Swedish Navy Mixes Evolution and Revolution to Launch Stealth Multimission Corvette

By Captain Thomas E. Engevall, Royal Swedish Navy

At the start of the development of the future Swedish generation of surface combatants (today's Visby ) a need for new thinking was apparent. The ever-increasing costs of defense equipment had to be contained. At the same time, the predicted characteristics of the future battlefield set high demands on one's own sensors and weapon systems. Together, these two facts present a tricky equation. The Swedish answer to that problem has become the Visby -class corvettes, ships with multimission capability in combination with stealth characteristics.

Multimission Capability

For all navies that have to take budgetary considerations into account, multimission capability offers a very attractive option. It also, in a very natural way, builds on the classical strengths that naval forces possess in forms of endurance, independence, and the ability to move into or out of a theater of operations.

Visby's missions include:

  • Mine countermeasures (MCM) operations with an alternate payload for antisurface warfare
  • Antisurface warfare operations with an alternate payload for MCM
  • Antisubmarine warfare
  • Defensive/offensive mine laying
  • Patrol
  • Escort
  • International (U.N.- and/or NATO-led) peacekeeping or peace enforcement operations

Stealth and Signature Control

Among navies, stealth in itself is not new. Cover and concealment always have been used to get an upper hand against an opponent. Among submariners, stealth is natural—and the foundation for survival.

It is important to state that the choice for stealth is a rational alternative for future Swedish Navy surface ships. The main reason why the Swedish Navy has chosen stealth is that it has proved to be a very cost-effective way to meet the threats of the seas of tomorrow. Numerous predictions, simulations, and war games in combination with full-scale trials (with the Smyge and other ships) have shown the Swedish Navy that it is more beneficial to go for stealth than it is to go for "invincibility" with various advanced self-defense systems. The benefits are not only measured in economical figures but also in terms of survivability and capability of the ships' on-board systems.

The first effect of signature reduction is increased capabilities of the ship's own sensors because of a better signal noise ratio. The next effect is that the capabilities of one's own countermeasures increase. To achieve that, a certain level of signature reduction must be reached; a level where the ship's reflected or transmitted energy is substantially lower than those of the countermeasure systems. The next level to aim for is when the signatures are so low that even if it is possible to detect the ship, identification is made difficult or even impossible. The highest level of signature reduction is when the signatures from the ship are at such low levels that they are at the same level (or lower) than the environmental background noise.

Thus, stealth considerations apply under, on, and above the surface. These encompass much more than just the reduction of radar cross section (RCS). Although the effort to reduce the radar cross section to extreme low levels gives the Visby her characteristic silhouette, the reduction of RCS is just 1 of 12 areas of signature reduction on the Visby class.

The following signatures get special attention:

  • Radar cross section
  • Infrared signature
  • Magnetic signatures (direct current, alternating current, eddy current flux)
  • Hydroacoustic signature
  • Hydroacoustic target strength
  • Visual signature
  • Airborne acoustics
  • Laser cross section
  • Electrical signatures
  • Hydrodynamic pressure
  • Wake
  • Directional emitted signals

The real challenge within the project has been—and remains—to create a balanced effort in all these areas so that no weak spots appear that an adversary can exploit. One can see this process as an effort to build a homogenous signature wall for outgoing and incoming signatures. The creation of this wall demands a very tight project control during the ships' entire lifetime. A special signature coordinator with substantial authority has been placed directly under the program manager. In addition, special efforts have been made to educate all personnel in the Defense Materiel Administration (FMV), the Navy, and the defense industry. The hardware example of the Smyge also has been helpful in the process of education and acceptance of all the separate demands that come along with a total stealth concept.

It is the ability to control the signature wall that gives the real advantages of signature control at sea. For instance, if the commanding officer (CO) wants his ship to be seen clearly on radar in a power projection situation, it is easy to use a radar reflector on an erectable mast. It is just as easy, and takes only seconds, to hide this reflector should a serious threat emerge. Similar tactics can be applied in most of the other signature areas, thus offering the CO a wide variety of operating profiles.

Ship Characteristics

The corvette Visby crew will number 41: 21 officers and 20 conscripts. In addition, the ship will be able to accommodate a very small seagoing staff. The systems on board are designed so that all vital systems can be operated using only half of the crew, thus giving good endurance.

The Visby's length overall is 72 meters and the full displacement is approximately 600 tons. The low weight reflects the use of a sandwich of carbon fiber reinforced plastic in the construction of the hull. The different parts of the hull are built from flat panels manufactured with a vacuum injection process to reduce weight even more and ensure a high fiber content and laminate quality. This process, which has been developed by FMV together with Kockums Naval Systems and the Royal Institute of Technology (KTH) in Stockholm, offers something new and unique in shipbuilding. In addition to the low weight, the chosen material has high strength, good shock resistance quality, low magnetic signature, and the desired quality in regard to radar cross section.

The propulsion system consists of a combined diesel or gas turbine (CODOG) installation with two diesels for low speed (under 15 knots) and four gas turbines for high speed (35+ knots). The engines are connected via two gearboxes to two waterjet propulsors. The selection of the low-speed machinery and the waterjets have been made to offer excellent maneuverability during mine countermeasure operations as well as good endurance and very silent operational modes in low speed. The selection of the high-speed machinery uses modern gas turbine technology to offer a wide range of speeds with relatively good fuel economy while at the same time offering a very low weight.

The Visby class will be equipped with wire-guided 400-mm (16-inch) antisubmarine warfare torpedoes with active/ passive homing devices and the newest 127 mm (5-inch) ASW multiple rocket system now under development by Saab Dynamics. An expendable remotely operated vehicle (ROV-E), used primarily for mine destruction, will permit attacks against submarines lying quietly on the bottom. The sonar system is designed to be able to detect, localize, classify, and provide real-time target data to the weapons both at sea as well as in an archipelago and in shallow waters. The system consists of a passive towed array sonar (TAS) for use in open waters, an active/passive variable depth sonar (VDS) for coastal waters and archipelagos, sonobuoy systems, and a hull-mounted sonar for close-in classification. The system is the result of the major effort in ASW undertaken by the Swedish Navy since the late 1980s. Indeed, the Swedish Navy's ASW experience in the complex shallow, brownwater environment has given the service a capability sought after by many navies today.

The MCM system is a development of the systems that are used today on the Swedish Landsort -class MCM-vessels. The Landsorts recently have demonstrated their capability in several sharp MCM operations in the Baltic states. The experiences from these operations have, together with the development of more intelligent and sophisticated mines, led to the development of the systems and tactics that will be used on the Visby class. One example of this is that mines in the future must be handled at greater ranges than today, i.e., outside the range at which the intelligent sensors on future mines can detect any of a ship's signatures. The Visby's MCM system thus consists of a combination of stealth and of sensors and weapons. One ROV-S (S for search) equipped with a high-resolution minehunting sonar and a television camera operates in front of and on the side of the ship's track for detection and classification. A number of ROV-Es (E for expendable) will then be used for identification and destruction of found threat objects. The hull-mounted sonar also will have mine-hunting capabilities.

As an alternate payload, the corvette can be fitted with eight RBS-15 Mark II surface-to-surface missile launchers (two four-tube mountings) for use against ships. These missiles have an effective range exceeding 80 kilometers (50 miles) and are a improved version of the Mark Is that the Swedish Navy operates today.

The Visby's CETRIS' command, control, communication, computers, intelligence and interoperability (C4I2) is a real-time, modular, open-architecture system. This enables the Swedish Navy to integrate coming technologies and weapon systems without fundamental and expensive changes to the C4I2 system. FMV's goal has been to integrate as many as possible of the ships systems and sensors to the CETRIS' system, thus securing a high effectiveness. Furthermore, the system offers very good command capability in joint as well as in combined environments.

The Visby's air-defense system (ADS) automatically and simultaneously calculates and performs hard-kill as well as soft-kill engagements. A system with such capabilities is already in operation in the Swedish Navy on the Goteborg class corvettes and has proved reliable. The development on the Visby goes a step farther. This advance is possible mainly because of the ship's low signature levels that offer the option to use passive parts of the air-defense system to a much higher extent than on a conventional ship. The active part of the system consists of one Bofors 57-mm multipurpose gun. The gun turret is designed as an integrated part of the hull structure and blocked in stealth position until the moment of target engagement. (Space also has been reserved on the Visby for a later outfitting with an air-defense missile system.) The passive part of the system consists of various electronic countermeasures and chaff/flare systems. The system automatically coordinates the active and passive parts, while at the same time it controls the ship's maneuver to obtain maximum protection and effect.

The Swedish Model

The Visby project is led by FMV, an autonomous state authority, which acts like a supplier of defense materiel to the Swedish armed forces. FMV's role is to add value into the materiel process for a system "from cradle to grave." FMV's role changes throughout the various life phases of a system. During acquisition, the task is to provide expertise so that the operational, tactical, technical, and economical demands that are set by the armed forces can be broken down into technical specifications as well as optimized against each other. Afterward, FMV also has the responsibility to acquire the overall system from one or several contractors. The experience from this method is that it offers a very cost-effective way to do business. The Visby project is a fixed-price contract (design-to-cost) and the overall budget approved at the beginning of the project has been met in all aspects. The total contract price in today's money is approximately $500 million (U.S. dollars) for all four ships with subsystems and most weapons.

In this process FMV works closely in cooperation with the Armed Forces Headquarters as well as with numerous Navy representatives on all levels. The latest experiences from personnel from ships of the line are taken into great consideration and affect the project. It is also natural for officers with technical degrees to work for a number of years at FMV, also adding to FMV's competence. In the Visby project four of the leading officers at FMV were very involved with the Smyge project 5-8 years ago and thus provided hands-on experience of stealth ship technology.

FMV also cooperates closely with the national and international defense industry, laboratories, and universities. Special mention should here be given to the long tradition of Swedish naval shipbuilding at Kockums Naval Systems (former Karlskrona shipyard). In many cases, such as in the development of hull materials, this cooperation has been an effective way to reach world-leading and non-expensive solutions in short time frames.

FMV's role together with the armed forces and the defense industry (including the laboratories and universities) is perhaps the key to why the Visby corvettes now are being built in Sweden.


However sophisticated the corvettes seem in the production phase, potential for revolution lies ahead when the ships become operational within the Navy. For the Swedish Navy to succeed in that revolution, and make optimum use of the corvette's full potential, a number of other changes are necessary.

Multimission capability in combination with ever-increasing complexity in shipboard systems means that special consideration must be devoted to training the crew. The introduction of the Visby class will be paralleled by the introduction of high-quality simulation training on board as well as in shore-based establishments. Careful planning of live exercises at sea will be emphasized. Officers' tours on the ships probably will be lengthened to give them time to learn to exploit fully the ships' capabilities. Today, two years on each job in the norm; it is likely that this time will be extended to at least three or even four years.

In Sweden, naval doctrine today builds on a task force concept. While the new corvettes will fit nicely into that concept, they will offer something new. Multimission in combination with stealth will make possible an operational profile similar to that that used by submarines. Like submarines, Visbys will be able to act more independently than previous surface ships. Thus, during a part of an operational scenario, the ship has the ability to cope with several tactical situations without extensive help from other units. This will offer tactical and operational degrees of freedom for commanding officers on different levels.

The built-in capability to operate in international operations with NATO/Partnership for Peace (PFP) countries also means that the Swedish government will be provided with modern ships to help in the execution of its internationally related security strategy. The ships' multimission capability in combination with their automated air-defense system offers something quite distinctive in the littoral environment. It will be the Swedish Navy's task to educate others, both in the Swedish political establishment and in other NATO/PFP countries, about these capabilities.

A revolution also needs a number of dedicated revolutionaries to succeed. Accordingly, a trials unit consisting of handpicked officers has been formed to add to FMV's capabilities and to prepare for the introduction of the ships. Building on the numerous simulations and calculations on the effect of stealth, it is now the trials unit's job to make sure that all the promising capabilities and potential that the Visby has shown are converted into reality. This calls for new and developed tactics and new operational concepts. The trials unit therefore will take the lead to test these ideas, both in simulations, war games, and in full scale sea trials. The officers in the trials unit also have the challenge to educate the rest of the Navy and the other armed forces about the ships' capabilities and the way they can best be employed in various operations.

The trials unit also faces many new challenges because of the corvettes' closed hull form. They must develop the art of seamanship and solve new and as yet unforeseen problems along the way. The art of seamanship therefore will be just as important in the future as it is today.

All in all, the Swedish Defense Material Administration and the Swedish Navy are proud to lead the way into the 21st century in naval stealth ship technology, in the related tactics, as well as in new forms of seamanship with the Visby -class corvettes.

Captain Engevall is the Deputy Program Manager for the Visby -class stealth corvettes at the Swedish Defense Material Administration (FMV), Stockholm, Sweden. He has a M.Sc. in naval architecture from Chalmers University of Technology, Gothenburg, Sweden.  He graduated from the Naval Command College, U.S. Naval War College, in Newport, Rhode Island, in 1997.  His previous assignments include positions at Sweden’s National Defense College, as Chief Staff Engineer Swedish Fleet Staff, and as Commander Sea Trials Unit Smyge (Sweden’s stealth test ship). Captain Engevall is a member of the Royal Swedish Academy of Naval Sciences, the American Society of Naval Engineers, and the U.S. Naval Institute.



Conferences and Events

Maritime Security Dialogue

Mon, 2016-10-03

You are cordially invited to: Maintaining Maritime Superiority A discussion with Admiral John M. Richardson, USNChief of Naval...

2016 Coast Guard Academy Conference

US Coast Guard Academy

WEST 2017

San Diego Convention Center, San Diego, CA

View All

From the Press

Guest Speaker & Book Signing

Sat, 2016-10-01 - Mon, 2016-11-28

Guest Lecturer & Book Signing

Sun, 2016-10-02

Why Become a Member of the U.S. Naval Institute?

As an independent forum for over 135 years, the Naval Institute has been nurturing creative thinkers who responsibly raise their voices on matters relating to national defense.

Become a Member Renew Membership