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.