Monthly Archives: January 2020

Visby class corvette

The Visby Class of stealth corvettes were built for the Swedish Navy by the Swedish company Kockums (a subsidiary of ThyssenKrupp Marine Systems of Germany).

Construction began in 1996 at Kockums’ Kalrskrona yard. The lead ship of the class, Visby (K31), was launched in June 2000 and was delivered to the FMV (the Swedish Defence Materiel Administration) in June 2002 for fitting with weapons and combat systems. The second, HMS Helsingborg (K32), was launched in June 2003 and delivered in April 2006. Harnosand (K33) was launched in December 2004. HMS Visby and Harnosand were officially delivered to the FMV in June 2006.


Visby (K31) – WarshipPorn @reddit

The other hulls are: Nykoping (K34), launched in August 2005 and delivered in September 2006, and Karlstad (K35), launched in August 2006.

Two corvettes, HMS Helsingborg and Harnosand, were delivered to the Swedish Navy in December 2009. The Swedish Navy has cancelled an option on a sixth vessel (Uddevalla K36).

The first four Visby corvettes for the Swedish Navy are for mine countermeasures (MCM) and anti-submarine warfare (ASW). The last vessel will be primarily for the attack and anti-surface warfare role.

Karlstad (K35) and Nykoping (K34) – prahatravel @flicker

A helicopter, such as the AgustaWestland A109M selected by Sweden, can land, take off, and refuel on the upper deck.


The design of the Visby aims to minimise the optical and infrared signature, above water acoustic and hydroacoustic signature, underwater electrical potential and magnetic signature, pressure signature, radar cross section and actively emitted signals.


The picture is a compilation of several drawings, what FMV calls General Arrangements. It shows the location of most equipment and the different types of space are color-coded according to their function. Performance for most machines is also included and various types of equipment are also color coded. Note that the space marked ELA 3 next to the battle line indicates the computer hall. The space RAH is the radio cabin, which may be called the ship’s most secret, where the cryptos are stored. The space of the signal bridge deck sounds nice, but this is where you put the heavy ball guns. Also note that the flagpole is not stealth and will be taken into sharp position. Upload this image separately so you can have it as a reference. Source translated by google

A stealth corvette of the YS 2000 design has a detection range of 13km in rough seas and 22km in calm sea without jamming. In a jammed environment, the Visby would be detected at a range of 8km in rough sea and 11km in calm sea.


The hull material is a sandwich construction comprising a PVC core with a carbon fibre and vinyl laminate. The material provides high strength and rigidity, low weight, good shock resistance, low radar and magnetic signature.

K33 HMS Haernosand – Arne Lütkenhorst @flickr

Signature reduction measures

The most obvious part here are the radar cross section reduction measures. A lot of thought have gone into this, below you see the back of the 57 mm cannon which has had its shape adapted.

Many less noticeable aspects include the coating of the bridge windows with indium tin oxide and gold which prevents radar returns from objects inside. Hatches and vents are also adapted with things such as a honey comb grid which also prevents returns, while radar absorbent materials have also been added in selected areas. The antennas are retractable into the hull as are the floodlight and fog horn, and even the navigation lights have been adapted to not stand out. They are fitted with quadruple redundant LED lights to avoid giving off a heat signature which brings us to the next point.

The aspect of thermal signature


Great lengths have been taken to prevent the ship from being detectable with thermal imaging. As the largest heat source are the engines and in particularly the gas turbines, the exhaust is water injected which brings down the temperature to just above room temperature before the exhaust exits the hull.


This picture shows the air intake for the low speed diesel machinery, here you can see the radar reflecting honeycomb material (Ra) which the air passes through. After that it enters the filter and then on to the diesels. In case the sea waters splashes the honey comb and causes icing during the winter a pneumatic hatch below (Ö) automatically opens to allow air to continue flowing, this is however not stealthy.

The paint of the ship’s hull has also been specifically developed to reduce the IR signature.

The hull structure

It is in basically a composite design of carbon fibre reinforced plastic (CFRP) with an exterior carbon fibre laminate, a middle section of divinycell – which is a light weight material – and more carbon fibre on the inside. This material reduces the hull weight significantly, down to about 50% of an equivalent steel hull.


The carbon fibre conducts electricity which is both good and bad. Good in that it provides shielding of radio signals and bad in that it creates galvanic corrosion. Most of the hull is built with vacuum injected laminate and the rest is hand fitted. The ships were built in three sections which were then joined together. The hull has been designed so as to be able to negotiate a mine detonation under the keel without snapping. To aid in damage control and general operations stress load sensors are fitted throughout the hull, these allow the crew to assess the hulls integrity and make decisions based on it. Source

Command and control

The vessel’s CETRIS C3 (command, control and communications) system consists of the Saab Systems 9LV mk3E combat management system, the MAST decision support aid and the integrated communications system.

The 9LV mk3 is based on open system architecture and uses the Windows NT operating system.


The SaabTech CEROS 200 radar and optronic fire control system has been ordered for the Visby and will be fully integrated into the combat management system.



CEROS 200 Fire Control Radar

Saab’s CEROS (Celsius Tech Radar and Optronic Site) 200 is a ship-based search and tracking radar system capable of engaging targets above supersonic speeds. The CEROS employs a variety of sensors such as infrared, electrooptical, televisual, and laser. According to a publication by Saab, CEROS is able to detect sea-skimming missiles via its patented CHASE algorithm. Saab explains that this algorithm mitigates the effect of multiparty wave interference, which is when signals are sent to a receiver by multiple sources. For example, a missile may emit a signal to a receiver, which then sends it to command and control at the same time that a signal directly from the missile reaches command and control. In this instant, the two signals would arrive with different phase shifts — think: a sine wave placed in front of another, so that there’s no exact overlap. This can result in the ghosting effect sometimes observed on television in which images appear to have a shadow duplicate on them. Source

General data:
Type: Radar Altitude Max: 30480 m
Range Max: 46.3 km Altitude Min: 0 m
Range Min: 0.2 km Generation: Early 1990s
Properties: Moving Target Indicator (MTI), Pulse Doppler Radar (Full LDSD Capability)
Sensors / EW:
CEROS 200 Tracker [9LV Mk3E CETRIS] – Radar
Role: Radar, FCR, Weapon Director
Max Range: 46.3 km

K33 HMS Haernosand –

The communications system has a high-capacity digital communications switch, developed by Danish company Maersk Data Defence (formerly Infocom) together with Karlskrona, which interconnects the voice and data communications channels. The system provides internal communications or open conference lines and access to external communications with various radio links and land-based networks.


HMS Visby

Visby vessels were not initially fitted with an air defence missile system, but could later be equipped with one. It has been reported that the Swedish government has selected the Umkhonto surface-to-air missile system, produced by Denel of South Africa. Umkhonto has infrared guidance, range of 12km and ceiling of 10,000m. The system is capable of engaging up to eight targets.

The corvettes are equipped with eight Saab Bofors Dynamics RBS 15 mk2 anti-ship missiles. The RBS 15 mk2 uses active Ku-band radar homing and has a range of more than 200km. The missile has a high subsonic speed, Mach 0.9, and is armed with a 200kg warhead. The missiles will be installed below deck and be fired through special hatches to maintain the vessel’s stealth. The missiles’ exhaust plumes will be managed in separate canals.

RBS 15 mk2 anti-ship missiles



The RBS15 is a long range, sea-skimming, fire and forget, anti-ship missile for use from aircraft, ships and ground vehicles. It features a tactical flexibility trajectory with a large number of waypoints and altitudes to hide the launching location increasing the survivability of the launching platform. It is suitable for blue sea operations and littoral warfare. The missile has two lateral boosters for extended range, without the booster the RBS15 only weighs 630 kg. The RBS15 guidance system consists of a GPS/INS and radar altimeter navigation system and a terminal phase active radar seeker. The RBS15 missiles are countermeasures resistant and several of them can be programmed to reach the target area simultaneously from different directions to better penetrate the ship’s air defenses. Source

K32 HMS Helsingborg –

Anti-submarine warfare

The Visby is equipped with a suite of ASW 127mm rocket-powered grenade launchers, depth charges and torpedoes. There are three fixed 400mm torpedo tubes for Saab Underwater Systems Tp 45 anti-submarine homing torpedoes.

Tp 45 anti-submarine homing torpedoes


Source: Jimmie Adamsson/Försvarsmakten via

The Torped 45 is a lightweight torpedo intended for ASW and surface targets, providing multiple-target active/passive homing combined with wire guidance. It is designed and manufactured by Saab Dynamics. It was designed for the Swedish Navy, based on the experience gathered from the well proven 43-series of torpedoes.

Torpedo 45 can be launched from a variety of platforms including stationary, surface vessels, submarines and helicopters. It was specifically designed to operate against shallow-water targets and surface vessels. It is controlled using wire guidance and has a hydro-acoustic homing system for the final phase. The torpedo has features that are unique for lightweight torpedoes.

  • It combines wire guidance and homing control
  • It can be launched from submarines, surface vessels and helicopters
  • It can be wire-guided from a flying or hovering helicopter (no parachute necessary)
  • Its warhead has a main charge large enough to take out any conventional submarine or seriously damage light surface vessels

In exercise torpedo launches, the warhead is replaced by an exercise head carrying identical homing equipment. Instead of explosives, the exercise head has a tape recorder for logging a number of torpedo functions, communication with fire-control and hit indications. After each run, the recordings are analysed and torpedo and fire-control functions are checked.

The Torped 45 is set to be replaced by the newer Torped 47 in Swedish Service fully 2024. Source

General data:
Type: Torpedo Weight: 320.0 kg
Length: 2.9 m Span: 0.4 m
Diameter: 0.4 Generation: None
Properties: Search Pattern, Bearing-Only Launch (BOL), Re-Attack Capability
Targets: Submarine
Sensors / EW:
Torpedo Seeker – (Tp 45 Passive Anti-Submarine, Small-Caliber) Hull Sonar, Passive-Only
Torpedo Seeker, Passive-Only
Max Range: 1.9 km
Tp 451 – (1997, Tp 43X2) Torpedo
Subsurface Max: 7.4 km.





The Visby is equipped with a Bofors 57mm 70 SAK mkIII general purpose gun. The gun has a fully automatic loading system containing 120 rounds of ready-to-fire ammunition. The gun fires up to 220 rounds a minute to a maximum range of 17,000m.

Bofors 57mm 70 SAK mkIII general purpose gun

K32 HMS Helsingborg – MilitaryPorn

Work on these weapons began in 1962 based largely upon experience gained with the Bofors 57 mm/60. Compared with that weapon, the major improvements of the Mark 1 were a higher rate of fire, the use of new munitions including an improved proximity fuse, water cooling for the gun tubes and a new electro-hydraulic system for rapid training and elevation. The Mark 1 was exported to Malaysia and (the former) Yugoslavia.

K33 HMS Haernosand – Arne Lütkenhorst @flickr

The Mark 2 was a lighter weight mounting and used a new servo system that reduced aiming errors and damping time. The gun barrel for this mounting used a special monobloc steel that eliminated the water jacket Bofors claimed that this gun was dual-purpose in that it was accurate and agile enough to destroy sea-skimmers and that it could put more explosives into a surface target in thirty seconds than any gun smaller than 10 cm (3.9″). In reviewing this weapon, the US Navy concluded that it was heavy when compared to the OTO-Melara 35 mm and 76 mm weapons. About 25 Mark 2 guns were manufactured.

The Mark 3 is the latest version. This mounting uses the same ammunition as the Mark 2 but also can fire “smart” ammunition. The Mark 3 is offered with an optional low radar profile (RCS) mounting which hides the gun barrel when not in use. It is claimed that the Mark 3 has a mean time to repair of 30 minutes and can be installed on ships as small as 150 tons (152 mt). This mounting uses a small radar mounted on the gun barrel to measure muzzle velocity for fire control purposes. The dual-hoist system allows instant switching between ammunition types, but rounds must be removed manually in case of misfire. This mounting can open fire at 45 degrees training and 35 degrees elevation from the stand-by condition in 2.2 seconds. The mounting is normally remotely controlled, but can be used in a gyro-stabilized local control mode.

Bofors was taken over by United Defense, which in turn has been taken over by BAE Systems. Source

Mine countermeasures (MCM)

The Visby carries Saab Bofors Underwater system ROVs (remotely operated vehicles) for mine hunting and the Atlas Elektronik Seafox ROV for mine disposal. The minehunting ROVs are a development of the Double Eagle mkIII.

Atlas Elektronik Seafox ROV


Wikimedia Commons

This fibre-optic guided, one shot mine disposal vehicle is used for semi-autonomous disposal of naval mines and other ordnance found at sea. It is able to automatically relocate previously acquired positions of underwater objects within minutes with the integrated homing sonar.After relocating, these objects can be identified using the onboard CCTV camera and destroyed by the use of a built-in, large caliber shaped charge. The one-way concept significantly reduces the disposal time and extends the operational envelope.


The system has been fully qualified for military purposes and has been introduced in large numbers into various navies. It is deployable from a wide range of carrier platforms, including dedicated MCM vessels, surface combatants, craft of opportunity, rubber boats and helicopters.

The SeaFox system is a mine disposal system based on the most advanced concept using the Expendable Mine Disposal Vehicle principle (EMDV).

Small, unmanned underwater drones are used for direct disposal of historical and most modern mine types; identical, reusable vehicles (without charge) are used for inspection, identification and training purposes.

The system is effective against long and short tethered mines, proud ground mines and floating mines.

The SeaFox system mainly comprises a console, a launcher and the SeaFox vehicles. The system can be delivered as a stand-alone or a fully integrated version.


In case of stand-alone the console contains all electronics, software, displays and operating elements to guide the vehicle automatically or manually towards the target and to relocate, identify and destroy it. In the fully integrated version, a Multi Function Console or any existing console can be used.

The two different vehicles ensure quick disposal of mines during operation with the combat vehicle (SeaFox C) as well as cost-saving identification with the reusable identification version (SeaFox I). Source

The Visby corvettes are fitted with the Hydra multi sonar suite from General Dynamics Canada (formerly Computing Devices Canada), which integrates data from a Hydroscience Technologies passive towed array sonar, C-Tech CVDS-26 dual-frequency active Variable Depth Sonar (VDS), C-Tech CHMS-90 hull-mounted sonar and data from the ROVs.

Hydroscience Technologies passive towed array sonar

The Towed Array Sonar has a length of 1,300 meters and has microphones set at one meter intervals. The Visby Class have an active and a passive component and can be lowered to a depth of 100 meters. It is seen here in its stored position located between and above the water jets. Source

General data:
Type: TASS, Passive-Only Towed Array Sonar System Altitude Max: 0 m
Range Max: 27.8 km Altitude Min: 0 m
Range Min: 0 km Generation: Early 2000s
Sensors / EW:
Hydra TASS – (Visby) TASS, Passive-Only Towed Array Sonar System
Role: TASS, Passive-Only Thin Line Towed Array Sonar System
Max Range: 27.8 km


C-Tech CVDS-26 dual-frequency active Variable Depth Sonar (VDS)

General data:
Type: VDS, Active/Passive Sonar Altitude Max: 0 m
Range Max: 27.8 km Altitude Min: 0 m
Range Min: 0 km Generation: Early 2000s
Sensors / EW:
CVDS-26 Hydra – (Visby) VDS, Active/Passive Sonar
Role: VDS, Active/Passive Variable Depth Sonar
Max Range: 27.8 km


C-Tech CHMS-90 hull-mounted sonar

General data:
Type: Hull Sonar, Active-Only Altitude Max: 0 m
Range Max: 1.1 km Altitude Min: 0 m
Range Min: 0 km Generation: Early 2000s
Properties: Classification [Class Info] / Brilliant Weapon [Automatic Target Aquisition], Shallow Water Capable (Full) [Classification Flag Required]
Sensors / EW:
CHMS-90 Hydra – (Visby) Hull Sonar, Active-Only
Role: Hull Sonar, Active-Only Shallow Water High-Definition Mine & Obstacle Avoidance
Max Range: 1.1 km



David Oliver

Saab Microwave Systems (formerly Ericsson) Sea Giraffe AMB 3D C-band multi-role radar provides air and surface surveillance and tracking and target indication to weapon systems. It features 3D agile multi-beam technology and can handle multiple threats up to 20,000m (65,000ft) at elevations up to 70°.

Sea Giraffe AMB 3D C-band multi-role radar


Today the Sea Giraffe AMB has the designation AN/SPS 77 V(1) for the US Navy’s Littoral Combat Ship, LCS 2/4 and AN/SPS 77 V(2) for LCS 6 and higher.

Sea Giraffe AMB comprises the following main hardware units:

  • Antenna Unit (AU)
  • Transmitter Unit (TRU)
  • Signal and Data Unit (SDU)
  • Power Distribution System (PDS)

The following extended capabilities for the Sea Giraffe AMB baseline product configuration are available:

  • Stealth Radome
  • 360˚ mortar/rocket detection and alert (C-RAM)
  • Identification Friend or Foe (IFF) interrogator antenna
  • IFF interrogator
  • Improved detection range and redundancy with an additional transmitter unit

The stealth radome is built with Frequency Selective Surfaces (FSS) to minimise the Radar Cross Section (RCS) and infrared signature of the above-deck parts of the Sea Giraffe AMB. The radome is capable of carrying equipment on the top, for example an ESM, ELINT and/or a COMINT. The counter rocket, artillery and mortar alert function detects, tracks and classifies very small ballistic objects in severe clutter. The point of impact, the ballistic trajectory as well as the impact position are calculated. A warning signal of impact position is given well in advance, allowing the ship to perform an evasive manoeuvre in order to avoid being hit.



Radar type Stacked beam 3D radar
Antenna type 3D phased array, digital beam forming
Frequency C (G/H)-band
Elevation coverage > 70 degrees
Rotation rate 60 RPM
Instrumented range 180 km


ECCM (electronic counter countermeasures) capabilities include ultra-low antenna sidelobes and both frequency and code agility. The antenna has a rotation rate of 30rpm for surveillance and 60rpm for air defence.

There is also an I-band surface search and I/J-band fire control radar.


The CS-3701 tactical radar surveillance system (TRSS) from EDO Reconnaissance & Surveillance Systems provides electronic support measures (ESM) and radar warning receiver (RWR) functions.

CS-3701 tactical radar surveillance system (TRSS)

The ES-3701S is a high-performance radar electronic support measures (ESM) system for surface naval applications. The ES-3701S ESM system provides complete radio frequency (RF) coverage with direction finding (DF) from communication through radar bands. The ES-3701S provides situation awareness, targeting, self-protection and surveillance. The system has been interfaced to many combat management systems (CMS) and uses a Windows graphical interface, which can also be run on multifunction consoles.

Precision Radar ESM Capabilities

  • High probability of intercept for instantaneous emitter detection
  • High sensitivity for long-range detection
  • Accurate angle of arrival (AOA) on every pulse
  • Wideband, narrowband and low-band subsystems for comprehensive signal exploitation using advanced sapience emitter processing algorithms
  • High-sensitivity frequency-modulated continuous wave (FMCW) radar detection and identification (-95dBm)
< 1 second reaction time
Processes 1 MPPS signal environment
20,000 emitter mode library capacity


General data:
Type: ESM Altitude Max: 0 m
Range Max: 926 km Altitude Min: 0 m
Range Min: 0 km Generation: Early 2000s
Sensors / EW:
ES-3701 Seawatch – ESM
Role: ELINT w/ OTH Targeting
Max Range: 926 km


Visby Class vessels are equipped with the MASS (multi-ammunition softkill) decoy system from Rheinmetall Waffe Munition (formerly Buck Neue Technologien) of Germany.

MASS can launch up to 32 omni-spectral projectiles in a time-staggered configuration against anti-ship missiles and guided projectiles. The MASS decoy covers radar, infrared, electro-optic, laser and ultraviolet wavebands.

MASS (multi-ammunition softkill) decoy system


MASS has been designed to provide multi-spectral protection against guided weapons in all relevant wavelengths of the electromagnetic spectrum (including radar, infrared and electro- optical). Suitable for installation on a wide range of platforms, it can be integrated into an existing command and weapon control system, or operated as a standalone system.

Typically MASS consists of between one and six trainable launchers, each able to fire 32 standard Omni-Trap munitions. Each launcher comes with a control unit and a data interface (Ethernet/ RS422 or other standard interface).

At IDEX the company is showcasing two new options: MASS_OCR with an off-board corner reflector (OCR) payload; and the new standalone MASS Stand Alone with Sensor Suite for smaller units.

The MASS_OCR introduces a new corner reflector countermeasures payload, designed to produce a ship-like radar response, which can be used in either the distraction or seduction modes. Each launcher unit can be configured with two OCR rockets programmed to deploy the corner reflector to a range of between 35m and 850m. The reflector payload itself is suspended beneath a parachute, sustaining the effect for over 60 seconds.

With the MASS Stand Alone with Sensor Suite, Rheinmetall has engineered a self-contained system with its own control unit, power supply and sensor suite (a radar warner and a laser warning system) and typically one or two MASS decoy launchers. Source



The Visby is equipped with a combined diesel and gas (CODAG) turbine arrangement. Four TF 50 A gas turbines from Honeywell and two MTU 16V 2000 N90 diesel motors are connected to two gearboxes which run two Kamewa waterjet propulsors.

K33 HMS Haernosand – Arne Lütkenhorst @flickr

4 x TF 50 A gas turbines

Vericor’s TF50B marine gas turbine is an aeroderivative that powers numerous ships, for example the Visby-class corvettes of the Swedish Navy or mega yachts, such as the Pershing 115. For commercial applications, Vericor has developed the new Integrated Turbine Control Panel which combines the control functions for gas turbine and reduction gearbox, the cockpit interface and the local operating panel into one single unit.


  • Compact, lightweight
  • High operational readiness
  • Operates on LNG, natural gas and / or marine diesel fuel
  • Smallest installed volume / lowest installed weight
  • Modular engine design reduces maintenance cost
  • Simplified installation with cold end drive and cantilever mount
  • Precise digital engine control and monitoring
  • No warm up required / start capability down to -50°C
  • Low vibration and ultra low emission levels
  • Single, twin and tri-pack configurations

The high-speed machinery consists of two pairs of gas turbines (Vericor TF50A, Tr and Tr2) of 4.2 MW each. The exhaust gases blow out through the heat insulated exhaust pipe (Avg) and further back into the vessel. The turbines draw in 30 m³ of air (In) per second. Therefore, they have their own air intakes with radar grilles on the ship’s side. Source translated by google

Technical Data

Power (kW)* 3,800 – 4,200
Weight (lbs/kg)** 1,445/657
Length flange to flange (in/mm) 52/1,321
Height (in/mm) 41/1,046
Width (in/mm) 35/889
Output speed (rpm) 16,000

*Average engine performance at ISO conditions 15 deg. C, no inlet, exhaust or gear losses

**Weight is for gas turbine complete with lube, fuel and control system


2 x MTU 16V 2000 N90 diesel motors


The motors provide a maximum speed of 15kt for long duration and 35kt for short duration. The ship has rudders and bow thrusters for harbour manoeuvring.


Here, the water jet units (VJ) are stowed in a stop position, angled 30 degrees inwards. Each unit weighs 10 tonnes and is made of non-magnetic bronze. What is not done in bronze is instead made in composite material or titanium. The pump housing is specially developed by KaMeWa to be as quiet as possible.

Between the units is a pair of shiny cylinders in stainless (Int). These are the pistons for the interceptor blades. These can be described as two long razor blades that are flush with the transom, approximately 150 mm high and 20 mm thick, and serve as a trim plane. But instead of needing a big blade in the stern, you just put down a small knife. The blades are actively controlled by a gyro system that compensates for rolling, stomping and side winds. The system depresses the blade on the ship’s side that goes into the water, so it is pressed again. The blades can operate at 35 knots and improve both comfort and weapon performance.

The exhaust pipes from the high-speed engines are not visible, because they come out under the “shelf” and point straight down. Between the exhaust pipes is the trailing headphone cover (F-VDS). The big hatch at the top of the picture is the mine hatch, from which you drop mines and sink bombs. The sneak-fit stern lights, the hatch for the snare sonar TAS and a pair of belt throwers are not visible in the picture. Source translated by google

K31 HSwMS Visby – corax71 (flickr)

Technical specifications

Overall length 73 m
Beam 10.4 m
Displacement 640 tonnes (fully equipped)
Draught 2.4 m
Crew 43
Hull material Sandwich construction carbon fibre reinforced plastic (CFRP)
High-speed machinery 4 gas turbines, total rating 16 000 kW
Low-speed machinery 2 diesel engines, total rating 2600 kW
Propulsion 2 waterjet propulsors
Speed >35 knots

Technical data source

Main material source

Images are from public domain unless otherwise stated

Main image K34 HSwMS Nyköping – Tyler Rogoway