Rail Guns In Combat

One of the topic suggestions from the recent open post was for a discussion of the future of rail guns and lasers so, here it is.  As a follow up to the post on lasers, we’ll look at rail guns In this post.

There are many articles and papers about the technology of rail guns and you can read those on your own.  There are also numerous articles about rail gun improvements and the latest thickness of steel that some new rail gun penetrated.  You can also read all the Navy’s glowing, raving PR announcements about rail guns.  What you can’t readily find is any analysis of the real world combat applicability of rail guns and that’s what we’ll focus on. 

Practical rail guns already exist – practical in the sense that the rail gun and its associated power supply can be fitted on a ship and will fire a projectile that can produce a destructive effect.  However, rail guns have considerations and limitations that, at the moment, preclude any real world usefulness.  We’ll take a look at those conditions and limitations and see what they are and how they impact the future of rail guns as shipboard weapons.

Fire Control

Many people have an image of a rail gun as an almost laser-like weapon that instantaneously hits its target with unerring accuracy.  The reality is that a rail gun, like any conventional gun, is only as accurate as its fire control system.  The high velocity of a rail gun projectile imparts no magical accuracy.  What it does is reduce the target’s time to evade but the inherent accuracy is no better or worse than any other gun.  For a kinetic (hit to kill) projectile, accuracy is an all or nothing proposition.  A miss by one millimeter may as well be a miss by a mile.  For the case of a proximity fuzed projectile, close counts and this is where the higher velocity and reduced evasion time may improve the odds of a successful hit but, still, the inherent accuracy is unchanged over conventional guns.

If you haven’t yet, take a look at any of the numerous live fire gunnery exercise videos available on YouTube.  What stands out about all those videos is the extraordinarily high percentage of misses.  A very broad visual estimate ‘average’, based on splashes versus flashes (impacts), suggests an accuracy of 10%.  Note, that these gunnery exercises are, invariably, conducted under ideal conditions where the target is generally stationary or moving fairly slowly in a steady, predictable path and the firing ship is also stationary or moving in a slow, steady line.  Weather conditions are always perfect and seas are almost always calm.  This is about as far away as one can get from real world combat conditions where both the target and firing platform will be twisting, turning, rolling, pitching, disappearing in waves, vibrating due to speed, etc.  Even so, under these near perfect conditions, the accuracy is around 10%.  What does that suggest for real world accuracy?  For example, the Vincennes airliner shootdown incident involved around 100 5” rounds fired at Boghammers with no verified hits.

What does this mean?  Again, for kinetic projectiles, a direct hit is the only beneficial outcome.  A near miss is a miss.  Fire control will be key to the success of a rail gun.  This suggests that proximity fuzed, explosive projectiles may be desirable, however, such projectiles also negate one of the major claimed benefits of rail guns which is the cheapness of inert projectiles.  Once we begin incorporating sensors, circuitry, explosives, fuzing, shrapnel or scoring to produce shrapnel, etc. the costs quickly escalate. 

Explosive projectiles also negate another claimed major benefit which is the inertness of the projectiles and resultant safety of the non-explosive magazine storage.  This suggests that while proximity projectiles might be useful, the advantages of rail guns are maximized only with inert, kinetic projectiles – almost a contradiction in terms.

The solution to rail gun fire control shortcomings is the same as for conventional guns: guided projectiles.  Of course, adding guidance control sensors, circuitry, and mechanical fins negates the major claimed benefit of rail guns which is the cheapness of inert projectiles.

Lethality

Let’s now turn our attention to lethality.  For a conventional explosive shell, lethality is high.  Why?  This isn’t a trick question.  It’s because the shell explodes!  The explosion produces an area of damage many times larger than the shell, itself.

An explosion taking place in or near the target is very likely to damage or destroy something critical to the target and produce the effect of destroying it.  For a rail gun, however, it is quite possible that the projectile may cause little or no damage despite its great kinetic energy. 

For example, a rail gun projectile hitting a thin skinned aircraft would likely pass straight through without converting its kinetic energy (relax – I’m taking liberties with the strict definitions provided by physics) to heat.  This is the bullet through a piece of paper scenario.  If the target has insufficient resistance, the projectile will not ‘shed’ its kinetic energy into the target.  Of course, in the case of the aircraft, the projectile might well hit something critical to the operation of the aircraft during its momentary passage through the aircraft.  On the other hand, there are many non-lethal ‘paths’ through an aircraft.

A rail gun projectile used against a small boat would be mostly useless.  The projectile would pass straight through the boat, causing only a small hole unless it happened to hit the engine or a control cable.  It’s easy to see that a rail gun would be largely ineffective against a small boat swarm.

Another case is a rail gun kinetic projectile used in land attack.  If the projectile hits a target with sufficient resistance it will do significant damage.  A building, bunker, or thick skinned, heavily armored vehicle like a tank would likely suffer great damage.  However, if the projectile hits the ground just inches away from the target, the projectile will penetrate deeply and continue moving until it runs out of kinetic energy.  The result will be a puff of dirt and … nothing else.  Thus, a kinetic energy projectile is useless for area bombardment unless it just happens to hit something substantial.  Unlike an explosive projectile which can do damage with a near miss, a kinetic projectile has zero near miss damage potential.

The case of a kinetic projectile used against a ship is another case of a thin skinned target.  The projectile would likely pass straight through without ‘shedding’ much energy.  The ship would be left with a few inch diameter hole clean through and not much damage.  There is relatively little in a ship that would result in significant damage from a narrow hole being drilled through it.  Of course, one could always get lucky.

It’s obvious that a kinetic projectile has the potential to inflict great damage but only against targets with sufficient resistance.  Have you ever wondered why every rail gun test video used giant plates or blocks of thick steel as the target?  It’s because if they used, say, 3/8” sheet metal that is typical of a ship’s hull, the projectile would likely pass straight through with no visible effect – it wouldn’t make for a very impressive video!  This observation also makes it obvious that an explosive rail gun projectile (again, negating the benefit of an inert magazine!) is needed if we wish to effectively cover the full range of targets. 

Size, Rate of Fire, and AAW

Rail guns are fairly large machines – on the order of a 5”-8” naval gun.  This is not a major problem, merely a characteristic as ships are sized to be able to accommodate weapons of that size.  However, hand in hand with size goes rate of fire.  The larger the projectiles, the more energy that is needed to fire them.  The energy causes heat buildup on the ‘barrel’ of a rail gun and limits the rate of fire (along with cyclic power requirements and limitations). 

One future developmental avenue for rail guns is to significantly decrease the size and increase the rate of fire.  One can imagine this being used to create smaller anti-aircraft rail guns with very long ranges and very high rates of fire – think CIWS on steroids.  The high velocities would minimize the target’s time of evasion and enhance the chances for a hit although, like conventional guns, explosive shells with proximity fuzing would be required to be effective.

Range

While rail gun proponents make enthusiastic claims about the range of rail guns, the range must be recognized to be relative.  Yes, the range is significant compared to conventional guns but it is insignificant compared to the other readily available methods of delivering ordnance against typical inland strike targets.  Aircraft and missiles, for example, are numerous, readily available, and far outrange rail guns.

Applicability Summary

So, where does this analysis leave us?  It appears that, in order to produce destructive effects, rail guns will require targets with sufficient resistance to cause the projectile to ‘dump’ its energy into the target.  This suggests that the applicable target set will be thick concrete structures like buildings and bunkers, heavy vehicles like tanks, fortifications, and very large ships like carriers or large cargo vessels.  The challenge, even for this target set, is fire control.  A near miss with a kinetic projectile produces zero effect.  The obvious solution, a combination of guidance and proximity fuzing, would completely negate the major claimed benefit of rail guns which is the cheapness of the projectiles and would totally negate the claimed safety benefit of non-explosive magazines.  The overall conclusion seems obvious – rail guns have a very limited and specific target set.  They cannot be a general purpose weapon.

Naval Rail Gun Concept Image

Historically, the main target set for a naval gun is land area bombardment.  Even in WWII, ship against ship engagements were the rare exception, not the rule.  Shore bombardment was far more common.  Kinetic rail guns are next to useless for this application.  This, alone, has to lead one to wonder why we would install rail guns on ships.

The anticipated target set suggests that the most useful application for rail guns will be as land attack weapons against known, fixed targets.  Unfortunately, this is a fairly limited target set.  In a peer war, most battlefield targets will be hidden, think skinned, or mobile.  To mount a sizable weapon, like a rail gun, on a ship means using valuable hull and deck space for a weapon with limited usefulness.  That’s going to be a tough sell to naval ship designers.  I can see two likely ship mounting scenarios for rail guns:  very large ships (cruiser size and larger) that can afford the space for a limited use weapon and/or a much smaller, dedicated rail gun vessel akin to the old monitors.

We could build a rail gun armed ship that could deliver shells, whether kinetic or explosive, some 50, 100, or 200 miles (depending on what claim you want to believe about rail guns) inland from the sea – actually, given some reasonable stand off distance from shore, you’d have to subtract 5-50 miles from those range numbers – but we already have artillery of various sorts that can achieve those ranges and reach out to 300 miles (ATACMS, for example).  A rail gun, then, would be a duplication and an expensive one at that if we have to build an entire ship to mount it!

In short, rail guns are a technically viable weapon, albeit one with a very limited target set and, in its most useful configuration (explosive carrying and proximity fuzed), negates the major claimed benefits of cheapness of projectiles and inertness of storage.

Disclaimer:  This is, by its nature, a highly technical topic in its underlying foundation and I am not a rail gun expert, by any means.  Some of my assumptions about the technology may not be completely correct and I welcome any discussion that can correct and enhance our grasp of the topic.  What I will not welcome is ‘gotcha’ type comments, even if correct.  This is an attempt at a discussion, not a contest to see who can score the most points.

... And What's Behind It

One of the four major rules of gun safety is to be sure of your target and what’s behind it.

In WWII, we frequently caused friendly fire damage and casualties by firing at attacking aircraft within the task force and hitting friendly ships behind and beyond the target aircraft.  It was almost unavoidable and considered an acceptable and necessary unfortunate consequence of trying to prevent a ship from being hit and sunk.

The same problems and concerns occur during infantry firefights and urban streetfights as well as during tank battles.

The same problem has occurred with Phalanx CIWS.  Here’s an example from Wiki,

“On 11 October 1989, USS El Paso was conducting a live-fire exercise off the East Coast of the United States using the Phalanx against a target drone. The drone was successfully engaged, but as the drone fell to the sea, the CIWS re-engaged it as a continued threat to El Paso. Rounds from the Phalanx struck the bridge of USS Iwo Jima, killing one officer and injuring a petty officer.”

And another from Wiki,

“On 25 February 1991, during the first Gulf War, the Phalanx equipped frigate USS Jarrett was a few miles from the US battleship USS Missouri and the British destroyer HMS Exeter. The ships were thought to be under attack by an IraqiSilkworm missile (often referred to as the Seersucker), at which time Missouri fired its SRBOC chaff. The Phalanx system onJarrett, operating in the automatic target-acquisition mode, fixed on Missouri's chaff, releasing a burst of rounds. From this burst, four rounds hit Missouri which was 2–3 miles (3.2–4.8 km) from Jarrett at the time. There were no injuries.”

Note that we’re not discussing the closely related issue of identification/misidentification.  This post is concerned with the issue of stray rounds impacting friendly forces behind and beyond the target.  The distinction is critical for the discussion.  With this issue, identification is not a problem.  The friendly forces are well known and their location is clearly observed.  The problem is rounds that don’t hit the target and continue on to strike a friendly unit. 

Okay, this is a tragic but almost unavoidable consequence of close combat, especially in naval scenarios where friendly ships may be spread out over many miles and enemy aircraft, ships, and missiles can penetrate the force and intermingle with friendly forces but what’s the point?  The point is that with the advent of rail guns, lasers, and hyper velocity projectiles (HVP) that we’re all so excited about, the behind and beyond issue becomes immensely larger and more deadly.  For example, CIWS rounds have a range of couple miles.  A friendly ship that is in the line of fire but five or 10 miles beyond is perfectly safe.  However, with rail guns, lasers, and HVP’s, the behind and beyond range borders on unlimited.  We could miss a target that’s one mile away and inadvertently hit a friendly task force 50 miles beyond!

Consider the case of an enemy missile that has penetrated the perimeter of a naval task force spread out over many miles.  What might have been an adequate safety margin in WWII is now non-existent with lasers, rail guns, and HVPs.  Potentially, this means that far fewer, possible no, ships can fire on the incoming missile out of fear of hitting a friendly unit many miles beyond and behind the target.

Consider the case of a naval task force 50-100 miles from land and trying to defend itself using lasers, rail guns, and HVPs.  Misses in the direction of the land may see the land showered with projectiles and lasers.

Could we be hobbling our defensive fires by moving to lasers, rail guns, and HVPs?  At the very least, our zone of awareness will have to increase from a couple of miles to dozens or hundreds of miles.  In a situation like the Middle East or the first island chain, there may not be a safe direction in which we can fire!

Basic Gun Safety On A Grand Scale

I’m not suggesting that we don’t adopt lasers, rail guns, and HVPs but I do hope that someone is looking very carefully at the implications and impact on our defensive doctrine and tactics rather than just blindly pursuing the technology “just because we can”.  Sadly, like the Navy that forgot to check whether the LCS helo could safely tow the mine countermeasures equipment and then found out the hard way that it couldn’t, I’m fearful that we aren’t looking at the “behind and beyond” issue and won’t recognize it until it’s too late.  I just see a bunch of future laser and rail gun armed escorts paralyzed and unable to fire defensively because of friendly units and land dozens or hundreds of miles away.

Rail Gun Projectile Cost

Wait, what now?  I thought the rail gun was supposed to be able to fire rocks that cost pennies apiece?  Now we’re being told that the rail gun projectiles, filled with tungsten pellets, will cost $25,000 - $50,000 each (1).

One of the selling points of the rail gun was that the projectiles would be much cheaper than any existing munition because the projectile would be an inert lump.  Now, it seems that’s not the case

We’ve already talked about the limitations of a rail gun, chief of which is that it doesn’t explode which makes it useless as an area bombardment weapon.  It’s limited to pinpoint impact on fixed targets.

A second limitation is that the projectiles are unguided although a guidance package is being studied.  Thus, the projectile can’t track moving targets and can’t accept laser guidance.  The targets must be fixed and the co-ordinates known.

Now, we have another limitation and that is munition cost.  At $50,000 per projectile (it’s always the higher cost and you can safely assume that cost will go even higher) we can’t just go flinging these things around.

Could it be that rail guns not quite the miracle we were led to believe?

___________________________

(1)Wall Street Journal website, “Faster Than a Speeding Bullet - A First Look At America’s Supergun”, Julian Barnes, 30-May-2016,

http://www.wsj.com/articles/a-first-look-at-americas-supergun-1464359194

Railguns

As reported by Navy Times website, Adm. Jonathan Greenert, Chief of Naval Operations, listed his technology and developmental priorities while speaking at the Naval Future Force Science and Technology Expo (1).  Prominent among those priorities was,

“Getting off gun powder. Lasers and railguns will provide an incredibly deep magazine at remarkably low cost, he said.”

ComNavOps fully supports laser and railgun development efforts while, at the same time, recognizing the many technological challenges still to be overcome before those technologies can be applied on a practical basis.  Let’s set the technological challenges aside and look at some of the tactical and application issues that may not have been fully explored, yet.

Consider an arrow shot at a piece of paper.  The arrow will pass through the paper and leave a fairly large hole in the paper although the rest of the paper will be unaffected.  Fast forward on the technology scale and consider a bullet fired from a handgun at a piece of paper.  The bullet is much more advanced technology and much more powerful than an arrow so it should do much more damage, right?  Well, the bullet will pass through the paper and leave an even smaller hole than the arrow.  How can that be?!  The bullet is faster, more advanced, and more powerful.  The problem is that a bullet is an inappropriate weapon choice for a paper target. 

With that example in mind, let’s consider a railgun firing at a modern, small naval vessel.  You’ve probably seen the videos of test firings of railguns penetrating a foot of steel and the resulting destruction due to the kinetic effects.  However, as you know, modern small vessels such as corvettes and frigates are lightly built and thin skinned.  What will happen when a railgun projectile traveling at several times the speed of sound hits a modern vessel?  Well, the projectile is inert so there won’t be any fused explosion.  It has no unexpended fuel to disperse and ignite.  That leaves only kinetic effects but will the projectile encounter enough resistance to transfer its kinetic energy to the target, thereby causing damage or will the projectile pass through the thin skinned vessel without doing significant damage much like the bullet passing through the paper?  One could imagine a targeted vessel with a bunch of small, clean holes but otherwise largely undamaged after being engaged by a railgun.  I can’t answer this question and I may be completely off base but it’s at least a plausible scenario to ask about.

Now, let’s look at area effects.  One of the main uses for a naval gun has, historically, been to produce area explosive effects during land bombardment for area damage, suppressive fire, and similar uses.  Once again, consider how a railgun works.  The projectile is non-explosive and depends on the transfer of kinetic energy for its effect.  In short, it does not produce an area effect.  It is not really possible to provide area bombardment or suppressive fire from a railgun.  A railgun projectile hitting ground will kick up little dirt and bury itself. 

What about guidance?  Railguns are touted as shooting projectiles at such great speeds that they will strike before the target can move.  At close range, that may be true but railguns are being looked at as deep strike weapons hitting targets hundreds of miles away.  Do the math.  It still takes significant time to cover that distance.  Mobile targets, such as vehicles, will be well out of the path of a railgun projectile by the time it arrives.  Remember, with no explosive effect, a projectile must have a direct hit to be effective.  A miss of one foot is a total miss.  There is no area explosive effect to compensate for small misses.  Well, why don’t we add a guidance package to the railgun projectile?  Wouldn’t that solve the problem?  The answer is no, for two reasons.  First, we don’t have the technology to fit a guidance package into a projectile and have it survive the firing.  The stresses on the projectile are immense.  Second, if we start adding guidance packages (or ECM, or active radar, or whatever) we negate the main advantage of the railgun which is its cheap projectile cost.  Instead of shooting free rocks as projectiles, we’ll be right back to $50K+ projectiles like we have now.

Now let’s consider a railgun in an AAW/CIWS role.  Similar to a Phalanx CIWS, a railgun could be an effective AAW weapon especially given its very high speed and, thus, short travel time to the target.  Further, the low cost of projectiles makes it an economically viable counter to modern missiles.  The downside is that the great speed of the projectiles ensures a very long range which, if the projectile misses, makes it a potential friendly fire hazard for ships and aircraft much further downrange as opposed to the relatively very limited range of a Phalanx CIWS, for instance.

We see, then, that a railgun is akin to a sniper weapon.  It’s great for specific, fixed targets but suffers from significant limitations due to its non-explosive characteristic and inability to be guided.  A railgun could supplement and complement a conventional gun but it can’t totally replace it.

(1) Navy Times, "CNO wants more high-tech assets, delivered quickly", Lance M. Bacon, 4-Feb-2015,

http://www.navytimes.com/story/military/2015/02/04/greenert-future-force-expo-technology-priorities/22856343/