Sunday, April 28, 2013

Stealth for Dummies

Continuing the highly acclaimed (according to ComNavOps' brother-in-law) “Dummies” series, we turn our attention to stealth in warship design.  Just as there was (there isn’t now since they’ve all read the Armor for Dummies post and have been educated !) a group of people who, misguidedly, believed that armor was pointless because it couldn’t totally stop every weapon in existence, so too, there is a group of people (probably the same group) who believes that stealth is pointless since it can’t make a warship completely invisible.  Such a belief could not be more wrong and we’ll now see why.

Most people believe that the purpose of stealth is to conceal the location of a ship – if you can’t find it you can’t attack it.  That’s great except that the naysayers will point out, correctly, that it’s not possible to completely hide a ship with stealth measures.  You can reduce the radar (or visible, or infrared, or electromagnetic) signature to some degree but any ship can be detected.  Let’s face it, we can’t completely mask aircraft and ships are many times larger.  Further, some aspects of ship design just don’t lend themselves to enhanced stealth.  The hull just plain has to be a big vertical chunk of metal.  We can slope the sides somewhat but the hull is still a big radar return.  The same goes for the superstructure.  The various sensors and weapons offer large radar returns and their signatures can’t really be reduced all that much without adversely impacting their function.  Ships need cranes, boats, and deck gear all of which increases the ship’s signature.  So, there’s no getting around the fact that a ship can’t be made invisible.

So, why do we even bother with stealth?  Well, we can reduce the ship’s signature and every bit of reduction makes the ship just that much harder to find.  For a ship attempting to penetrate an enemy A2/AD zone, every hour it can avoid detection is an hour less time the enemy has to attack it or reposition assets to deal with it.  Every hour undetected is an hour of safety making it more likely that the ship will be able to carry out its mission. 

Further, in order to overcome stealth, the enemy will be forced to employ more subs, patrol boats, AEW, and search assets in attempt to increase the density of their search coverage.  This soaks up assets that might otherwise be employed offensively.  So, stealth requires the enemy to assume a larger, more defensive posture than they would prefer.


Enough of a Good Thing or Too Much?

Sooner or later, though, the ship will be found.  What then?  Well, this is where stealth serves its second purpose - a purpose most people overlook.  When a ship is found, what is required to attack it?  The location is, by definition, now known but modern weapons require more than that.  They require a target lock for terminal guidance of the weapon.  That lock may take the form of radar returns, infrared, or whatever.  If the weapon can’t achieve a lock, it won’t strike its target.  It’s that simple.  We could park a ship ten miles off an enemy’s coast, broadcast its location, and, if the stealth measures were good enough, the ship would be invulnerable because the enemy weapons couldn’t lock on.

Is warship stealth that good?  Not hardly! 

So, again, what’s the point of stealth if we can’t totally prevent target lock?  Consider a group of missiles launched towards our ship whose location is reasonably accurately known.  The missiles will be spread out and some will approach the ship on the fringe of the missile’s detection radius.  Stealth reduces that detection radius so that some of the missiles that might otherwise have locked on will miss, never having seen a target.  Of course, some of the missiles will approach dead on and will achieve target lock.  Bad day to be on our ship, huh?  Not necessarily.  Even those missiles that achieve a target lock will have the strength of that lock reduced due to the ship’s stealth.  That allows the ship’s passive defenses such as chaff, flares, and ECM to be more effective.  In other words, a missile with a weak lock is more susceptible to being decoyed than one with a strong lock.  Of course, some missiles will still maintain a sufficient lock for a terminal attack and that’s why ships carry point defense weapons.  Nothing, including stealth, is perfect!

We see, then, that stealth serves not one, but two purposes:  making detection more difficult and degrading weapon locks.  It’s the second purpose, degrading weapon locks, that strikes me as the more important.  In combat, ships will be found.  It’s what happens after that that really matters.  Will the ship survive the inevitable combat to carry out its mission and, hopefully, return home?  Stealth increases the chances of survival.  The notion that stealth must completely hide a ship in order to be worthwhile is just as silly as the idea that armor must completely stop all weapons. 

Like armor, which carries a weight penalty, stealth carries a cost penalty.  Stealth designs are more complex, a bit harder to build, require some additional equipment, and, most significantly, reduce available deck space (look at any stealth warship and compare it to a WWII conventional ship and you’ll see what I mean – the LCS is an extreme example of a stealthy ship that has very little horizontal deck space for mounting weapons, sensors, and gear).  Still, the penalties are well worth it and can be compensated for.  Of course, there’s a balance point in the stealth cost-benefit relationship.  Where that point is, I don’t know.  Has the Zumwalt gone too far?  Only time will tell.

Clearly, stealth enhances the survivability of warships and does so at relatively little cost.  Hey, throw in some armor and you’re on your way to a good ship design!

13 comments:

  1. Since submarines are the stealthiest naval vessels out there, along with the incredible range and lethal effects of modern weapons, why are there no pure sub navies? Cost?

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    1. That's a good question. Indeed, there are those who believe that we (or any Navy, for that matter) should invest far more heavily in submarines.

      To answer your question, though, consider all the tasks, both peacetime and war, that a Navy is called upon to perform. Many of those can't be performed by a sub, or at least not very well. Tasks such as amphibious invasions, show-the-flag diplomacy (a sub, by definition, is hidden - not really suitable for SHOW-the-flag!), anti-piracy, close air support for troops ashore, humanitarian assistance, interdiction and boarding of cargo ships, and so on. Also, remember that a sub is an all-or-nothing proposition when it comes to weapons. Subs can fire Tomahawks or torpedos. There is no option for incremental force. There is no ability to fire a warning shot. A $1+M Tomahawk is not a very cost effective way to take out a sniper, for example.

      I think you get the idea. Navies are called on to perform a whole range of missions, many of which are not well suited to a submarine. Did that help?

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    2. Subs cannot provide:
      Long range/aircraft support
      Long range detection
      Long range interception
      Wide area/theater missile protection/anti-air
      General support/humanitarian services
      etc

      Subs are good for only two things: attack and hunting other subs.

      If all you want to do is blow stuff up, subs are excellent. They can generally get in range undetected, launch, and get away. But they cannot do anything else. They cannot tell you that their is a fleet of aircraft inbound. They cannot put any armor or boots on the ground. They cannot get supplies ashore.

      Now, if we wanted a binary force, where we have two options: do nothing or blow everything up, then subs would be a viable navy. Everything else the navy does however would have to be sacrificed. And that included a lot more than just humanitarian missions.

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  2. Great post CNO. I've argued this same point about ship-based stealth on a number of forums. I'm just going to link back here in the future.

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    1. Thanks, B.Smitty. Happy to help. Feel free to casually drop my name in your daily conversations. Your friends will think more of you for knowing me.

      ...

      OK, that's just ComNavOps having a bit of fun!

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  3. Here is my problem. Many of the ways stealth techniques have problems.

    One of the bad parts is the fault lies in the environment itself.
    The ocean is the world greatest solvent. Everything is mixed in it. (Including uranium but don't tell the environmental crazies that) Including Salt. That Salt coats the special stealth coatings and materials making them just suck at doing their job.
    Add to that the way ships need to be shaped to survive and operate well at sea. The problems with wakes being seen by radar and the naked eye.......

    Then if you have a ship operating in the littorals say the strait of hormuz or other area's you end up with a situation where you are most likely going to be seen constantly.

    Another problem lies in the weapons. AGS (Which i think is not worth the weight and cost penalties associated with it but that is another post) can fire 10 rpm. OK...considering these rounds will then travel high up into a arc and considering on the time to target-9 min for its farthest range...not exactly speedy is it-this means those rounds can be traced back to their starting point. Same for missiles.
    Kinda like the problems with subs. They are found when they launch weapons.

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    1. James, you're kiind of repeating what was stated in the post, that every ship can be found. That doesn't negate the value of stealth as I pointed out. Are you just amplifying on what I said or do you have an additional point? If so, I apologize for missing it. Try again?

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    2. Kind of the problem is that if the ships are covered in radar absorbent material that material is still going to get covered in brine and other wonderful things meaning the ships stealth is then rather terrible.

      So its more its no longer stealthy. Meaning the who idea of counting on that stealth and all of the money invested is...wasted.

      More adding to what your saying. If you can reduce radar signature fine. But don't do it at the expensive of performance, strength or numbers.

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    3. James
      Stealth is more than radar absorbant coatings.
      http://en.wikipedia.org/wiki/File:HMS_Daring-1.jpg
      No special paint, just no clutter.

      For reasons that completely elude me, Radar doesnt see the "Ship", so much as it see the handrails, and so on.
      Any vertical surfaces are far more visible than slightly angled ones

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    4. James & TrT, relatively few ships have radar absorbent coatings. That seems to be more of an aircraft thing. Most stealth on a ship is achieved by use of shape, specifically angled surfaces. Grossly simplifying, stealth is achieved by reflecting the radar waves in any direction except back to the sending radar. Since most radar would be coming from another ship, the radar waves would be parallel along the water (neglecting curvature of the earth) so angled ships would reflect the waves up rather than back to the sending ship. That's why vertical hulls and superstructures are not stealthy. That's also why railings and various ship's fittings are so reflective and detectable; there's always vertical surfaces reflecting back to the sender. Even round railings have a vertical component no matter what the incident angle of the radar wave. The US Navy now uses a kind of angled railing with a triangular cross section. On newer ships like the LPD-17 class the Navy has put the radars, domes, sensors, and whatnot inside a radar reflective "mast" covering to reduce the reflectivity of the various pieces that inherently can't be made stealthy. It works both ways, though. They've apparently had some interference difficulties with the radars inside the coverings to the point that they considered eliminating the mast covering, at one point.

      Hope this helps.

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    5. James, I've never heard that salt water hurts the performance of stealth coatings. Do you have a source for that?

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    6. I'll try to find it. Its not so much that it hurts it as it sticks on the hull.

      And I remember when they found out the stealthy LPD-17 had titanium parts in the mast. Which apparently show up rather well.

      And have you seen the Cut down version they are offering of the LPD-17's?

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  4. Possibly of interest to you, ComNavOps.

    http://www.bloomberg.com/news/articles/2016-10-19/the-feds-won-t-buy-this-19-million-stealth-boat-or-let-it-be-sold-abroad

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