Under a major joint program launched by Belgium and the Netherlands, work on the construction of 12 new mine countermeasures vessels is scheduled to begin in mid-2021. The ships will be equipped with ten robotic MCM payloads, or ‘toolboxes’, comprising around 100 drones. The shipbuilding will take place at yards in Brittany, France, and other work in Belgium and the Netherlands. The contract, awarded on 22 May and worth €2 billion, was won by Belgium Naval & Robotics, a consortium set up by Naval Group and ECA Group. The first vessels are slated to begin replacing Belgian and Dutch Tripartite‑type minehunters from 2024. Belgium is acting as the program prime contractor, the Netherlands playing the corresponding role for the countries’ joint frigate renewal program. The first Tripartite minehunters entered service with the French, Belgian and Netherlands Navies under a tri‑nation program in the 1980s.

Belgian Tripartite-type minehunter Crocus (© Bernard Prezelin)

Mer et Marine has been given access to detailed descriptions of the new ships and their robotic MCM systems to detect, classify and neutralise mines. This article focuses on these Naval Group‑designed vessels and the new page they will open in the history of European mine warfare using airborne, surface and underwater drones.

81m for 2730t

The vessels, serving as motherships for the different drones, are designed for faster, safer MCM operations while dramatically reducing crew exposure to danger. They are also very different from their predecessors. Whereas the Tripartite minehunters have a length overall (LOA) of 51.5m for a beam of 89m and a full‑load displacement of 615t, their replacements will have an LOA of 81.4m for a 17m beam (15.5m at the waterline) and an as‑built displacement of 2730t with provision for increases to an end-of-life displacement of 2800t.

Computer image of a next-generation MCM vessel for the Belgian and Netherlands Navies (© Naval Group)

Low-signature steel hulls

Unlike the Tripartite type, which featured hulls made of a non‑magnetic glass‑reinforced composite material, the new vessels will have all‑steel hulls. “One of the main benefits of the stand‑off MCM concept is that the motherships send their drones into the mine field, instead of going in themselves. This enabled the design team to specify larger vessels with steel hulls and conventional superstructures instead of composites and weight‑saving aluminium respectively,” says Eric Perrot, Naval Group’s MCM program manager. Given that mine fields are not signposted, a mothership may, in practice, find itself in dangerous waters. “In mine warfare, there is always the possibility that a mine or two will go undetected, thereby exposing MCM vessels and their crews to the risk of an underwater explosion.” It is for this reason that the hulls will be made of thick high‑yield steel, the compartment architecture optimised for survivability, and key items of equipment mounted on shock‑proof pads. Together, these choices will ensure optimal protection in the event of a nearby explosion and enable the vessels to pursue their mission or at least survive in the event of a closer explosion. Among other solutions to reduce underwater radiated noise, the ships will also be equipped with degaussing systems and anti‑vibration/shock mounts. The generation and modification of electric fields by the ships will also be attenuated using impressed current solutions and by actively earthing the propeller shafts while the propellers will feature a special coating to reduce the impact of the vessel’s electric fields. Each ship will also be equipped with a mine avoidance sonar, or MOAS, to detect mines on its path during transits.

Turning to explosion survivability, the K factor quantifies the ship’s ability to withstand the detonation of a given mass of explosive at a given distance, Belgium has stipulated values for two coefficients, but further details are, for obvious reasons, confidential. Broadly, the first quantifies the vessel’s capacity to pursue its mission while the second quantifies its ability to remain afloat and sufficiently upright following a powerful nearby explosion to allow the crew to be safely evacuated. These critical design requirements “are broadly comparable to those for a state‑of‑the‑art frigate or similar combatant”.

Propulsion system

The ship’s twin propeller shafts will be powered by a pair of electric motors, each rated at 1750kW, powered by three diesel‑alternator sets, one rated at 2520kW, the other two at 1260kW. “This configuration improves the match between a vessel’s power needs and its generating capacity. The large diesel‑alternator set will be in one compartment and the other two in another. Each compartment will also house one electric motor. To meet the required redundancy in the event of a failure or flooding, one propeller shaft will have to be longer than the other,” adds Eric. The system is designed to offer a cruising speed of 15 knots in sea state 4 at 85% of the three diesels’ continuous combined power rating. This results in a range of 3500nm at 15kts.

Surveillance and self‑defence systems

The surveillance and self‑defence systems will include 12.7mm remote‑controlled machine guns and a 25 to 40mm main gun that has yet to be selected. The sensor suite will include a 2D radar optimised to track MCM UAVs, and electro‑optical radar and fire control systems interfaced with the guns.

Quarters for 63 and dedicated areas for commanders and divers

The shipboard quarters will accommodate 63 with different ranks in individual, twin and four‑bunk cabins. The crew format will be tailored to each mission. Space will be provided for a small command team, with a mission planning area next to the ops room. Given, despite the MCM capabilities of drones and robotics, that some situations will call for human mine clearance, space will be provided for a small team of divers. For their operations, two 7‑metre RIBs will be stored in and deployable from side bays. Space will also be provided for the divers’ gear — from diving bottles, gas tanks, compressors and recyclers to calcium carbonate cartridges. The aft deck can accommodate up to thee 20‑foot containers, including, depending on the mission configuration, one containing a decompression chamber. The others can be used for other equipment or additional drones.

An Inspector 125 USV inspecting a mine (© ECA Group)

MCM toolbox

An ‘MCM toolbox’ — a concept developed by ECA and a core component of the mine warfare program being developed for the Belgian and Netherlands Navies — comprises drones and equipment for a given MCM mission. ECA MCM toolboxes can be deployed on ships, at coastal stations covering ports and harbours, or as containerised air‑transportable modules.

Keeping crew members out of harm’s way

The overriding aim of robotic mine warfare is to keep crew members out of harm’s way and limit dangerous operations to the absolute minimum. The second aim is to clear mine fields as quickly as possible. While the operations from mine detection to clearance remain unchanged, most will henceforth be performed by multiple drones working in parallel rather than sequentially as they are today.

Dedicated drones for mine detection, identification and clearance

Each vessel will deploy one or two Inspector 125 unmanned surface vehicles. Each USV will, in turn, be able to deploy a T18‑M towed sonar, an A18‑M autonomous underwater vehicle (AUV), or a number of smaller SeaScan remotely operated vehicles and K‑Ster C expendable mine disposal vehicles, another type of ROV. The A18‑M AUV can also deploy a T18‑M towed sonar.

The A18‑M AUV and its towed sonar perform mine surveillance and detection to a depth of 300m. The SeaScan ROVs specialise in mine detection using a re-acquisition sonar to re-locate the target mine and cameras, remotely controlled by operators on the mothership, to identify the type. SeaScan ROVs normally approach mines in automatic mode before switching to the operator-controlled mode with data passing over the cable linking the ROV to its USV. The USV is equipped with a radio relay linking it and its mothership.

SeaScan ROV (© ECA Group)

K‑Ster C expendable ROVs are designed specifically for mine clearance. Each is linked to its USV by a thin cable. Given that each K‑Ster C has its own battery pack, the cable does not include a power wire. This is important because a thin cable means less drag which in turn means that the current has less effect on the ROV. “This is critical in the presence of strong currents and where the ROV is deployed several hundred metres from the USV. With a thicker cable, a mine disposal ROV may have to run its thrusters at full power resulting in more magnetic and acoustic noise and in extreme cases it may become uncontrollable. The decision to make the ROVs self powered is essential to the overall concept. This solution is not only more economical, but also superior in operational terms given that power cables are both more expensive and a drain on USV power, thereby limiting its operational capabilities,” says Daniel Scourzic, ECA Group’s marketing manager for unmanned maritime integrated systems, or UMIS.

K-Ster ROV (© ECA Group)

ECA’s K‑Ster C expendable ROVs can be deployed to a range of 1000m and a depth of 600m. The Group has sold the type to Canada, India, Kazakhstan, Lithuania and Singapore. The warhead comprises a shaped charge filled with an insensitive explosive that detonates on contact with the target mine or in its immediate proximity. The tiltable warhead ensures that the charge is accurately positioned relative to the target. “While remaining horizontal, the K‑Ster C tilts its head over a range of ±90° for maximum effect depending on the mine type. For instance, on encountering a partially buried mine, the ROV hovers over it then tilts the warhead to −90°.” In the case of a moored or tethered mine, the K‑Ster C positions itself immediately below or alongside the target.

K-Ster ROV (© ECA Group)

USVs at the heart of it all

The Inspector 125 unmanned surface vehicle is the latest in a long line of MCM USVs developed by ECA. This model has been sold to the Kazakh Naval Forces for operations in the Caspian Sea. The Inspector 125 is 12.3m long by 4.2m in width and features an unsinkable composite hull designed by naval architecture firm Bureau Mauric, an ECA subsidiary. The hull is based on the proven design developed for the V2 NG rescue craft operated by French lifeboat association SNSM.

V2 NG-type rescue craft (© DR)

The design includes a gyroscopic anti-roll system to stabilise the platform at low speeds and when stationary. This enables the USV to launch and recover SeaScan ROVs up to sea state 4.

The Inspector 125 is powered by two 420-hp diesels driving waterjets for improved manoeuvrability. The design offers a top speed of 25kts and, depending on the payload, an endurance of up to 30 hours while operating within 12nm of the mothership or farther using an unmanned aerial vehicle as a radio relay. “Given that the Inspector 125 is required to operate in mine fields, the design team paid special attention to reducing its magnetic and acoustic signatures. It is for this reason that the team opted for a composite hull and anti‑vibration/shock mounts, among other features,” adds Daniel Scourzic.

The Inspector 125 is equipped with a mine avoidance sonar, or MOAS. The modular deck and 3‑tonne payload mean that the craft can be configured for a range of missions. For MCM missions, it can carry up to two SeaScan ROVs on aft launch and recovery devices and six K‑Ster C ROVs in canisters on inclined ramps mounted athwartships.

An Inspector 125 USV with two SeaScan and six K-Ster ROVs (© ECA Group)

An Inspector 125 USV with one SeaScan and three K-Ster ROVs (© ECA Group)

AUVs with towed sonars

Another configuration enables the Inspector 125 to deploy an A18‑M AUV weighing 370kg for a length of 3.8m and a diameter of 460mm. A variant, the A18‑TD, is in service with the French armed forces. The A18‑M’s synthetic aperture sonar can scan the water column and seabed from 3 to 300m with a resolution of 3cm. The A18‑M offers a top speed of 6kts and an endurance of 24 hours at 3kts, depending on conditions. To overcome the difficulties of underwater communications, the AUV preprocesses its sensor data then records it in onboard storage ready to be transmitted over a radio link when the AUV surfaces or rendezvous with its USV or the mothership.

An A18-M AUV (© ECA Group)

An Inspector 125 USV launching an A18-M AUV (© ECA Group)

The T18‑M towed sonar deployed by an Inspector 125 can transmit sensor data directly. This sonar, developed by ECA, shares a wide range of components with the A18‑M AUV, including the body, but with different noses. While the T18‑M has diving planes to control underwater operations, but no motor, the battery pack has been retained to power the sensors for up to 20 hours between recharges. Compared with a sonar receiving power from its USV, the ECA solution combines a simpler and lighter tow rig and a much thinner cable comprising just a tensile strand and an optical fibre for data. “A thinner cable means less drag, allowing the USV to tow at a higher speed and the sonar to dive deeper. As a result, the T18‑M offers higher overall performance than its competitors,” adds Daniel Scourzic. Like the A18‑M, the T18‑M can dive to 300m. In shallow water, an Inspector 125 USV can tow the T18‑M at up to 18kts.

An Inspector 125 USV with a T18-M towed sonar (© ECA Group)

The T18‑M and the A18‑M also use the same launch and recovery system, making it easier to reconfigure the host craft. With component commonality approaching 80%, the designs help to reduce production costs.

The T18‑M and the A18‑M are complementary given that they use the same sonar. While the T18‑M combines speed with continuous communications with the mothership via the USV’s radio relay, the A18‑M combines slightly greater autonomy and a swarming capability enabling a number of them to cover a vast area in record time. USVs are also ideal for missions calling for stealth; a case in point being surveys of beach approaches in preparation for a landing operation.

USVs can also tow conventional mine sweeping gear, but this requires more power. While most of the USVs ordered by Belgium will be Inspector 125s, some may be modified for use in this role by fitting a more powerful propulsion system and ducted propellers.

MCM toolboxes

The motherships are sized to accommodate up to two Inspector 125 USVs, two T18‑M towed sonars, three A18‑M AUVs, three SeaScan ROVs, 40 K‑Ster C expendable mine disposal vehicles, a mine sweeping module, two Remus AUVs, and two Skeldar V200 unmanned aerial vehicles, or UAVs. Each payload, known as an MCM toolbox, will be tailored to the planned operations and deployments. For the moment, Belgium and the Netherlands plan to acquire 100 or more drones with Inspectors, T18‑Ms and A18‑M making up half the total. “A mothership deployed on a mission lasting a few days to territorial waters close to its home port on may only require a few drones. On the other hand, a mothership going to a distant theatre of operations for a much longer time may require a full complement,” says Daniel Scourzic.

A next-generation MCM vessel launching an Inspector 125 USV (© Naval Group)

USV deployment

The overall success of the concept hinges on dependable USV deployment, storage, maintenance and reconfiguration. First, the effects of swells, waves, and host craft motion during USV launch and recovery operations must remain within tight limits even in rough seas. After investigating various concepts, including aft ramps, A-frames and davits, Naval Group opted for pivoting davits on either side of the ‘toolbox garage’. “We have been thinking about drone deployment by MCM vessels and surface combatants for a number of years. The main challenge is pitching, which, unlike roll, cannot be controlled by a stabilisation system. Our studies led us to conclude that the best place for a USV launch and recovery system, or LARS, is slightly aft of midships. Also, the best way to maintain the ship’s heading relative to the swell is to position the LARS close to the quiescent point which, given the hullform, is between midships and one-third aft. We therefore decided to place the LARS systems to the port or starboard of the quiescent point. Subsequent analyses and simulations confirmed that this is the optimal position for USV deployment using a LARS,” says Eric Perrot. “Aside from our own analyses and simulations, this solution is widely used in the offshore oil sector where ships deploy ROVs and the like under particularly tough conditions by launching them over the side,” added Cyril Levy, Naval Group’s head of drone and MCM programs.

Next-generation MCM vessels with Inspector 125 USVs on their davits (© Naval Group)

LARS with floating cradle

Each mothership will have one port LARS and one starboard LARS for its two Inspector 125 USVs. These systems will be located slightly aft of midships and to the port and starboard respectively of the ship’s quiescent point or centre of gravity. Each LARS consists of a pivoting davit with the USV, weighing up to 18t, in a structure comprising a frame and a floating cradle. While a USV is being lowered or raised, it sits in its frame and cradle outside the LARS bay with an outboard cable to a forward arm to stabilise the assembly’s fore-and-aft motion. Some frigates use a similar solution to stabilise their rigid inflatable boats during deployment. Naval Group says that this innovative LARS concept “was developed using a systems approach, the aim being to limit the swinging motion of the USV and frame while the davit pivots and the cable arm, winches and damping system automatically control everything in unison. The synchronised damping and constant tension systems keep all loads and forces within tight limits while controlling the motion of the USV and frame”.

Additional views of next-generation MCM vessels with Inspector 125 USV on their davits (© Naval Group)

When not in use, the LARS is stowed in the garage bay. “The Inspector 125 USVs are quite large. Once a USV is stowed, it is firmly secured and unable to move. While the frame and cradle remain in place, they present no obstruction to USV reconfiguration or maintenance. This is significant as these tasks must be kept as simple and safe as possible to avoid putting either crew members or the mission in jeopardy.” Given that each task presents a risk, damage to a USV is best avoided by strictly limiting the number of tasks to be performed. With further regard to optimal reliability, Naval Group opted for identical, symmetrical and independent LARS systems so a mission can be pursued should one fail. The LARS bays are part of the large garage accommodating the ship’s entire mission toolbox, including all its drones except for the UAVs. “When the curtains are closed, the crew can work on USV reconfiguration or maintenance while sheltered from the weather.”

Passive stabilisation for low-speed operations

USV launch and recovery operations are executed at ship speeds between 0 and 5kts, which is too slow for the fin stabilisers to have any effect — hence the decision to include a passive stabilisation system using the hydro-dynamically controlled flow of a liquid within a specially designed tank. While the solution will be broadly similar to a Flume® system, neither the detailed design nor the supplier have been named at this point. “Passive stabilisation has the advantage that it remains effective when the ship is stationary.” Note that Naval Group has, in principle, designed the ship for drone operations up to sea state 5. This capability will be investigated more thoroughly over the coming 24 months through a program of numerical simulation studies and towing tank tests.

Note too that in addition to the LARS systems, the motherships will also be able to launch and recover AUVs and ROVs using the hydraulic crane on the aft deck and different cages for each type of drone.

A Skeldar V200 UAV ready to deploy (© UMS Skeldar)

Skeldar UAVs

The motherships will be equipped to deploy two Skeldar V200 unmanned aerial vehicles developed by UMS Skeldar (formerly Saab) as these were included in the bid submitted by the Belgium Naval & Robotics consortium. This UAV has already been formally selected by both Belgium and the Netherlands for the MCM program. The UAVs will be housed in a shelter and operate from a flight deck, both of which are on the garage roof. Although the architecture does not include a hangar, the flight deck is nevertheless designed for helicopter operations.

Aside from contributing to surveillance missions, the UAVs are also used as radio relays between deployed USVs and the mothership. “Each mothership’s communications suite offers secure, fully redundant, high-speed, real-time data links with its USVs, whether direct or via a UAV.” Direct links have a range of around 20nm while links via a UAV have a far greater range.

A Skeldar V200 UAV in flight (© UMS Skeldar)

High-quality data links are vital to the concept’s overall viability. Operational decisions by shipboard operators are based entirely on sensor data received from the USVs via these links. The data streams include real-time imagery returned by the T18‑M towed sonars and video imagery returned by cameras on the SeaScan ROVs as they approach mines for identification. The mothership transmits drone commands over the same links to trigger operations like the deployment of K‑Ster C ROVs to destroy duly classified threats. The shipboard operators also remotely control the ROVs during final approach phases.

Mission system

All MCM operations will be managed by a mission system developed jointly by Naval Group and ECA since 2016. “Thanks to development work on drone mission systems as part of Airbus’s SDAM program, Naval Group has acquired extensive know-how in interfacing warship combat management systems to higher level systems like the Nato C4I (or command, control, communications, computers & intelligence) system specified by Belgium. We supply the C3 (or command, control & communications) portion, based on our I4drones range, to build the MCM mission overview component. The C3 portion manages mission preparation, maps the mine fields to be explored, assigns systems to tasks and compiles a timeline for each drone while taking into account the relevant environmental data,” says Cyril Levy. The C3 portion also incorporates the MCM Umisoft C2 (or command & control) system developed by ECA. “This handles the detailed mission planning for each drone along with drone programming and control. It also processes incoming sonar data and gathers environmental data, including bathymetry information.”

Once a mission is under way, say mine field inspection, the sensor data gathered by the drones — including imagery recorded by towed sonars or an A18‑M AUV — is transmitted to the C2 system. All sonar thumbnails are processed by threat classification algorithms developed by ECA and tested by navies that already use Umisoft systems. These algorithms deal equally well with bottom mines, tethered mines and improvised explosive devices (or IEDs). “Once a threat has been classified, the data is relayed to the C3 system which handles real-time mission overview. Data concerning classified mines and their locations is fed to the tactical situation which is updated progressively as new data is received. Next comes the time to tell the USV to launch a SeaScan ROV to accurately identify the mine on the basis of imagery relayed via the Umisoft system. If the threat is confirmed, the USV is instructed to launch a K‑Ster C ROV to neutralise it.”

Naval Group is responsible for topside MCM operations, including the overviewing of MCM operations and situation management in the mothership’s vicinity using surface and air surveillance data supplied by the ship’s sensors and other units. Naval Group is also responsible for the interfaces with Nato systems and all aspects of cybersecurity, the solutions having been incorporated into the mission system from the outset to avoid delays during system development. For its part, ECA manages drone planning and control and analyses incoming sensor data using its C2 system.

Made in Brittany

Brittany will draw considerable benefit from the joint MCM program launched by Belgium and the Netherlands. Hull construction will be shared between Kership’s Lanester yard and the Piriou yard, also in Brittany. Lanester is across the river Scorff from Lorient and Kership is a joint subsidiary of Piriou and Naval Group. The ships will be outfitted afloat at Piriou’s Concarneau yard. Naval Group personnel will be sent to Concarneau to oversee system integration, tests and trials and to commission the combat management system.

Shipbuilding work on the first ship is scheduled to begin in the first half of 2021 followed by the floating out of the hull a year later and delivery in the first half of 2024. This first vessel will be for the Belgian Navy. Belgium Naval & Robotics will deliver the motherships at the port of Zeebrugge. In 2020 ECA will open a new plant in Zeebrugge to assemble, integrate and maintain its drones. The second vessel will be commissioned at a later date by the Royal Netherlands Navy. The other ten vessels will be delivered alternately to the Belgian and Royal Netherlands Navies at a rate of one every six months, the last being scheduled for delivery in mid-2030. The 12-month interval between the delivery of the first and second ships will be used to incorporate changes based on feedback from the first-of-class.

Original (in French) by Vincent Groizeleau published online on 11 June 2019

Translated and adapted by Steve Dyson