Focus on France’s next-generation SSNs

Focus on France’s next-generation SSNs

“There are no silver medals in this game. When facing the enemy, the only option is to be the best and to win,” said Admiral Christophe Prazuck, French Navy chief of staff, at a press conference in Cherbourg on 12 July. He was responding to a question on the merits of France’s next-generation Barracuda-type nuclear-powered attack submarines (aka SSNs), compared to the highest performance SSNs deployed by other navies. Admiral Prazuck, who served in the submarine force in the 1980s, then on ASW frigates in the 1990s, stands by his unequivocal reply. The Suffren*, the first of France’s Barracuda-type SSNs, was unveiled in Cherbourg on 12 July and floated off the floor of a floodable dock three weeks later on 2 August. Six Suffren-class boats are scheduled to join the fleet between now and 2029. Together, they will give the Navy a top-class SSN fleet for many years to come. “When we asked the defence procurement agency (DGA) for the type of boat we need for our missions, we obviously asked for the best. In fact, we asked not only for the best, but for the best over the next 40 years.”

 

Admiral Prazuck with Admiral Rogel and General Lecointre at Cherbourg on 12 July (© Mer et Marine – VG)

 

 

Suffren unveiling, Cherbourg, 12 July (© Mer et Marine – Vincent Groizeleau)

Suffren unveiling, Cherbourg, 12 July (© Mer et Marine – Vincent Groizeleau)

 

Constant progress

Although the Barracuda program was set in motion back in 1998 and the contractors were awarded formal contracts in 2006, it has been and remains open to ongoing technological innovation. The design process, like those adopted for other long-term military programs, uses a modular architecture that is open to change. The process used for current-generation French submarines has consistently anticipated new developments and accommodated innovations over the years. And it will be no different for the Suffren class. Studies and analyses already in hand are examining future advances in various areas. “Given that the commander of the last of the Suffren class has not yet been born and that his parents have probably not even met, it’s clear that we have to think a long way ahead. All the way out, in fact, to 2060,” says Admiral Prazuck with a smile. The Barracuda’s larger hull offers more space to upgrade existing equipment and add new capabilities throughout each boat’s lifespan in response to the continuing move to all-digital systems and the accelerating pace of technological change across the board.

 

SSN Suffren on hydraulic ‘walkers’ ready to proceed to the DME dock and shiplift after leaving the Laubeuf assembly hall (© Reuters)

 

“A major industrial and technological achievement”

The design, construction and regular upgrading of this type of vessel calls for a “long-term view,” said President Emmanuel Macron at the Suffren unveiling at Naval Group’s Cherbourg shipyard. President Macron is the fifth French president since the Barracuda program first got under way. President François Mitterrand took the first round of decisions in 1998; the first industrial contracts were awarded under President Jacques Chirac in 2006; and construction proceeded under Presidents Nicolas Sarkozy and François Hollande. “These submarines are a major industrial and technological achievement,” said President Macron addressing employees of Naval Group’s Cherbourg yard, program partners and distinguished guests. Nuclear-powered submarines are, far and away, the most complex machines ever built by human kind. They are far more complex, for instance, than fighter aircraft, spacecraft launchers or the most sophisticated vehicles. And they are more than just a feat of engineering, as President Macron pointed out: “You’re building more than submarines here. What you are building is the independence of France, our sovereignty, our freedom of action, our very status as a great power.” He went on to say that “only four countries can build vessels like these without outside assistance,” namely the United States, Russia, France and China. While the United Kingdom has both SSNs and SSBNs, the ballistic missiles they carry and some key reactor technologies are supplied by the USA. New entrants to the game include India, which is developing its first nuclear-powered boats, and Brazil, which has plans to launch an SSN program in the coming years.

A global boom in submarine construction

The Suffren unveiling was held at a time when the threat posed by submarines all over the world is growing. The Russian fleet is now the same size as it was during the Cold War and operating not only in the Atlantic, but also, and increasingly, in the Mediterranean. This means that western navies, beginning with France’s, must be more vigilant. The Chinese fleet is also expanding and regularly sending its boats to the Indian Ocean, with the prospect that they will advance farther west to waters where its surface vessels already operate regularly, and even as far as the approaches to Europe. The challenge is indeed global given that both the number of submarines at sea and the number of countries deploying them continue to grow steadily. Of the 450 or more subs in service around the world, around 70 are coastal types or mini-subs, 250 are diesel-electric blue-water types and 130 are nuclear powered.

The current boom in submarine construction – with work in progress worldwide on around 100 – is due to the fact that they are seen as strategic assets for the defence of a country's maritime interests. In the last five years alone, the number of subs in service has increased by 6%. Today, one navy in five uses them and the numbers are growing, the Vietnam People’s Navy being one of the latest to join the club. New-generation diesel-electric subs, or SSKs, also use new technologies ensuring higher performance. Air-independent propulsion, or AIP, enables these boats to stay submerged for longer, thereby significantly reducing the impact of their major weakness: the need to surface at regular intervals, or at least come up to snorkel depth, so that their diesel engines can recharge the batteries they use when submerged. Surfacing is when SSKs are at their most vulnerable.

 

Computer graphic, Barracuda on patrol (© Naval Group)

 

The only place still left to hide

Submarines derive their appeal from the fact that deep water is the last space where a vessel can manoeuvre while escaping surveillance from the air or space. Given that the laws of physics limit the detection capabilities of assets on and above the sea’s surface, this is expected to remain the case for a long time to come.

The freedom to manoeuvre underwater, to discreetly monitor the adversary’s activities and to have the advantage of surprise are therefore of greater strategic importance than ever. Providing, of course, that the submarines in question offer high performance. Why? Because, while underwater detection, identification and tracking remain complex arts, the sonars deployed by surface vessels and naval aircraft also benefit from constant technological advances. A case in point is France’s new-generation FREMM ASW frigates which submariners describe as a ‘nightmare’ (see also Une chasse au sous-marin sur FREMM). Fortunately, few navies have such assets or the expertise to exploit them to the full, the expertise in question being a combination of equipment design skills, deep crew knowledge and exhaustive training. Here, France’s internationally acclaimed level of excellence – recognised by the US Navy among others – is the direct result of the know-how acquired over almost six decades from the country’s submarine-based nuclear deterrence program. Moreover, the strategy’s credibility hinges on technical and human resources of the highest calibre, hence submarines that are both extremely quiet and equipped with the very best sensors and weapons.

 

A French Navy Le Triomphant-class SSBN on the surface for a photo shot (© French Navy)

 

Generation after generation

France’s Le Triomphant class of nuclear-powered ballistic-missile submarines, or SSBNs, commissioned between 1996 and 2010, represented a technological leap in performance by incorporating break-through innovations relative to the country’s first-generation SSNs and SSBNs. They were significantly quieter than their predecessors thanks to lessons learned through the Redoubtable-class SSBN and Rubis-class SSN programs. Recall that the Suffren class will replace the Rubis class and put French submarines back among the world’s best. Aided by government-backed R&D, French contractors drew on their past experience and the latest advances in all-digital technologies to improve performance in leaps and bounds. The achievements already incorporated into the first of the Suffren class will also serve as a basis for further improvements when work begins on designing France’s third-generation (SNLE3G) SSBNs. With the construction of the first expected to begin at Cherbourg in two or three years’ time, this class should begin to replace the Le Triomphant class by 2030. Where possible, innovations adopted for the SNLE3G type will be incorporated into the Suffren class as part of standard upgrades, given that improvements made to one generation are transferred to the previous generation as soon as practicable. “The advances separating the Rubis and Suffren generations represent a subtle balance between lessons learned, know-how acquired and the latest advances. We’ve built on earlier developments, existing know-how and our ability to integrate current and future advances without compromising our rigorous standards with regard to nuclear and dive safety,” said the DGA’s Barracuda program manager.

 

Computer graphic, Barracuda on the surface (© Naval Group)

 

Main missions

The Suffren class will have three main missions. First, protection of SSBNs on nuclear deterrent force (FOST) patrols. In this role, they will work with frigates, helicopters, maritime patrol aircraft and minehunters to safeguard SSBNs setting out or returning from ocean patrols, which is to say when they are not yet or no longer ‘diluted’ in the ocean and can therefore be detected and tracked by an enemy sub in the vicinity. Second, the new class is designed for intelligence gathering, to deploy special forces, and to escort carrier and amphibious groups. The third mission is one assigned to all SSNs, namely anti-ship and anti-submarine warfare. “With the Suffren, a new fighter is born, a combat-capable submarine that will meet the adversary and, often enough, monitor it unnoticed. It will be used to ‘sanitise’ areas SSBNs pass through to ensure that no adversaries are present. It will protect the Charles de Gaulle carrier group, at times from several hundred kilometres ahead. Using its listening and observation capabilities, it will gather intelligence to understand what is happening at sea and on land. Finally, it will act like a sniper capable of hitting targets hundreds of kilometres away with its missiles, or a delivery platform for special forces on offensive or intelligence missions," says Admiral Prazuck.

Bigger than the Rubis class, but still compact

The Suffren and its sisterships – the Duguay-Trouin, Tourville, De Grasse, Rubis and Casabianca – will replace the Rubis class, the world’s smallest SSNs, which entered service between 1983 and 1993. These boats are 73.6 metres in length for a diameter of 6.4m and a submerged displacement of around 2670 tonnes. They carry a crew of 68, plus two ‘golden ear’ sonar operators, a payload comprising up to 14 heavyweight F17Mod2 torpedoes and Exocet SM39 anti-ship missiles, and can also lay mines.

While much smaller than the Le Triomphant-class SSBNs (138m in length by 12.5m in diameter for a submerged displacement of 14,300t), the Suffren class (99m in length by 8.8m in diameter for a submerged displacement starting at 5200t) is far bigger than its predecessors. They are, nevertheless, comments an engineer, “extremely compact”, especially compared with the US Navy’s Virginia class (115m, 7800t), the Royal Navy’s Astute class (97m, 7400t), or the Russian Navy’s Akula II class (114m, 9650t).

Barracuda cut-away view (© Naval Group)

 

Better endurance, quieter too

The bigger hull offers greater endurance given that an SSN’s patrol time is limited chiefly by the stores it can carry. The Suffren class will have an endurance of 70 days at sea, compared with 45 for the Rubis class and around 90 for the Le Triomphant class. A bigger hull also contributes to improved stealth, hence improved ‘invulnerability’. To prevent any vibration or radiated sound from reaching the hull, all less quiet items will be on anti-shock mounts and suspended cradles; a technology carried over from the Le Triomphant class. Note, however, that unlike other types of SSNs, the outer hull of the Suffren class will not be fitted with anechoic tiles. This technology is apparently under investigation for the SNLE3G SSBNs and, if adopted, may later be retrofitted to the Suffren class. The inside of the hull is, on the other hand, lined with anechoic materials, primarily cork.

 

Nuclear powerplant, last pipework connections and checks (© Technicatome / CEA)

 

Nuclear propulsion

A submarine’s propulsion system holds the key to its stealth. The Suffren is equipped with a pressurised water reactor (PWR) based on the K15 family powering Le Triomphant-class SSBNs and the Charles de Gaulle aircraft carrier. “Nuclear propulsion offers many advantages, including no at-sea waste or exhaust gases, a small number of rotating machines, hence improved acoustic discretion, and, of course, tremendous endurance and range. The extremely demanding nuclear safety requirements for military applications – which go even further for the Suffren class than for earlier types – can only be met by complying with the very highest quality standards across the board,” says Loïc Rocard, CEO of reactor manufacturer Technicatome. The reactor fuel’s high energy density enables nuclear-powered vessels to carry a huge amount of energy in a small volume. More specifically, one gram of uranium 235 yields more energy than one tonne of conventional fuel.

Technicatome developed the Barracuda reactor in partnership with the French atomic energy commission (CEA). Although the power rating remains classified, the reactor is understood to be more compact (i.e. higher energy density), to offer greater endurance, and to comply with civilian nuclear power safety standards. High availability will allow the Navy to extend the interval between scheduled refuelling overhauls to ten years, compared with seven to eight for the current generation. With the time required for annual maintenance down to just ten weeks and no need for intermediate refits between refuelling overhauls, availability will be significantly higher. While the Navy will have the same number of Suffren-class boats as it currently has with the Rubis class, the higher availability (estimated at over 270 days/year) will enable it to meet increasing operational requirements.

 

A nuclear powerplant subassembly in the workshop (© Technicatome / CEA)

Nuclear powerplant, installing the steam generator prior to workshop testing (© Technicatome / CEA)

 

With an all-up weight of around 400t, the powerplant is installed in a dedicated section of the hull. “We have packed an extraordinary amount of equipment into a hull section that is just 10m in length and just under 9m in diameter. This section comprises around 15,000 items plus 2km of pipework and 2km of cabling, while the design and development phase represented 8 million hours’ work,” says Loïc Rocard. “Bearing in mind that the crew will live and work within 10m of the powerplant, its integration in compliance with the relevant radiation protection requirements was a real challenge. The operating conditions are also very different from those for civilian reactors given that the powerplant must respond promptly to changes of speed, and the like. The need to power up from standstill to full speed has no equivalent in a civilian powerplants,” says Bernard Gauducheau, Technicatome’s head of defence reactors.

Propulsion system

The energy released by the nuclear fuel heats the fluid in the primary circuit (totally isolated from the fuel) which, in turn, heats the water in the secondary circuit (also totally isolated from the primary circuit), converting it into steam. This steam is fed to the ‘hybrid’ propulsion system, a key innovation compared with the Rubis class. The system’s key feature is a silent yet highly responsive electric mode for tactical manoeuvres at low and medium speeds. In this mode, the steam drives two Thermodyn-Jeumont turbo-alternators powering a pair of electric propulsion motors supplied by the ECA group. These motors drive the shaft and pump-jet via a reduction gear to offer quiet power. In the second mode, steam is fed to the Thermodyn propulsion turbine driving the shaft and pump-jet directly. This mode offers more power, but is less quiet. Man diesels and two battery packs provide backup power. While the sub’s maximum speed remains classified, published documents suggest that it is probably in excess of 25 knots. The design team claims that the sub’s ‘tactical speed’ – or the maximum speed at which discretion remains optimal, clearly a critical stealth parameter – is about twice that of the Rubis class.

 

Testing the Barracuda hull in the tow tanks at the DGA’s Val de Reuil facility (© DGA)

 

Advanced hull form

The Barracuda’s hull is optimised for minimum turbulence and hydrodynamic noise at all speeds. Detailed numerical modelling studies were supplemented, beginning in 2000, by physical model studies at the DGA’s Val de Reuil facility, the largest of its type in Europe, featuring a 600-metre towing tank, a wave tank and a hydrodynamic tunnel.

Further tests were conducted using a larger model (ML1) at a DGA facility on a lake . Here, the hull’s manœuvrability and dive safety were tested over a period of 75 weeks. “We carried out a number of simulation studies to evaluate the hull's hydrodynamics, manoeuvring performance and discretion while taking into account the key features of the overall design and propulsion system,” says a DGA engineer. Between 2009 and 2015, the DGA also conducted 225 weapon launch tests along with other tests, including countermeasures.

 

Test using the ML1 model on lake Castillon (© DGA)

Test using the ML1 model on lake Castillon (© DGA)

Test results (© DGA)

 

New steering gear

To improve the Barracuda's discretion and manoeuvrability, particularly in coastal waters and when deploying combat swimmers and their equipment, Naval Group, like other submarine design teams, has adopted X-form aft control planes. This configuration offers more precise and more responsive steering plus faster turns, both critical when executing evasive manoeuvres. The hull is also equipped with forward dive planes, replacing those on the sails** of the Le Triomphant and Rubis classes. When not in use, the forward dive planes are retracted to reduce turbulence and drag. Overall, the Suffren class will be “ten times quieter than the Rubis class,” says Admiral Prazuck.

 

Barracuda pump-jet and X-form control planes (© Naval Group)

SSN Suffren leaving the Laubeuf assembly hall on hydraulic ‘walkers’ (© Reuters)

 

Acoustic superiority: detect before you are detected

While discretion is vital, a sub’s ability to listen to its environment is equally important. “When confronting an adversary, submariners want the acoustic upper hand, which is to say the ability to detect before they are detected. This calls for a combination of optimal intrinsic discretion, high-performance sonars and crew know-how,” says Captain Bertrand Dumoulin, who commanded SSN Perle and SSBN Le Terrible.

One of the main challenges of the Barracuda program was the development of a new sonar suite, a task entrusted to Thales. Here too, the design teams built on France’s SSBN and SSN programs to improve the new class’s capabilities. “It’s another case of innovation through continuity. We started with the capabilities of the Rubis class and worked up from there. The fact that the larger hull can accommodate larger sonars is a benefit. Sonar component technologies having improved between the two generations, performance per unit area is higher. New digital technologies and new processing systems also contribute to improved listening,” says Marc Delorme, head of Thales’s sonar product line, and Gilles Baulard, Thales’s program manager for Barracuda sonars.

 

Systems supplied by Thales (© Thales)

 

Bow and flank arrays

The Suffren’s sonar suite comprises several arrays, each in its own place and each covering its own frequency range. Given that the basic concept underlying submarine operations is not to be heard or located, hence not to transmit, all but one of the arrays are passive. First, there is a new cylindrical array under a dome on the lower bow. The CA is larger than that carried by the Rubis class and uses a more advanced technology offering improved sensitivity. Next come the new flank arrays. For obvious reasons, the FAs and pump-jet remained veiled for the Suffren unveiling ceremony. The FA surface area is more than double that of the Rubis class. While these sensors were developed for the Barracuda program, smaller versions are already available for Rubis class upgrades. These all-digital arrays replace the analogue sensors on older subs. The FAs proper are planar arrays incorporated into thick panels mounted on the outer hull. They are flexible enough to conform to the hull’s cylindrical shape and can be readily removed for maintenance. Additional benefits include zero impact on ballast calculations and hull hydrodynamics as well as zero additional noise. The sensors are moulded into rubbery plates, each with its own electronic module that converts the sensor output signal directly into digital format then forwards it to the main sonar computer. After processing, the output signals are converted into video and audio formats compatible with the ops room consoles.

 

Veiled flank array (© Mer et Marine – Vincent Groizeleau)

 

Digital sensors and improved performance

Smaller new-generation digital sensors – combined with more powerful data processing that can handle data from multiple arrays and directly display the information operators need – significantly improve a sub’s capacity to detect sound, determine the source’s bearing and range, then compute its heading and speed by triangulation. Another benefit of these arrays is that they can analyse extremely short transient signals and identify the source. The system runs frequency analyses on the sea noise it picks up then cross-compares the results with databases compiled over many years by CIRA, the Navy’s centre for reconnaissance and data interpretation and analysis. The Navy’s famous ‘golden ears’ sonar operators – the last link in the chain of steps to detect signals and classify tracks – are all CIRA analysts. Despite immense technological progress, nothing has yet been developed that can interpret the most complex signals as well as a pair of gifted, well-trained ears. “New capabilities like raw signal storage and replay significantly improve data classification and analysis. The aim is to advance data processing and analysis by taking full advantage of the transition to all-digital systems and vastly larger quantities of data. This can only be achieved using tools to extract the information operators need by quickly filtering out less relevant data. Every aspect of the system has been reviewed and refined with this in mind. By presenting the right information at the right time, the system helps operators to do a better job.”

 

A CIRA technician conducting tests (© French Navy)

 

Intercept and towed arrays

The Suffren is equipped with new-generation passive arrays designed to intercept signals from active transmitters, including sonars and sonobuoys used by surface vessels and aircraft on anti-submarine patrol, and by incoming torpedoes with acoustic heads. The intercept arrays are located under small bulges on the hull, the upper portion of the sail, and under the forward keel.

The Suffren will also carry a passive towed array or ‘streamer’. Initially, the new boat will use the same type of towed array as the Rubis class. Later, this will be replaced by a new-generation device currently under development. It is not known at this stage whether this will be a reelable array or the clip-on type.

Mine and obstacle avoidance sonar

As mentioned above, all of the Suffren’s sonars except one are passive. The exception is the mine & obstacle avoidance sonar, or MOAS. The T-shaped MOAS array is located above the CA between the launch tubes. Provided as a safety feature, its job is to map the volume of water directly ahead. When operating in unknown, shallow or potentially hostile waters, it can detect moored mines and other obstacles, giving the crew time to respond. Recourse to an active sonar obviously compromises the boat’s acoustic discretion to some extent. The risk is minimised, however, by restricting the beam to a limited volume of water and by using a high frequency to benefit from the fact that higher frequency sound waves are rapidly attenuated in seawater. The underwater telephone, also supplied by Thales, is based on the same principle. The telephone offers voice and data links to surface vessels and other submarines over ranges of up to several kilometres.

 

SSN Suffren’s sail with the optronic search mast deployed (© Mer et Marine – Vincent Groizeleau)

 

Optronic masts

Additional sensors are mounted on the Suffren’s three masts, all supplied by Safran. A Series 30 optronic search mast and an optronic attack mast, or MOA, replace the traditional optical periscopes. The third mast carries the radar antenna. The search mast, or MOV, is equipped with an HDTV camera, a thermal imaging camera, a video camera with low-light amplification, and a backup camera. Although an earlier design called for two MOVs, the final spec only called for one. The MOV’s cameras rotate at high speed to provide 360° panoramic vision for surface and aerial surveillance. The MOA is also equipped with various cameras. With a diameter of around just 15cm, this mast is much slimmer than the others in order to limit surface drag, visibility, wake and the radar signature. Radar electronic support measures (RESM) modules are mounted on top of each optronic mast. Note, too, that in line with current French Navy doctrine, the optronic masts do not include laser rangefinders.

 

 

The Safran Series 10 CSR radar is provided for navigation and, if necessary, surface target detection. The optronic masts are made of titanium and the radar mast of stainless steel. All three need to be strong and stiff to allow deployment at depths of 10m or more and to withstand the considerable forces due to the sub’s speed, currents, waves and wind, the last three being especially important in bad weather. The masts are coated with a radar absorbent material to minimise the risk of detection by enemy radars.

 

Mockup of a Scorpène sail with search, attack and radar masts up (© Safran – Adrien Daste)

 

Non-penetrating too

All three masts feature non-penetrating designs, another first for a French Navy sub. Gone are the days when the commander rotated an optical periscope to observe the surface environs after activating a hydraulic mechanism to raise it. From now on, surface imagery will be transmitted in real time to consoles and the ops room tactical table where it can be viewed by several people at once.

 

Components, assemblies, systems, etc. (© diagram Naval Group / photo Mer et Marine)

 

More freedom, optimised layout

With penetrating masts and periscopes, the only option was to place the ops room directly under the sail. The move to masts that do not penetrate the pressure hull gave the design team new freedom when it came to the location, layout and optimisation of the ops room. This new-found freedom resulted in more space for personnel to move around and an ops room that is now just aft of the sail. This led to improvements in the crew’s living and working conditions. “The crew’s quarters have benefited from far greater attention to detail, including input from a specialist with experience in designing passenger accommodation for cruise ships. We worked hard to create the best possible crew conditions, despite the limited space. Each crew member has access to a private space, light levels can be varied, the bunks are more spacious, and the environment pleasant,” says Vincent Martinot-Lagarde, Naval Group’s Barracuda program manager. Apart from the commander, who has an individual cabin, the crew share two-, four- and six-bunk cabins. The layout also accommodates female crew members in line with a change initiated on the Navy’s SSBNs in 2018.

 

Suffren crew cabin mockup (© Mer et Marine – Matthias Esperandieu)

Another important change in the layout concerns the main propulsion control room for operators monitoring the electric and nuclear powerplants and the propulsion system. Previously located in the aft section close to the reactor compartment, this is now next to the ops room. With most of the controls being automated and now part of the integrated platform management system (IPMS), the propulsion control room normally requires just two operators.

Advanced automation and fewer sailors

Thanks to advanced automation combined with automatic backups and manual emergency controls for critical systems, the Suffren takes reduced crewing to a new level with a complement of ‘61 (+2)’ comprising 12 officers, 49 sailors and two ‘golden ears’ sonar operators. This is fewer than the ‘68 (+2)’ aboard the smaller Rubis class.

In line with the Navy’s normal practice, the Suffren’s crew will work as two shifts, known as the Blue and Red shifts. Additional personnel will take part in the shakedown cruise and other early operations. When the program was launched, the first spec called for a crew of 60 plus accommodation for ten passengers or commandos. Lessons learned by the French Navy over the last few years from deployments involving Mistral-class landing helicopter docks and FREMM frigates having shown that ‘over-optimised’ crewing levels can be counterproductive, the standard complement for the Suffren class was increased slightly by reducing the number of bunks for passengers or commandos. Should the need arise, space for a total of ten extras will be found by cramping the space of some. Finding space for ten commandos on a special operations mission should not be too difficult given that such missions are typically short and commandos are used to lower levels of comfort.

 

Barracuda with dry deck shelter (DDS) aft of sail (© Naval Group / DGA)

 

Special operations, a new priority

For the French Navy, one of the key benefits of the Suffren class is the provision for special operations. Whereas their predecessors were designed primarily as hunter-killers, the new class accommodates commandos as one of its main missions. But this nearly wasn’t the case. Back in the 1990s when French specialists first began thinking about the successors to the Rubis class, a number of concepts were aired. One envisaged a 9000-tonne sub with vertical launchers for cruise missiles, but none saw special operations as a high priority. A handful of engineers and sailors did see the need, however, and argued for design provisions for such a capability. The post-Cold War period, among other events, proved them right and the said provisions were duly made.

 

Barracuda, new operational capabilities (© diagram Naval Group / photo Mer et Marine)

 

Dry deck shelter

In addition to providing space for special forces and their gear, the Suffren class will also carry a swimmer deployment vehicle, or SDV, making life far easier for commandos than when the only way in or out was through the torpedo tubes. In particular, the new boats will be able to carry a dry deck shelter (DDS) aft of the sail. This removable module, developed and built by Naval Group, is designed to meet the needs of navy commandos. It is 11m long by 3m in diameter, weighs around 40 tonnes, and is made of ultra-tough steel to withstand the pressure at all depths within the sub’s normal envelope. The outer surface has a composite coating designed to minimise interference with the host’s normal hydrodynamics and impact on the host’s acoustic discretion. The interior remains dry during transits and mission preparation. Commandos enter and leave the DDS through a transfer trunk communicating with a dedicated space inside the sub’s hull. The DDS can also accommodate a range of payloads, including autonomous underwater vehicles (AUVs) and the new PSM3G swimmer delivery vehicle.

 

DDS with PSM3G swimmer delivery vehicle (© French Navy)

PSM3G swimmer delivery vehicle leaving the DDS (© Naval Group)

 

New swimmer delivery vehicle

The PSM3G third-generation SDV was developed by the ECA group and designed by the French Navy’s Hubert combat swimmers squad based at Saint-Mandrier near Toulon. The prototype has already completed initial sea trials. Deployable from the coast, a surface vessel or an SSN, the new type will replace the current Coryphène type. The PSM3G is bigger, quieter and offers higher performance than its predecessor, including increased payload capacity and endurance. The Navy says that it can carry “up to ten combat swimmers, including the driver” and offers “revolutionary operational capabilities compared with its predecessor”. It is designed to “infiltrate with the utmost discretion”, making it the “the ideal tool against naval denial of access tactics”.

 

Mockup of PSM3G on ECA stand at Euronaval 2014 (DR)

Mockup of PSM3G on ECA stand at Euronaval 2014 (DR)

 

The Navy has ordered two PSM3G vehicles and two DDSs to be mounted on any of the six Suffren-class boats, as required. Note too that a sub will not be obliged to return to Toulon, its home port, to be fitted with a DDS as this operation can be executed in any friendly port. Given that the DDS is transportable using aircraft like the C130, it can be shipped to any distant theatre of operations accessible to an SSN, then installed in a friendly port or even at sea if the appropriate facilities are available. In addition to the two DDSs under construction, the Navy has also ordered a training module.

Aside from Navy combat swimmers (on offensive, intelligence or logistical missions), the PSM3G will also be used by swimmers deployed by the DGSE, France’s external security agency. A French senate report published in 2014 made clear that some DGSE operatives are “trained and qualified in the same way as Hubert squad combat swimmers and capable of performing the same tasks. While the job is different, the skills required are similar.”

Only four countries – France, the USA, Russia and the UK – deploy SSNs equipped with both DDSs and SDVs.

 

Test firing, MdCN submarine-launched cruise missile, 2012 (© DGA)

 

20 weapons, including cruise missiles

Suffren-class boats have four 533-mm launch tubes in the bow section and a payload capacity of 20 weapons (not counting any in the tubes), including heavyweight torpedoes, anti-ship missiles and cruise missiles. This is twice the payload capacity of the Rubis class.

The payload will include the MdCN cruise missile developed by MBDA and offering an unprecedented deep strike capability. This weapon, the first of its type to be developed in Europe, represents a major innovation in France’s offensive arsenal. The MdCN can strike targets up to around 1000km away from a safe standoff range, typically in international waters, and well beyond the reach of any weapons deployed by most adversaries. The missile is 7m in length, including the booster, and weighs around 2 tonnes. This fire-and-forget weapon deploys its wings seconds after launch, flies at around 1000km/h and uses multiple modes of navigation. During the flight phase, the inertial platform, radio altimeter and satellite navigation system constantly update key data enabling the missile to fly a precise course at low altitude. During the approach phase, an IR seeker guides the warhead to within a metre or so of its target. The advanced warhead is designed to knock out strategic targets, including those in hardened shelters.

 

MdCN test firing from a FREMM frigate (© French Navy)

 

The MdCN is available in two variants. The vertical-launch version is carried by the Navy’s FREMM frigates (up to 16 per ship) and has been operational since 2015. This version was fired in a combat situation for the first time off the Syrian coast in April 2018. The submarine-launched version is housed in a capsule launched from a weapon tube, enabling an SSN to fire up to four in quick succession. The moment the capsule is ejected, the booster fires and capsule and missile speed to the surface. The capsule then jettisoned while the booster continues to accelerate the missile to a speed at which the booster is also jettisoned, the turbojet takes over propulsion, and the air inlet scoop and wings are deployed. From the moment the sea-to-air transition capsule is jettisoned, the firing sequence is the same as for the surface vessel vertical-launch variant.

 

Video, MdCN submarine-launched cruise missile (© MBDA)

 

The first complete MdCN firing was from the DGA’s Squale underwater test facility at its Levant missile test site on the Mediterranean after the facility had been reconfigured to simulate SSN launch conditions. This test firing, in October 2012, was the fourth of the MdCN development phase. It successfully demonstrated missile flight control and navigation, validated terminal phase satellite guidance, and completed the validation of the IR guidance phase first tested by an earlier firing in July 2012. Final qualification of the MdCN submarine-launched cruise missile will be conducted by the Suffren following the boat’s formal acceptance by the DGA and the Navy, which is currently scheduled for mid-2020.

Using FREMM frigates and Suffren-class SSNs as complementary MdCN cruise missile launch platforms, the French fleet will be able to undertake actions on a much larger scale and to achieve a wider variety of effects, depending on whether the aim is to overtly threaten or instil doubt. ‘Visible’ surface combatants can be used to apply direct pressure on an adversary by tailoring the scale of the operation to the situation and the level of determination. Conversely, submarines, which are ‘invisible’ and hence more insidious, instil doubt in the enemy's mind and retain the element of surprise.

 

Computer graphic, F21 torpedo launch test from a Scorpène SSK (© Naval Group)

 

F21 heavyweight torpedo

The Suffren will carry the F21 new-generation heavyweight torpedo which replaces the F17Mod2. Naval Group will deliver the first batches of F21s, for both SSNs and SSBNs, to the Navy later this year under the DGA’s Artémis program. The F21 is 533mm in diameter, 6m long and weighs 1.5t. Thales Underwater Systems worked with Naval Group to develop the acoustic systems, while Saft provided battery expertise and Eurenco developed the warhead. Designed for use in both the open ocean and littoral waters, the F21 can be fired in (fibre-optic) wire-guided mode or in autonomous mode and is effective at depths from less than 10m to more than 500m. The advanced acoustic head offers improved search performance in all environments, including shallow water where noise levels are high, and against enemy countermeasures.

 

A type F21 torpedo ready for testing (© Naval Group)

 

The F21 uses a pair of contra-rotating multi-blade propellers. With a top speed in excess of 50kts and an endurance of around an hour, it has an effective range of over 50km. The design owes its impressive endurance to its primary power source which uses silver oxide-aluminium (AgO-Al) thermal batteries. AgO-Al offers a far higher energy density than conventional Ag-Zn batteries, resulting in greater range and more effective use of energy. This configuration enables the F21 to approach its target quietly before switching to full power and full speed for the attack phase. After more than 10 years’ R&D by Naval Group and its partners, this technology has been amply demonstrated by the success of the MU90 lightweight torpedo program.

 

A submarine-launched Exocet SM39 emerges from below still in its capsule (© MBDA)

 

Exocet and mines

Like its predecessors, the Suffren class will carry the SM39 anti-ship missile, a submarine launched version of MBDA’s celebrated Exocet. This fire-and-forget weapon is 4.7m in length and weighs over 600kg. It is stored and launched in a pressurised watertight capsule and equipped with an RF seeker for terminal guidance. Like the MdCN, it is ejected from a launch tube then boosted to the surface, where it jettisons its capsule and heads for its target. Flying at Mach 1, it has a range of around 50km. The Suffren class will carry the latest version, the SM39Block2Mod2.

With just a few minor changes, the Suffren class can also be equipped to lay mines. The FG29, the Navy’s current type, will be replaced by a new type in due course.

Shared CMS

A Sycobs combat management system, or CMS, developed by Naval Group manages the Suffren’s sensor suite and weapons systems. A version of this CMS is in use on SSBN Le Terrible, in service since 2010, and on the Le Vigilant, Le Triomphant and Le Téméraire since their refits in 2013, 2016 and 2018, respectively. The new Sycobs CMS is more powerful and offers a wider range of functions than its predecessor, along with improved operator-machine interfaces with all system data and functions accessible to all operators at multifunction consoles. The SSN ops room also features a digital tactical table to display the sub’s tactical situation and other information, including video imagery recorded by the cameras on the optronic masts. “The tactical table reminds some of the space shuttle’s control panel! It is far bigger than previous sub displays and presents a selection of essential information. Much less information is passed around the ops room by word of mouth and much more is presented graphically. The tactical table displays a snapshot of the sub’s status and operational situation. Every aspect his highly automated. The controls and consoles are all-digital and the interfaces more intuitive,” says Axel Roche, the Suffren’s first commander (see also Axel Roche, premier pacha du Suffren: « C’est le meilleur sous-marin au monde ! »).

 

Suffren ops room, President Macron and others at tactical table (© AFP – Ludovic Morin)

Suffren ops room, President Macron and others at tactical table (© AFP – Ludovic Morin)

 

Torpedo countermeasures

The combat system also manages the sub’s torpedo decoys. The Suffren class is equipped with the new Némésis system, a version of Naval Group’s Contralto system, using Canto-S decoys. Instead of the earlier ‘seduction/distraction’ principle using a combination of stationary and moving decoys, Némésis is based on a ‘dilution’ concept by having the decoys transmit a multitude of fake echoes that are credible enough to saturate and confuse the in-coming torpedo’s processor. The moment an approaching torpedo is detected, Némésis launches a salvo of decoys while simultaneously presenting the operator with tactical options including evasive manoeuvres.

 

Schematic, Contralto torpedo countermeasures system (© Naval Group)

 

Inertial navigation system

Deep in the sea and far from home, a vessel needs to know precisely where it is at all times. This is especially true in the case of nuclear-powered subs given that they remain submerged for so long. With no landmarks to steer by, the only options would appear to be to scan the night sky from periscope depth or record imagery of the seafloor and compare it with charts compiled by SHOM, the French Naval Hydrographic & Oceanographic Service. SHOM charts and data for patrol areas are, moreover, vital for safe navigation and optimal sonar performance.

To preserve its efficiency and autonomy, a sub cannot depend on external systems such as GPS satellites. Satellite navigation systems can, in any case, be switched off, deliberately scrambled or disturbed by solar flares. And they can be jammed or fail. Their coverage is also incomplete and, last but not least, their signals do not penetrate water, making them of little use to a submerged submarine. It is for all these reasons that navies use inertial navigation systems. INSs accurately and continuously determine their position in space by integrating motion over time. They do this using gyroscopes to determine the platform’s attitude by measuring rotation effects and accelerometers to measure accelerations. Algorithms then determine the platform’s position relative to its point of departure as a function of various parameters, including speed, altitude, heading, roll and pitch. Precision location data is essential not only to navigate and ensure a warship’s safety, but also to guarantee the accuracy of its weapons.

The Suffren is equipped with two Sigma 40XP laser gyro-type INSs supplied by Safran and based on the ring laser gyroscope, or RLG, technology.

Communications suite

The communications suite comprises a number of secure systems, including tactical data links ensuring interoperability with international forces. Each system is fully backed up. Thales supplies all the radio equipment required to transmit and receive mission orders and reports. These systems use frequencies from all ranges from VLF to UHF, enabling the boat to communicate with a shore command centre and with other naval force units. Thales also supplies the Navy’s shore-based transmission centres to provide end-to-end communications between the command centre and the submarine.

The Suffren’s satellite communications system, also supplied by Thales, is part of the joint forces’ Syracuse III ground segment: "These links meet the Navy’s strategic communications needs by incorporating a DiveSat antenna system designed specifically for submarines and closely coupled to the Syracuse joint ground network. They also meet the relevant capacity requirements. Satellite communications are a key component of collaborative combat given that interoperability and mobility are essential in modern-day military operations. These Thales systems give the Navy the secure, ECCM (electronic counter-countermeasures), end-to-end, long-distance communications it needs. This is achieved using a highly secure System21 transmission system,” says a Thales engineer. Suffren-class boats will subsequently be equipped, like the rest of the French fleet, with the planned Syracuse IV system as soon as it is available. This system will offer improved availability and performance, including greater discretion and higher capacity.

Deeper and deeper

Suffren-class hulls are fabricated using high-yield-strength weldable steel to the 80HLES standard, a French variant of the HY-100 standard specified for the hulls of the US Navy’s Seawolf- and Virginia-class SSNs. Barracuda hulls are designed to operate at greater depths than those of the type’s forebears. The published data for the Rubis class mention a dive depth of 300m. For the Barracuda type, the figure is probably in excess of 350m. Note, however, that the hull crushing depth is far greater for both types. Diving beyond the maximum operating depth should only be undertaken in extreme emergencies given the risk of serious and even irreparable damage.

 

SSN Suffren, grinding a hull section weld (© Naval Group)

 

Next, sea trials in 2020

The order for the Suffren was placed in 2006 and the first steel cut in 2007. The boat left the Laubeuf assembly hall at Naval Group’s Cherbourg yard in July 2019 on 24 hydraulic 'walkers'. It then took two days to walk it to the DME dock and shiplift. The dock was flooded and the Suffren set afloat on Friday 2 August.

 

SSN Suffren on hydraulic ‘walkers’ as it leaves the Laubeuf assembly hall (© Reuters)

 

Time-lapse video of SSN Suffren leaving the Laubeuf assembly hall (© Naval Group)

 

“Some 90% of the shipboard systems were tested before the boat left the assembly hall. The only items still to be tested are those that could not be switched on in the assembly hall for technical reasons,” says Vincent Martinot-Lagarde. To speed up the process, Naval Group tested as many systems as possible ahead of time using system prototypes and shore integration facilities. The CMS and other key systems were tested using control-command systems. “We have also invested a great deal in IT, including a second virtual reality room complete with a total immersion space to enable integration teams to familiarise themselves in advance with challenging tasks in confined spaces. Digital models of the entire submarine are accessible using Box3D consoles located near different work areas. We are also using virtual reality more to check outfitting procedures and tactile tablets for quality control. Many of these tools were used for the first time to build the Suffren. Their use will now be ramped up for the construction of the second and third boats,” says Naval Group’s Barracuda program manager.

 

A technician practicing a task in a virtual reality room (© Naval Group)

 

With the Suffren now afloat, work will begin on a series of quayside tests, as well as underwater testing at increasing depths, including leaktightness, seawater connections, cooling systems, launch tube operation, communications suite, and combat system. Fuelling of the nuclear reactor will begin in September 2019 followed by reactor startup (divergence) in November and December. Initial sea trials are scheduled for Q1 2020. These will include surface tests off Cherbourg, followed by platform tests off Brest in Q2, then combat system tests off Toulon where the Suffren class will be based. If all goes well, the DGA should formally take delivery of the Suffren in Q3 2020. The boat will then be transferred to the Navy which will validate its military capabilities with the DGA’s assistance, including MdCN and F21 firing tests. The Suffren will enter active service following a shakedown cruise and a final round of fine-tuning. The date of commissioning has yet to be announced.

 

Barracuda simulator, trainees at the controls (© French Navy)

 

Highly experienced first crew

The Barracuda simulator developed for crew training features a control compartment that can tilt 30° to simulate the sorts of manoeuvres required when hunting down an enemy sub. Candidates for the Suffren crew have been in training for some time (see Inauguration des simulateurs des futurs SNA du type Barracuda). The crew for the sea trials was announced on 11 July. This combined commissioning and test crew includes some of the Navy’s most experienced personnel. This crew has an average age of 33 and an average of 8500 hours’ submerged service, compared with 28 and 6500 hours for a normal Rubis-class crew. The first Suffren crew will be led by Commander Axel Roche who previously served on SSNs Rubis and Saphir. The commissioning crew of 90 will be larger than the operations crew of 68 (+2). Given the high workload and tension, crew members need to take regular breaks during sea trials. For some tests, the crew will be joined by employees of major contractors and/or DGA personnel.

 

Suffren unveiling, Cherbourg, 12 July, members of first crew (© Mer et Marine – Vincent Groizeleau)

 

Sixth-of-class ordered

With the first four boats of the Suffren class already under construction, President Emmanuel Macron’s announcement concerning the order for the sixth-of-class boat at the Suffren unveiling ceremony in Cherbourg on 12 July was most welcome. SSNs Duguay-Trouin, Tourville and De Grasse are scheduled for delivery under France’s current defence spending plan ending in 2025. The actual dates have yet to be announced as the contractors and the Ministry of Armed Forces have agreed to an adjustable delivery plan offering several months’ flexibility if needed. Given that the provisional schedule lists several dates late in the different years, some boats may only be delivered in the following year. It therefore appears likely that the Duguay-Trouin will be delivered between late 2021 and early 2022, the Tourville in 2023/2024, and the De Grasse in 2025/2026. On the other hand, the Navy and Naval Group are both confident that SSNs Rubis and Casabianca, the fifth and sixth of the class, will join the fleet in 2027 and 2029, respectively. The construction of the second-of-class Duguay-Trouin is on schedule. The centre and bow sections are in the Laubeuf assembly hall and will soon be joined by the aft section in the area previously occupied by the Suffren. It is here that the three sections will be welded together.

 

Bow of SSN Duguay-Trouin in the Laubeuf assembly hall (© Mer et Marine – Vincent Groizeleau)

SSN Suffren under construction alongside two sections of SSN Duguay-Trouin, Laubeuf assembly hall, late 2018 (© Naval Group)

Bow section of SSN Duguay-Trouin with launch tubes, Laubeuf assembly hall, late 2018 (© Naval Group)

 

First Rubis retired

In early July, SSN Saphir, the first of the Rubis class, which entered service in 1984, docked in Cherbourg to be decommissioned. In December 2020, the next in line, SSN Rubis, commissioned in 1983, will dock at a facility on the tip of the Cotentin peninsula to have its reactor dismantled before proceeding to another facility where the hull will be broken up. The other Rubis-class boats will be decommissioned and dismantled as the Suffren-class boats enter service. The Casabianca was commissioned in 1987, the Émeraude in 1988, the Améthyste in 1992 and the Perle in 1993.

 

SSN Saphir entering Cherbourg harbour, early July 2019 (© French Navy)

 

Sub #108

The Suffren is the 108th sub to be built in Cherbourg since 1899. The first was the Morse followed promptly by the Narval designed by engineer Maxime Laubeuf. Since the 1960s, the yard has produced 17 nuclear-powered boats (six for the Le Redoutable class; six for the Rubis class; four for the Le Triomphant class; and one for the Suffren class) plus a number of diesel-electric boats for international clients. The Suffren class presented the yard with a number of engineering and industrial challenges that, as President Macron said, are beyond the reach of all but a handful of countries. The Barracuda program represents an investment of €9.1 billion for the design development and the construction of six boats plus the purchase of long-lead-time spares. Each boat comprises over 700,000 components, 70,000 assemblies, 500 systems and subsystems, 200 IT programs, 21 million lines of code, 20km of pipework and 150km of cabling.

 

Suffren unveiling, Cherbourg, 12 July (© Mer et Marine – Vincent Groizeleau)

SSN Suffren under construction in the Laubeuf assembly hall (© Naval Group)

 

800 contractors and 10,000 employees

Over 10,000 employees of contractors, including Naval Group and Technicatome, government departments, the DGA and the CEA have already contributed to the program, logging 50 million hours’ work while employees of some 800 subcontractors all over France have contributed a further 20 million hours. “Programs like this are extraordinary adventures combining human and technical challenges. To see the Suffren finished and ready to come to life is a source of great pride for all concerned, from those completing their last project before retirement to those who came aboard at the very start. Today, all can see the fruit of a team effort and a decade of collaboration drawing on the skills and expertise of Naval Group and its partners,” said Vincent Martinot-Lagarde. And the adventure continues, not only with the Suffren and its sisterships, but soon with an even bigger challenge, namely the design and construction of third-generation SSBNs with the first cut for the first of class scheduled for 2023 followed by its entry into service by around 2030.

by Vincent Groizeleau. Translated and adapted by Steve Dyson.
French version (Suffren: gros plan sur le nouveau SNA français) published online on 19 July 2019.

* SSN Suffren is named after Pierre André de Suffren, vice-admiral of the French Navy in the 18th century

** While non-specialists may be more familiar with the term ‘conning tower’, submariners generally call this structure the ‘sail’, confusing though that may sound to some.

 

Video, SSN Suffren leaving the Laubeuf assembly hall (© Naval Group)

Aerial view of Naval Group’s Cherbourg shipyard (© Naval Group)

SSN Suffren ready to leave the Laubeuf assembly hall (© Reuters)