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Stealth technology aims at minimizing a vessel's transmitted and reflected energies – heat, light, sound, electric potential, and electromagnetic radiation – to deny an opponent the opportunity to locate, identify, track, and attack it. Disguise has always been an essential aspect of warfare.

HMS “Nyköping” on the shipyard the day before launching on August 18, 2005.

Advanced stealth technology gives Visby corvettes the edge

By Kjell Göthe, senior vice president, PR & Communications, Kockums AB
kjell.gothe@kockums.se

The Swedish Navy has always operated in shallow “littoral” waters, in which it is highly specialised. After the events of September 11th 2001, that redefined the global threat scenario, the Swedish Navy’s strategy for coastal surveillance and defence (the Maritime security concept) has attracted growing international attention. This is also attributable to the fact that the new Visby-class corvettes, which Kockums is building for the Swedish Navy – and which feature full stealth capability – are ideally configured to meet the new threat scenario. The vessels, constructed in fibre-reinforced plastic (FRP), are extremely difficult to detect, either with radar or other sophisticated techniques.

As first-of-class, HMS Visby, launched in 2000 and christened by King Carl XVI Gustaf, has given its name to this series of vessels. Most of the technology has been developed in Sweden, in close collaboration with the Swedish Defence Forces, the Swedish Defence Materiel Administration (FMV), the Swedish Defence Research Agency (FOI), Swedish and foreign industrial corporations, as well as in association with experts at several universities and institutes of technology.

FMV is prime contractor for the Visby system. The vessels are designed and supplied by Kockums AB. Command, control and communications (C3) systems – and some weapon systems – are supplied by Saab. The guns are from Bofors Defence, the surveillance radar from Ericsson Microwave Systems and the ASW and mine clearance systems from General Dynamics Canada. Some one hundred subcontractors are engaged in the project.

HMS Visby is the first-of-series, followed by HMS Helsingborg, HMS Härnösand, HMS Nyköping and HMS Karlstad. Its multirole capability and the fact that it can be deployed to exert varying degrees of force, depending on circumstances, guarantee the Visby-class corvette a vital future role, not least as part of the rapid reaction force currently being built up by Sweden.

The traditional strength of naval forces is that they can be mobilised quickly and that, once on station, can carry out their task continuously and for an extended period. To do this, they must control the entire marine theatre – not only on and below the surface, but in the skies above too. Multi-mission capability when on station is also important, including stealth ability, as and when required.

Multirole capability a plus
One key reason behind the Visby project was the need to stop the constantly spiralling cost of new naval vessels. This goal has been achieved, a key factor being their flexibility and multirole capability, enabling them to conduct a broad range of different missions, from mine clearance, anti-submarine warfare (ASW), surface combat, marine surveillance and shipping protection to support for civilian emergency/relief services, as in accidents at sea and, last but not least, participation in international missions. In the same way that Sweden’s advanced JAS (air superiority/strike/reconnaissance) fighter assures the Swedish Air Force of true multirole capability, the Swedish Navy’s new Visby corvettes offer unequalled flexibility.

Multifunctionality and interoperability offer major benefits in terms of modern netcentric defence thinking: flexible units have a better chance of responding to new threats and missions. This can be invaluable, since nobody can predict how a specific crisis may develop.

A view over Kockums shipyard in Karlskrona with the modern Visby corvette and the old mast crane.

Full stealth capability
“Stealth” or signature-reduction technology is really nothing new in the defence context. The ability to merge into the surroundings and become as close to invisible as possible has always been a good way to gain a strategic advantage. The submarine can lurk below the surface, able to see and hear everything, even at significant distances. As part of a contingency response force, the submarine is a crucial information gatherer, although also able to carry out an operational role if so required.

Naval surface ships have long wished for the strategic benefits of stealth that have always been the trademark of submarines. We have had to wait until now, however, for the development of the technology and know-how that can bring this about in practice.

The stealth concept comprises everything that serves to minimise signatures and signals, either to enhance the vessel’s own countermeasures and sensors or to make detection and identification by an opponent more difficult – or impossible. Several benefits derive from reducing a ship’s signatures (emissions/reflections betraying its presence). The first is the enhanced performance of its own sensors in areas where its own signatures have been reduced. This is precisely the same effect we all experience with our own senses as, for example, when we find it easier to detect faint sounds if we remain silent ourselves.

If the signatures can be further reduced, the ship’s systems for fooling or confusing an enemy, known as “countermeasures”, become more effective. To achieve such an effect, the signatures a vessel emits or reflects (such as radar waves) must be significantly less than those generated by countermeasures. For a vessel in a critical combat situation, the ability to maintain signature overload in countermeasures is therefore crucial to enhance survivability.

Nearly invisible
To achieve true stealth, however, you have to go still further. Best of all, of course, would be to avoid detection at all, i.e. to be in principle invisible to every conceivable sensor. Total invisibility may not be possible, of course, but near invisibility – or at least extremely difficult to detect – can be arranged. What makes the Visby corvettes so unique is that we have achieved this low level in all signature areas. Described in the simplest terms, we have built a protective “signature screen” around the vessel, which no signatures outside our own control are allowed to penetrate. Thanks to this signature “screen”, the Visby corvettes are extremely difficult to detect.

Should the vessel be detected anyway, it will be able to withdraw relatively easily and hide again. Alternatively, the crew can utilise the vessel’s low signatures in combination with its suite of countermeasures, making it extremely difficult for smart weapons such as missiles, modern mines and torpedoes to penetrate its defences and achieve a strike.

The Visby corvette’s hull has been optimised to ensure the best possible seagoing qualities, combining excellent course stability with extreme manoeuvrability. It has been specially designed for water-jet propulsion. An extremely lightweight hull is decisive to the vessel’s overall performance and combat efficiency. To satisfy these requirements without compromising on performance specifications, the hull is of sandwich design, featuring a PVC core with a carbon fibre/vinyl ester laminate. This combines high strength and rigidity with low weight and good shock-resistance characteristics.

“Life aboard a Visby class corvette is very different compared to other naval vessels”, says second-in-command Mats Agnéus.

Highly manoeuvrable
Lieutenant-commander Mats Agnéus, RSwN, HMS Visby’s second-in-command, has been engaged in the project since 2000. In a recent interview for Kockums Nytt, he had this to say about the new vessel:

“Life aboard a Visby class corvette is very different compared to other naval vessels. She is almost twice the size of an MCMV or fast missile patrol boat, so that she rides more easily, making life more comfortable onboard”.

“Although a bigger vessel, she is highly manoeuvrable. We have operated in both the North Sea and the Baltic in 2001, 2002 and 2005, and we have also had naval conscripts aboard, doing their national service.”

Some months ago, joint trials were conducted with HMS Visby and HMS Helsingborg, to assess and document the vessels’ capabilities. These trials were covered by several photographers and film crews. Commander Anders Olovsson on HMS Visby and Commander Olof Stark on HMS Helsingborg and their crews showed off the vessels’ capabilities and demonstrated how they could manoeuvre in narrow channels and close to rocky outcrops in the littoral zone. One of the photographers was Peter Neumann, from Hamburg, possibly the world’s foremost naval photographer. ThyssenKrupp Marine Systems, the group of which Kockums is a part, is one of his clients.

The benefits of stealth
Stealth technology dramatically increases survivability in surface combat. But it is just as important that the technology provides opportunities for active response. The commander of a stealth vessel can acquire a good idea of the situation at sea without being detected until late in the game, thereby gaining a crucial time advantage compared to the other players. This time advantage can be utilised in several ways, depending on circumstances. In cases where the opponent’s intentions are unclear, a stealth vessel can refrain from shooting first. In the most extreme case, in a straightforward duel with an opponent, the time advantage can be used offensively.

In other situations, the vessel may well want to project a highly visible presence. In the context of an international peacekeeping mission, for instance, the flexing of military muscles could have a deterrent effect. For example, if the ship’s commander wants to become highly visible on radar, he can hoist a radar reflector on a special mast that can be raised and lowered and thereby temporarily eliminate the vessel’s stealth status within radar range. If a threat develops while in this situation, the commander simply lowers his mast again, and the vessel’s stealth status is instantly regained.

	One key reason behind the Visby project was the need to stop the constantly spiralling cost of new naval vessels.

Visby class corvettes carry a crew of 43 men and women, of whom 16 are conscripts. The corvettes are 72 metres long and 10.4 metres in the beam, with a draught of approximately 2.4 metres. Gross displacement (weight) is about 650 tonnes. If they had been built in steel, they would have weighed almost twice as much, severely reducing their stealth qualities.

The secret lies in the material
One of the secrets of these vessels’ advanced stealth capabilities is the material (FRP sandwich) used in their construction, which features excellent non-magnetic properties while also being difficult to detect with radar and IR (thermal imaging) sensors. It is also extremely resistant to shock, should there be an underwater explosion in the vessel’s vicinity.

The Visby corvettes are equipped with combined diesel and gas (Codag) turbine and diesel engine propulsion, providing a top speed in excess of 40 knots (more than 70 kph). The actual top speed is classified. The diesel engines develop a total of approximately 2,600 kW and the gas turbines a total of some 16,000 kW. The engines power the waterjet propulsors, which make the vessel highly manoeuvrable as well as quiet, despite its size.

To enable the vessels to fulfil their role in the new netcentric contingency response system, the Visby corvettes are equipped with modern communication systems that promote an effective interchange of information with other units, military or civil. The Visby corvette, for example, will be able to direct its fire based on target data downloaded from other units, further reducing the risk of detection as compared to reliance on stealth alone.

The introduction of the new corvettes provides the Swedish Navy with significantly increased endurance and will further improve the operational viability of its surface units. From the very start, the corvettes have been equipped to ensure smooth integration with other units of Sweden’s total defence force operating in the marine sector, ranging from the Swedish Air Force, Coast Guard and various emergency and rescue services, to customs, police and other maritime traffic. This is essential, given the fact that naval and civil units will have to collaborate much more closely in the future. The Visby corvettes will be able to act as spiders at the centre of communication and operational networks on extended maritime missions.

Maritime security concept
Sweden has established a Maritime security concept in which Kockums products play a crucial role – on and below the surface. The Swedish Navy possesses a high level of competence in its niche sector, and our products enable Sweden’s Navy and Coast Guard to operate across the entire scale of conflict, from civil to military threat, and to conduct international missions on a broad front.

“Maritime Function” is a collective term covering all utilisation of the sea. There has been a dramatic change in the threat scenario, especially with respect to the increasing threat of terrorist activity against civil maritime traffic, although pirates and smugglers/traffickers also pose a very real threat. Society must be able to respond to these threats and to provide protection, at both national and international level.

A view of the Karlskrona shipyard with the old docks that are still used.

Latest update 18-10-2006 8:49

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