2009/02/12

Warship stealth

.
Galrahn at the USNI blog and Burleson at the New Wars blog have questioned the 'stealth' approach to naval surface combatants that has shaped the look of new warships since the early 90's. The polygonal look with much less railings and antennas as well as weapons mostly hidden is a very different look in comparison to 60's, 70's and most 80's designs.

Stealth for naval surface combatants is mostly an affair in the realms of electromagnetic waves (radar), acoustics (against passive sonar) and as I understand it usually also magnetism (to counter magnetic mine and possibly even torpedo fuzes).

Infrared camouflage efforts are almost pointless - published thermal photos of warships at sea show such a stark contrast between the ship and the surroundings that only the use of the (decontamination) shower system seems to be promising (afaik). Such a water spray system has even been used on a CV90-based demonstrator tank as active infra-red camouflage system for a tank, but it's certainly only a temporary camouflage (requiring a timely alert, something that was often missing in past missile vs. ship actions).

The East African pirates are more 'stealthy' than all those easily identified 'stealth' warships which are low-observable at best. They use disguise for stealth instead of low reflexivity. You see them, but you cannot identify them as what they are unless you search their ship. The same principle as used by intelligence services, ninjas, criminals, and most insurgents.

Stealth warships aren't invisible to radar, and could never be invisible to good airborne radars if the latter were looking down at a good angle.
Let's assume that the ship reflects no more electromagnetic energy than the water surface (and even so to all directions), a generous assumption in my opinion.
The ship couldn't move much faster than 5 knots unless it's one of the prototypes for minimum wave effects. Radars can 'see' bow waves easily at long distances - and a bow wave without a ship would be a dead give-away even if the warship is trying to hide among hundreds of civilian ships. 5 knots is often unacceptable (but at least usually very silent).
The next problem is the ability of radars (with high frequencies) to create 3D images of objects. An uninteresting ship like a freighter could easily be pictured like that, but a stealth warship would either prevent it (very suspicious) or be easily recognized as warship on the screen.

I am convinced (for the time being ) that stealth is impossible for naval surface combatants against good aerial radars at good angles. Low observable characteristics are credible, though. A mix of reduced signature, decoys and jamming is useful against the tiny radars in anti-ship missiles, and low observable characteristics make the initial detection tougher at long ranges. LO adds to the challenges for the opposing force, but it's farther away from an invisibility cloak than an infantryman's camouflage clothing.

By the way; 'radar stealth' isn't really that new for navies. Radar absorbing materials (RAM) have been used since the 70's or maybe 60's on masts to reduce problems with the radars mounted on the masts.
Some German submarine snorkels of WW2 were already fitted with radar-absorbing mats and experiments for RAM date back to 1942 at least.


Galrahn pointed out that the shape is too distinctive, supposedly 'stealthy' (surface) warships cannot really avoid identification once they've been detected.
He sees a significant difference between blue water (high seas) and brown water (coastal waters) requirements for stealth. In the littorals you need to look like other ships, the supposed ability to fool radars is only useful against enemy munitions, not so against enemy reconnaissance.


Let's look at modern naval military history for inspiration:

We had stealth warships before.

Pirates, Q ships (anti-submarine traps) and merchant raiders (Germans both WW) disguised themselves as unarmed or marginally armed civilian ships just to drop the disguise when they demanded immediate surrender of their victim or began to sink it right away (if the victim is a capable opponent, as in the case of Q ships and Kormoran vs. HMAS Sydney).

The merchant raiders (Hilfskreuzer, auxiliary cruisers) offered huge internal volume and the ability to morph their outer appearance to many different ships. Some changes to the superstructure, hidden weapons, new paint job and changed name were enough to confuse and make identification very difficult.
The German merchant raider Kormoran was able to fool the Australian light cruiser HMAS Sydney by pretending it's the Dutch merchantman Straat Malakka till a distance of 1500 m - close enough to make the firefight deadly for both.
A stealth warship would have been identified at 10,000+ m without binoculars.

The shapes of merchantmen could easily be copied by modern warships - it's just a matter of intent or not.
Another possibility would be to have a close look at the container and MEKO technology - and possibly turn merchantmen into warships. Such ships wouldn't be milspec and would fare poorly once hit. Nevertheless, such auxiliary cruisers might still have their niches.

Sven Ortmann

edit :
I'd like to add that we could also take 19th century monitor designs and WW2 German submarine attacks for inspiration and delete most of the freeboard. Such a semi-submersible ship could disguise its turret/superstructure as a very small ship and keep its real size invisible.

1 comment:

  1. A new monitor like the Zumwalt-class?
    You have a point so stealth serves two purposes, makle finding a warship harder and make targeting the located ship harder. What do you think about USV that can switch to low stealth and imitate surface combat ships for enemy radar? Wouldn't the use of active emission searching be a giveaway of own installations for a dubious result? However, I agree that there's no cloak to make yourself unidentifiable.

    ReplyDelete

Use a nickname and stick to it! I may block anonymous comments. Offensive comments may also be blocked, in part due to the duties of a blogger in Germany.