New Swedish Frigate

ComNavOps has long considered the Swedish Visby class corvette as the gold standard of modern, total stealth warship design (not perfect ... just the best out there).  That makes the conceptual design for the next Swedish frigate, a larger vessel than the Visby, seemingly obvious:  simply upsize the Visby and add a few more weapons.  However, that seems not to be the case.  The candidates for the next Swedish frigate appear to be the existing (parent??) designs listed below:
 

• Saab/Babcock - Arrowhead 120 (variant of the Arrowhead 140)
• Naval Group (France) - FDI frigate
• Navantia (Spain) - Alfa 4000 light frigate

 
As a quick reminder, Visby is 238 ft and 840 tons.  For comparison, the Arrowhead 120 is 406 ft and 4,650 tons.
 
None of the candidates exhibit anything approaching the maximum stealth and total signature reduction the modern naval battlefield requires and all would seem to be a significant step back from the Visby in that regard.  Honestly, the parallels between this and the US Navy’s failed Constellation program which attempted to build a “new”, 20+ year old, already obsolete frigate from a parent design, are eerie.
 
Sweden is looking to acquire four frigates from one of the companies listed above.  The contract for four ships is estimated to be between $4.5B -$6.7B(USD) which would be $1.1B - $1.7B(USD) per ship and, of course, no estimate ever comes in on budget so the real cost would likely be pushing $2B or more which seems excessive for relatively simple, dated frigates.
 
I assumed Sweden would simply scale up the Visby design for frigtes/destroyers.  That would be eminently logical and, indeed, that was the original idea for the Visby Generation 2 design.
 

Initially in 2021, FMV [Swedish Defence Materiel Administration] awarded Saab Kockums a contract for the product definition phase of the Visby Generation 2 corvettes, a new class based on the existing Visby-class stealth vessels … [1]
 
However, the program was canceled in 2023 amid Russia’s 2022 invasion of Ukraine and Sweden’s push toward NATO membership (finalized in 2024), leading to Saab teaming up with Babcock for a new, larger design.[1]

Somehow, in moving from the world’s stealthiest corvette to a “new” dated frigate, Sweden lost sight of what’s important for survival and combat-effectiveness on the modern naval battlefield.  Did some US admirals join the Swedish navy?
 

Arrowhead 120

I fully support the idea of a larger ship than the Visby but why go for a less capable and less survivable one?  Surely, the Visby could be scaled up from a corvette to a frigate without violating any “laws” of shipbuilding.
 
I guess it’s not just the US Navy that engages in perplexing behavior.
 
 
 
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[1]Breaking Defense website, “Saab, Babcock bank on Arrowhead 120 design for Sweden’s next frigate”, Jonas Olsson, 13-Feb-2026,
https://breakingdefense.com/2026/02/saab-babcock-bank-on-arrowhead-120-design-for-swedens-next-frigate/

Visby As The Model

ComNavOps has frequently cited the Swedish corvette Visby as the model for future WARship designs based on the extreme (compared to current standards) radar stealth of the ship.  Radar stealth, while not the be all and end all of WARship design, is, without a doubt, the minimum price of admission to the modern naval battlefield.  Stealth, alone, won’t guarantee success or survival but the absence of stealth will guarantee failure and destruction.  Visby is the only existing, functional high stealth WARship that I’m aware of.  Yes, there are other experimental prototypes that claim high stealth (Sea Shadow, for example) but they aren’t functional WARships – they’re experiments that emphasize one attribute not the entire WARship package.
 
What does it mean to call for Visby as the model for future US Navy WARship design?  Well, it doesn’t mean to make an exact copy and just add a hundred feet of length – though that would likely produce a much better ship than what we have now!  What it means is to take the conceptual attributes of the Visby and incorporate them into a clean sheet design.  However, even that is not the end of it.  Visby, while decently (not great) equipped and armed for a corvette, lacks many attributes that a high end WARship will need for the future naval battlefield.  So, what should we take from Visby and what do we need to add? 

 

Visby

Stealth – Visby’s radar stealth is due in large measure to its angular, uninterrupted shape with very few protuberances.  Compare Visby’s look to our latest Burkes and the Constellation and you’ll instantly see just how obsolete the Burkes and Constellations are in this regard.  They’re jokes and will stand out on the battlefield like the radar beacons they are.  Several decades ago, the Burke was notable for its stealth but that time is long since passed.
 
Electromagnetic Stealth – Radar stealth is not enough, by itself.  We need extreme emissions control across the entire spectrum.  Not a single stray electron can be emitted if a ship hopes to survive.  Visby may or may not have this – I suspect not.
 
Acoustic Stealth – This is how you gain a degree of immunity from submarines.  A ship cannot allow any avoidable noise to escape.  Note that this likely means downgrading other attributes such as speed (no giant waterjet trumpets – looking at you, LCS).  I have no idea to what extent, if any, Visby has this.
 
Visual Stealth – This is an ignored aspect and we need to incorporate modern coatings and processes (electrochemically reactive coatings, for example).  Old fashioned camouflage, adapted to disrupt optical seekers, is necessary and we’re not talking about the idiotic, crew-designed camo schemes on the LCS.  Visby does not have this, at all.
 
Infrared Stealth – Modern ships cannot emit a significant infrared signature.  Active cooling systems are mandatory and engine exhaust must be significantly cooled even is this means downgrading performance (underwater exhaust, for example, which creates backpressure and decreases engine performance).  The current nuclear washdown systems, adapted to infrared cooling, would be a good start towards heat signature management.  Non-heat absorbing coatings and materials should be developed.  Visby does not have this.
 
Weapons Density – We’ve talked at length about the extremely sparse weapons density on modern ships and Visby is as guilty of this as anyone.  We need to load the new ship with weapons appropriate for its size and purpose.  To offer one ballpark example, no major WARship should sail without a minimum of 8 close in weapon system (the Burkes have 1 – what a joke).
 
UAV – We’ve talked at length about ships needing to be able to operate many dozens of small, stealthy UAVs for situational awareness.  This means the ship needs a small catapult/launcher of some sort, a recovery mechanism, and storage for many dozens of UAVs.  Visby has no such capacity.
 
Electronic Warfare – Todays EW is a joke.  We need ten times the capacity, antennae, power, and sensitivity of existing SLQ-32/SEWIP systems.  We also need to emphasize offensive/active EW, not just detection and defensive.  Again, this means output power.  Visby does not have this.
 
Optical/Passive Sensors – To emit is to die.  The modern WARship’s sensors must be optical/passive and incorporate automated search/tracking and fire control … in other words, an optical/passive Aegis system.  Visby does not have this.
 
Range of Weapons – The modern trend towards nothing but VLS missiles is idiotic.  Naval warfare demands flexibility which demands a wide range of weapons.  The modern ship needs missiles, of course, but it also needs large caliber guns (appropriate for its size and role), medium caliber guns, and small caliber guns, heavy torpedoes, ASW RBUs, small anti-drone weapons, lasers (because, they’re just around the corner of being ready, right??), etc.  Visby does not have this to an effective degree.
 
 
Conclusion
 
It is obvious from the preceding discussion that Visby is the only logical starting point for modern WARship design but it is not the end point.  It lacks many of the required attributes for a survivable, effective WARship.  Think of the Visby as the USS Monitor - it’s a great first step towards a truly modern WARship but nowhere near the end product of the required development.

The Stealthiest Ship Ever Built

The US military is building its entire force structure around the concept of information which includes data collection, surveillance, networks, etc.  In other words, the military is assuming – or, at least, working towards the goal of – perfect battlefield awareness, believing that will make up for vast, self-inflicted shortcomings in firepower.  Setting the lunacy of that assumption aside, the implication is that the US believes that all will be known and seen on the battlefield.  Accepting that premise for the sake of analysis and discussion, we must also assume that the Chinese will have the same degree of total vision and situational awareness.

 

What, then, does that suggest about the survivability of naval forces?  It’s obvious, isn’t it?  Only the most stealthy platforms will be able to evade detection for any useful time period.  Unfortunately, none of our current naval surface ships come remotely close to that level of stealth.  In order for a ship to survive on the future naval battlefield, it will need to have maximum stealth across the entire electromagnetic spectrum and beyond.  With that in mind, why don’t we have a bit of fun and see if we can come up with a conceptual design for a future ship – it doesn’t matter what type – that is the stealthiest possible given our current level of technology? 

 

Before we go any further, we need to briefly review what stealth is. 

 

While most people associate the term ‘stealth’ with radar signature, the term actually encompasses much more.  The definition of stealth is the ability to evade detection.  That evasion can include measures such as reduced radar signature, reduced infrared signature, reduced acoustic signature, altered visible signature (camouflage), the use of multi-spectral obscurants, decoys (chaff, flares, emitters), electronic warfare, tactics (avenues of approach, use of weather), etc.  It should be noted that some of these do not have to be part of the ‘hiding’ platform’s capabilities but can be provided by other platforms in support of the ‘hider’.  For example, an F-18G Growler electronic warfare aircraft can provide stealth cover for other ships or aircraft by using its EW/jamming capabilities to reduce the likelihood of detection of the ‘hiding’ platforms.

 

Of course, having organic stealth measures helps, too!

 

So, understanding everything that goes into making a platform – a ship, in this case – stealthy, let’s see if we can conceptually design the ultimate stealth surface ship, just for fun.  What would it look like?  What characteristics would it have?  What unique aspects would be incorporated into this design that are not currently common? 

 

For this exercise, we’ll only consider the organic stealth measures and ignore the off-board measures from other platforms.  Thus, we’ll concern ourselves with size, radar signature, acoustic signature, infrared signature, optical visibility, electromagnetic emissions, obscurants, decoys, electronic warfare, and wake suppression.  Some of these factors are pretty obvious so, for the sake of brevity, I won’t belabor them.

 

Size – The most basic – and almost universally ignored – aspect of ship stealth is size.  Simple size.  All else being equal, a smaller ship is harder to detect than a larger ship.  A smaller ship naturally has smaller signatures across the electromagnetic spectrum.  This is a fundamental truth that the Navy has totally ignored as it continues to produce ever larger ships.  The WWII Fletcher class destroyer was 376 ft long versus a Flt IIa Burke class destroyer which is 509 ft long.  A WWII Atlanta class cruiser was 541 ft long versus a Zumwalt class cruiser (the Navy misleadingly calls it a ‘destroyer’) which is 610 ft long.  The Brooke class FFG was 414 ft long which was followed by the larger Perry class FFG which was 453 ft long which was followed by the still larger Constellation class FFG which is 496 ft long.

 

One of the largest drivers of ship size is the Navy’s obsession with helicopters.  The Navy believes that every ship must have a helicopter with its attendant flight deck, hangar, magazines, maintenance shops, additional crew, etc. which make up a third of a ship’s length and superstructure.  No ship should have a helicopter unless it is absolutely required for the execution of its primary mission.  For example, an AAW escort has no need for a helo which instantly reduces the ship’s size by a third – a nice chunk of ‘instant stealth’!

 

Included in size considerations is the superstructure.  Superstructures have grown enormously since the ships of WWII (see, “Ship Superstructures”).  Every square foot of superstructure area and every cubic foot of superstructure volume increases the ship’s various signatures.

 

The obvious conclusion is that our stealthy ship must have the smallest hull size and smallest superstructure possible, consistent with its mission requirements (CONOPS).

 

 

Radar Signature – This is the commonly understood measure of stealth and needs little further discussion other than to note that a truly minimized radar signature requires that there be no protruding objects such as railings, sensor domes, antennae, line handling equipment, platforms and supports, cabling, electrical junction boxes, firefighting plumbing, etc., all of which our current ships have in abundance.  Our conceptual starting point, in this respect, is the Swedish Visby which is nearly as free of protruding items as possible (see, “Ship Stealth and Visby”).

 

Visby - Note the relative lack of protruding objects

Acoustic Signature – Arguably, the most lethal threat to ships is the submarine and the main means of detection that a submarine uses is acoustic sensors.  Our ship must be as quiet as possible.  Every known acoustic suppression method must be used, including isolation and rafting of internal machinery, selection of inherently quiet machinery, Prairie-Masker, vibration dampening, cavitation suppression, etc.  Silence must take priority over speed.  The powertrain and propulsion must be the quietest possible.  We cannot use massive noise beacons like water jets.  I do not have detailed acoustic data about propulsion pods but I suspect they may be a good choice since they eliminate the use of long, large, noisy propeller shafts and combining gear.  I also do not have acoustic data on turbines versus, say, diesel engines.

 

The point is that the propulsion system must be selected for reduced sound rather than maximum power or speed, again, consistent with mission requirements.  This would be a radical departure from current ship design.

 

Infrared Signature - Ideally, our ship should have a temperature identical to the surrounding ambient air and water.  One of the major IR sources is, of course, the hot exhaust from the commonly used turbine engines.  If we can’t find a better choice than turbines, we need to, at least, suppress the heat of the exhaust by discharging the heated air through a water mist or exhausting the air into the water[4] or very near the waterline in a water-cooled discharge.

 

The rest of the hull and superstructure gets hot from internal heat sources and heat absorption from the sun.  The hull and superstructure need a cooling system similar to the Nuclear/Biological/Chemical (NBC) washdown system.  In this case, instead of washing away radioactive particles, the washdown would serve to cool the ship’s skin and reduce the IR signature.

 

Optical Visibility – Many weapons use optical sensing for target identification, terminal guidance, and impact point selection.  We must reduce or alter our optical signature as much as possible by reducing ship and superstructure size and by applying camouflage to break up or alter the ship’s outline.  Interestingly, early WWII Gato submarines had relatively large superstructures which, in combat, were quickly cut down to reduce their visible detectability.  We must follow this example.  The least detectable superstructure is no superstructure.  While that may not be totally achievable, it is the goal we must strive for.  We must ruthlessly eliminate any non-combat compartment in the ship.  This means no ship’s post office, no gym, no crew lounge, no chapel, no lawyer’s office, etc.  This is a ship of war not a cruise ship.  Every non-combat space that can be eliminated allows us to reduce the size of the superstructure.  I guarantee that every sailor will gladly choose survival in combat over a coffee bar or video game lounge.

 

An intriguing area for research is the use of adaptive electrochromic coatings/paint that can alter their color, reflectance, and other properties depending on temperature, light and light angles, and electrical state.  To the best of my limited knowledge, these are not available for field use but they should be aggressively pursued as near term research projects.[3]

 

Electromagnetic Emissions – This is our old friend, EMCON.  This is well understood and, until very recently, totally ignored by the Navy.  I won’t belabor this further other than to emphasize that our conceptual ship cannot have any stray emissions and must be designed to operate without active emissions to the maximum extent possible.  This means emphasizing passive detection and tracking of targets versus active.  To the maximum extent possible, fire control must utilize passive sensing.  Every piece of equipment on the ship must have a verified EMCON mode of operation.  It goes without saying that cell phones, video games, or any other personal electric device must be banned.

 

Obscurants – ‘Smoke’ has been developed that can provide multi-spectral interference (concealment) and can be deployed as any other shipboard decoy canister.

 

Decoys – This is a vastly under-emphasized aspect of stealth.  Not to belabor the obvious but decoys mimic a real target in hopes that an attacking weapon will be fooled into selecting the decoy instead of the real ship.  Decoys can take many forms from simple emitters that broadcast the real ship’s radar frequencies to persistent, floating, radar reflecting, multi-faceted ‘igloos’. 

 

Similar to electronic warfare, the Navy has given relatively little attention to decoy research and development.  Current decoys are very basic and limited.  What is needed is a decoy that simulates radar, infrared, and visible emission characteristics of the host ship and has a useful degree of persistence.

 

We also need suitable doctrine and tactics for the employment of decoys.  For example, the current tiny handful of decoys embarked on ships is woefully insufficient for a high end naval battle.  We need to be capable of dispersing hundreds of decoys, not a handful.  Let an enemy weapon find the literal one-in-a-hundred signal that is the real ship.

 

Multi-faceted radar reflector

Electronic Warfare (EW) – Despite the fact that historical data shows that EW is far and away the most effective defensive technique, the Navy has virtually ignored EW for decades.  Even the SEWIP modernization program barely pays lip service to the role that EW should play.

 

We need powerful emitters for jamming, false signal injection, cyber attacks, etc. and the entire electronic warfare system must be tied into the Aegis combat system so that it acts in a coordinated fashion.

 

Wake – Our enemies have wake homing torpedoes and no truly stealthy ship would be without wake suppression measures.  Unfortunately, wake suppression is technically challenging and I’m not sure if any practical measures have been fielded.  The Navy has a patent on a wake suppression technique using ultrasonics to reduce/remove the microbubbles in the ship’s wake which are what allow a wake to be sensed and tracked.[1]  Another patent describes a means of reducing wake vorticity (turbulence) by siphoning off the boundary layer of water along the hull.[2]

 

 

Design

 

Having come to an understanding of the various factors that impact stealth, we can now conceptualize a maximum stealth ship design.

 

The ship will be as small as possible with only a minimal superstructure – think a slanted, stealth version of a WWII Fletcher class destroyer superstructure, maybe less.  All surfaces, hull and superstructure, will be fairly sharply angled and will be completely smooth with no protruding pieces of equipment.  The ship will, externally, appear to have no equipment or weapons and items that are necessary for ship handling operations will be fully retractable in one way or another. 

 

Sensors will be either embedded flat panels or retractable with an emphasis on passive sensors providing complete and continuous hemispherical coverage with multitudes of redundant and overlapping sensors.  Even navigation radar will be omitted.  Instead, infrared and electro-optical sensors will provide navigational information.  This may force us to become actual sailors again but that’s not a bad thing, is it?  Radar use will be limited to active weapons employment and even that will be minimized.

 

Weapons will be retractable in various ways.  Even the ubiquitous Mk41 VLS will be modified with a completely flat cover instead of a multitude of separate hatches, each with its own several-sided radar reflecting surfaces. 

 

Except for specific ASW vessels, there would be no helo facilities. 

 

UNREP gear will be fully retractable.

 

This ship will require a complete revision in combat operating procedures.  The overwhelming emphasis will be on passive sensors and greatly reduced communications (none, during combat).  Admirals will have to trust the ship captains to understand their mission intent and then leave them free to execute as they deem best.  The constant verbal diarrhea gushing forth from today’s ships will be a thing of the past.  This ship will operate unseen and unheard.

 

Nothing will be allowed on the ship that does not have a verified, shielded, EMCON operating mode.  The ship will not emit a single stray electron.

 

The ship will embrace bad weather, seeking it out and using it tactically for whatever degree of cover it can provide.

 

The ship will be constantly passively ‘sniffing’ the electromagnetic spectrum for its situational awareness instead of depending on the brute force of radar.  The crew and ship’s systems will be constantly a hair’s breadth from active combat.  Combat systems will have a full auto mode which will be the standard mode in a combat zone.  There won’t be time for human reactions.

 

The ship will be built for war, not cruising.  Silent.  Unseen.  Stealthy.

 

 

 

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[1]https://patents.google.com/patent/US5787048A/en

 

[2] https://patents.justia.com/patent/5222455

 

[3]https://gardnerlaboratories.com/2013/11/22/chemistry-corner-more-color-changing-paint-byk/

 

[4]Discharge into the water will increase the backpressure on the exhaust flow thereby reducing propulsion system performance.  This is an example of prioritizing stealth over speed.

Ship Stealth and Visby

Naval warship stealth is one of the most difficult things to find any data on.  The best information in the public domain consists of nothing more than vague statements like, “smaller radar cross section than a fishing boat”.

Ship stealth consists of more than just radar signature.  Stealth encompasses various aspects, including:

• Radar
• Infrared
• Magnetic
• Acoustic
• Wake
• Visible Light
• Electromagnetic

One of the few vessels that claims to be stealthy and has even a bit of descriptive information is the Saab/Kockums Visby class corvette.

The Visby class corvette is claimed to be the first vessel in the world to have fully developed stealth technology.

“The outstanding stealth properties fundamentally change the ship's survivability and improve its mission effectiveness.” (1)

“Flat surfaces and concealed equipment reduce radar signature to a minimum. The hull is designed on stealth principles with large flat angled surfaces. Every feature that need not necessarily be located outside the hull has been built in or concealed under specially designed hatches.” (1)

The concealed nature of much of the ship’s equipment is a noteworthy aspect.  It has been used on other ships but seldom to the degree that the Visby does.

Naval Technology website quantifies the radar detection range of the Visby.

“A stealth corvette of the [Visby] 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.” (2)

Saab suggests that the vessels small radar cross section (RCS) is due, in part, to the material of construction.

“The vessel is built of sandwich-construction carbon fiber reinforced plastic (CFRP). The material provides high strength and rigidity, low weight, good shock resistance, low radar signature and low magnetic signature. The material dramatically reduces the structural weight (typically 50% of a conventional steel hull). This results in a higher payload carrying capability, higher speed or longer range.” (1)

The carbon fiber material has the added benefit that it conducts electricity and functions to shield radio signals from the ship. (3)

It remains to be seen how the material behaves in combat damage situations.  Does it fracture, does it produce toxic fumes when burned, does it propagate fire, can it be repaired at sea, etc.?

Visby Class Corvette

Other, seemingly minor, aspects of the ship’s radar signature have been minimized.

“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.” (3)

“The paint of the ship’s hull has also been specifically developed to reduce the IR signature.” (3)

Radar cross section is not the only stealthy aspect of the ship’s design.  The turbine exhausts have been relocated from the traditional upper superstructure location to the stern and use water injection to lower the exit temperature.

“The gas turbine exhausts have been concealed in hidden outlets close to the water surface at the stern of the vessel.” (1)

“… the exhaust is water injected which brings down the temperature to just above room temperature before the exhaust exits the hull.” (3)

One can’t help but wonder if the location of the exhausts to the stern is a wise idea.  If a missile does manage to home in on the exhaust, it will hit the stern and cause almost certain loss of propulsion and probably fatal flooding.  On the other hand, if the location combined with the water injection are sufficiently effective then a major heat source has been nearly eliminated.  Unfortunately, I have been unable to find any actual data regarding the thermal reduction effectiveness.

Magnetic signature has also been carefully addressed via an active, dynamically adjusted degaussing system.

“…  the ship has been fitted with an extensive degaussing equipment which renders it without a magnetic signature detectable by a mine. This is achieved by fitting degaussing coils throughout the ship which compensates for the magnetic signature of the on-board equipment. These are laid out in an X, Y and Z grid – the equipment also measures the earth’s magnetic field and compensates for this by adjusting the power to the degaussing system. The larger coils can however only manage the ship as a whole. There are specific steel objects that needs separate degaussing setups fitted. Engines, generators and gearboxes among other things.” (3)

The salient point to all of this discussion is the attention paid to every aspect of the ship’s stealth and the degree to which stealth was pursued.  The American Burke or LCS classes, by comparison, have only rudimentary stealth measures applied, mainly in the form of structural shaping (sloped sides).

Saab presents a fascinating series of photos related to warship stealth which illustrate their claims about ship stealth.

Here is a photo of a U.S. F-117 stealth fighter.  Note the flat, angular panels and lack of protuberances.

Now, here's a photo of the Visby.  Again, note the flat, angular panels and lack of protuberances.  The similarity to the F-117 is striking.

Finally, here is a photo of a U.S. LCS (Freedom class).  The Navy claims that the ship is stealthy but note the many protuberances, round domes, bits of deck equipment, exposed electrical junction boxes, antennae, etc.

Compare the number of projecting bits of equipment in the bow-on photo of the LCS versus the bow shot of the Visby.  It’s clear which one was serious about signature reduction!

Now, the key question is whether the extreme stealth measures of the Visby are worth it.  For example, if the Burke and LCS can’t be detected until the searching platform is within visual range then any further signature reduction – ala the Visby – serves no practical purpose.  Common sense would suggest that the Visby’s extra stealth measures are worthwhile but without data there is just no way to know.

The related question is what impact the Visby’s stealth measures have on the various ship’s system performances.  If the price of some extra stealth is poorer sensor performance, reduced weapon effectiveness, greater difficulty shiphandling, more mechanical problems associated with hidden doors and such, less efficient propulsion performance, etc. then these negative impacts would have to be weighed against the benefits of some incremental improvement in stealth.  Again, without data we just can’t make any judgments.

Regardless, it’s fascinating to see what a maximum, operational, stealth ship looks like and how it’s designed.

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(1)Saab website,

https://saab.com/naval/submarines-and-warships/naval-surface-ships/visby-class-corvette/

(2)Naval Technology website,

https://www.naval-technology.com/projects/visby/

(3)Task Force 72 website, “The Swedish Visby Class Corvette”, Craig Taylor, 18-Nov-2017,

https://taskforce72.org/2017/11/18/the-swedish-visby-class-corvette/