The Swedish Navy is testing out a new ship which is believed to be the most "invisible" yet. The Royal Navy and the US Navy both have plans of their own for similarly futuristic "stealth" ships. BBC News Online investigates the shape of the future of naval warfare.
By Chris Summers
BBC News Online
Ever since radar was first used by the British shortly before World War II, military boffins have been trying to think of ways to beat it.
The Visby is designed to have a low key radar signature
The US Air Force invented the first "stealth" aircraft, the F117, and the B-2 bomber, in the 1980s.
Both planes were designed in such a way as to keep their radar "signatures" to an absolute minimum.
Now naval architects have come up with a similar way of beating the radar.
The first Visby corvette, designed by the Swedish shipbuilders Kockums and built at their Karlskrona yard, has just completed sea trials with the Royal Swedish Navy. It will come into service in January and will be followed by four more.
WAYS OF SPOTTING SHIPS
Visually - either with the naked eye or by satellite (can depend on cloud cover and darkness)
Radar - invented in 1940s (new ships aim to reduce radar "signature")
Sonar - primarily used by submarines (new ships have quieter engines and special paint which can deflect sonar)
Infra-red - Many missiles use heat-seeking systems to track enemy vessels (new ships are specially designed to mask heat sources such as engines)
American designers are working on the US Navy's own fleet of stealth ships, the DD(X) destroyer, which is due to enter service in 2011.
Northrop Grumman Ship Systems is leading a consortium which has been given the $2.8bn contract to build the futuristic ships.
Northrop Grumman spokesman Brian Cullin told BBC News Online: "The DD(X) will be as revolutionary as the Dreadnought was when the British introduced it at the turn of the last century."
He said the DD(X) would save the US Navy a fortune in running costs because it would have 200 fewer sailors to operate it than the existing Arleigh Burke class.
Mr Cullin said it would also be more efficient for the US Treasury.
"In the Iraq war last year the Navy was firing Tomahawks at $1m a piece. Projectiles for the DD(X) will cost significantly less and it will be able to fire large volumes of surface fire at close range, which will bring huge economies."
Displacement: 14,000 tonnes
Speed: 30 knots
Cost: $2.8bn (£1.5bn)
Replaces: Arleigh Burke destroyers
As for the Royal Navy, it too will have a new breed of stealth ships in action soon. HMS Daring, the first of the Type 45 destroyers, is being constructed at BAE Systems' Govan and Scotstoun yards in Glasgow. It is to due to enter service in 2007.
But the Swedes are in the lead, with the Visby.
It is constructed almost entirely of carbon fibre, the same material used to make the chassis of Formula One cars and the hulls of racing yachts.
Its angular design gives it a minimal radar signature, known as a cross-section, and its 57mm cannon can also be retracted to reduce it still further.
John Nilsson, one of the designers, told BBC News Online: "We are able to reduce the radar cross section by 99%. That doesn't mean it's 99% invisible, it means that we have reduced its detection range."
Displacement: 600 tonnes
Speed: 35 knots
Hull: Carbon fibre reinforced plastic
Cost: £100m ($184m)
In a nutshell, if the Visby was 100km from an enemy vessel it could see the enemy on its radar but not vice versa. It could get within 30km of the enemy before being spotted.
Carbon fibre is also a lot lighter than steel and the Visby, at 600 tonnes, is half the weight of a conventional corvette.
Mr Nilsson said: "Naval officers fall in love with [this] ship. It's not classically beautiful. In fact it looks like a lunchbox. But it has better manoeuvrability and can achieve that level of stealth."
A Ministry of Defence spokesman said naval designers have known for a long time that radar signatures depend on the angles involved.
He said: "The trick is to avoid right angles, which reflect radar right back.
"We use a secret angle on our Type 23 frigates which enables our ships to reduce their radar signature to an absolute minimum."
TYPE 45 DESTROYER
Displacement: 7,350 tonnes
Speed: 27 knots
Cost: £286m ($500m)
Replaces: Type 42 destroyers
John Fyall, of the Defence Procurement Agency, said: "Our new Type 45 destroyers will use much of this technology to reduce their radar signatures.
"The whole idea is to make it look like it's not a big ship."
A BAE Systems spokesman said the design of the Type 45 and the materials used would reduce its radar visibility but he said the hull would be steel, not carbon fibre.
He said: "It will provide the future backbone of the Royal Navy as it faces multiple threats."
State of the art
The MoD spokesman questioned the "survivability" of ships made of carbon fibre, and also doubted whether they could be able cope with ocean conditions.
Mr Nilsson said the Visby - which is 73m long - was only designed for littoral, or coastal warfare, but he said they had designed a 120m ship which had worked well technically.
As for the question of survivability, he said: "It is not so much a question of material but physical size. Any ship below 100 metres, regardless of material, will be gone if it's hit with a modern surface-to-surface missile."
The new ship is also controlled by state-of-the-art computers using a Windows NT operating system.
But Kockums and the Swedish Navy deny it could be sabotaged by hackers and say that even if it did they could fall back to traditional steering and navigation.
Mr Nilsson said: "I am not an expert in computer security but we have focused a lot on that and this ship has a lot of firewalls and clever ways of avoiding it (being hacked)."
Commodore Stephen Saunders, editor of Jane's Fighting Ships, said: "Stealth is not an end in itself. The value of a ship is in what it can deliver.
"Undeniably having a stealth ship allows you to operate in places where you might not have been able to operate."
He said one potential flashpoint where they may be useful was around Taiwan, in the event of a clash between the US and Chinese navies.
But Commodore Saunders said: "Ships will never be completely invisible.
"A lot of modern submarines are extremely hard to detect, but that is always going to be difficult for a surface ship to match."