement, at the path of a suspected UUV. STINGRAY protects the entire water column, extending from the water surface to the seabed.
Kinetic Hard Kill
Used as part of existing naval defensive measures, guns and lasers can generate effect against drones. But these weapons also need some adaptation. Existing radars associated with CIWS are not geared to track slow targets. Furthermore, destroying a group of drones or loitering weapons a few hundred yards from the vessel may be challenging, mainly when a drone swarm performs coordinated manoeuvres that distract the defender from their main threat.
Such adaptations were recently made to RAFAEL’s TYPHOON MK-30C 30mm naval remote weapon station (NRWS), adapting it to the C-UAS role. Improvements include higher elevation and depression angles for the gun and improved stabilisation of the system’s EO/IR targeting system to enable tracking and engaging these small targets. To engage targets at the maximum range, the NRWS employs active target detection that searches the entire field of view for known target profiles and highlights them for instant evaluation by the shooter. Using programmable airburst ammunition, NRWS has demonstrated neutralising drones at ranges of 2-3 km.
Software upgrades enable real-time computer vision processing for target detection, identification, and tracking. These improvements boost accuracy by introducing an automatic targeting capability that incorporates a diverse mix of synchronised multi-spectral sensors, weapons, and intelligent effectors that result in high hit accuracy. Automatic target recognition, classification, and tracking (ATR), automatic target acquisition (ATA) technologies improve detection, recognition, classification, and tracking of elusive, small targets.
Engaging targets below the waterline also requires special ammunition. A concept developed for the US Navy combines an armour-piercing effect with the ability to shoot straight through the water using the super-cavitation effect. As it pierces through the water, the projectile is engulfed by a low-pressure air bubble, reducing drag drastically. This dual effect means the same ammunition can be fired against surface and submersible targets.
Defence at the Speed
Future C-UAS effectors could further laser weapon developments. Several navies are already testing laser weapons, including those of the US, UK and Germany. Lasers are considered effective against soft targets such as drones and fast boats and operated autonomously or to enhance other defensive systems onboard to defeat simultaneous missile attacks.
The US Navy is moving quickly to include laser weapons to boost the protection of its combat ships. In 2020 the US Navy tested the Laser Weapon System Demonstrator (LWSD) built by Northrop Grumman on the PORTLAND amphibious transport dock (LPD-27) ship. For destroyers and frigates, the Optical Dazzling Interdictor – Navy (ODIN) is developed. The prototype was integrated in 2020 on USS DEWEY (DDG-105), an ARLEIGH BURKE-class guided-missile destroyer. Built by Lockheed Martin, ODIN is less potent than LWSD but achieves an effect at a more extended range since it is designed to distract and blind electro-optical sensors rather than destroy incoming threats.
The German Navy plans to test its laser this year. The first project will use a 20 kW fibre laser made by Rheinmetall, mounted on the class F124 SACHSEN frigate.This laser effector consists of 12 nearly identical 2kW fibre laser modules with close to diffraction-limited beam quality. A beam combiner couples the 12 fibre-laser beams to form a single, weapons-grade laser beam. The modular assembly has growth potential in the 100kW performance class.
But the rush to add C-UAS capabilities on board should not be hasty. Sensors and countermeasures must be carefully tested and integrated with the ship’s systems, and concepts of operation have to be developed to cover the looming threat of small and slow drones while avoiding disruption to the ships’ systems.