Lasers 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.  We’ll look at lasers in this post and then rail guns in a second post.

There are many articles and papers about the technology of lasers and you can read those on your own.  There are also numerous articles about laser power improvements and the latest thickness of steel that some new laser burned through.  You can also read all the Navy’s glowing, raving PR announcements about lasers.  What you can’t readily find is any analysis of the real world combat applicability of lasers.  It’s pointless to develop a laser with a city block of dedicated power generating equipment that can burn through two feet of steel in only ten minutes because none of that is applicable in a real world combat situation.  We’ll focus on the real world considerations.

Practical lasers already exist – practical in the sense that the laser and its associated power supply can be fitted on a ship and will produce a coherent beam that can, under the right conditions, produce a destructive effect.  However, the ‘right conditions’ generally preclude any real world usefulness.  We’ll take a look at those ‘right conditions’ and see what they are and how they impact the future of lasers as shipboard weapons.

Dwell Time

Barring development of the far, far future (in a galaxy far, far away) Star Wars type lasers that instantaneously disintegrate whatever they touch, lasers in our lifetime will be limited to prolonged contact types.  That means just what it says – that in order to produce a destructive effect the laser will have to maintain contact with the target for an extended period (dwell time) and, what’s more, that contact will have to be on the same pinpoint spot to allow the laser enough time to ‘burn through’.  Even ‘burning through’ the initial material of the target may only be the first step in destruction of the target.  For example, a laser hitting a missile will have to burn through the outer shell of the missile, which will have no effect whatsoever on the missile, to reach the inner works of the missile that can, in turn, be burned to, hopefully, produce the desired destructive effect on the missile.

Of course, for a smaller, more fragile target, like a small quadcopter or UAV, the outer contact may be sufficient on its own to destroy the target by, for example, shearing off a fin/wing or destroying a propeller hub.

The developmental goal in laser development will be to produce effects with less and less contact time (more powerful lasers), ultimately moving towards the Star Wars instantaneous disintegration.

Dwell time is a function of the system’s fire control.  Whatever fire control aiming system we’re using has to be fine enough to maintain laser dwell for the required burn through time.  Consider what that means, today.  A laser fire control would have to be able to maintain contact on the exact same spot of, say, a missile while it moves at Mach speed and jinks in terminal approach while the laser firing platform (our ship, presumably) also moves, maneuvers, rolls, and pitches.  That is some exquisitely fine fire control and nothing like that is even remotely possible today. 

Yes, we have stabilized fire control but that’s exceedingly crude by comparison.  Motors are used to move the firing weapon (guns, currently) in train and elevation to stay on target.  Consider what that means, however.  It means staying close enough on the target to achieve, at best, a 10% hit rate somewhere on or near the target.  Do you grasp how far that is from maintaining a pinpoint lock on a target when both the firing platform and the target are moving fast and maneuvering violently?  You’ve seen videos of Navy tests where a laser slowly destroyed a small boat motor or a UAV but have you seen a video of a speeding, maneuvering shipboard laser destroying a fast, violently maneuvering target?  Of course you haven’t because it can’t be done!

The real world consequence of extended dwell time is extended engagement time.  If we have a battery of shipboard lasers defending against an incoming volley of anti-ship missiles and each individual missile engagement requires a dwell time of, say, 30 seconds, to make up a number, you can readily see that, given the Mach speeds of the incoming missiles and the resulting minute or so engagement window (we’ve run through the arithmetic on this in previous posts or you can run through it yourself), we’ll only be able to engage a few missiles before the remainder reach us.  In comparison, bullets (CIWS) or defensive missiles (SeaRAM or ESSM) can be fired at numerous targets simultaneously (well, nearly so for the purposes of this discussion) and a hit will produce an instantaneous kill.

In order to be effective in real combat in the AAW role, a laser system has to produce a kill in about 10 seconds or less.  Any more than that and you simply can’t engage enough targets to mount an effective defense. 

One way to compensate for longer dwell time is to increase the number of defensive lasers.  We’ve noted that the number of close range SeaRAM and CIWS systems on modern ships is far too few for an effective defense and the same situation would apply to lasers.

Lethality

Let’s now turn our attention to lethality.  We’ve already noted that laser lethality requires dwell time.  Assuming we’ve achieved that, we now need lethality.  For a conventional explosive shell, lethality is high.  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 laser, however, it is quite possible that the focused beam, being relatively quite narrow and having no explosive effect, may damage or destroy something that is not critical to the target or not critical in a relevant time frame.  For example, a laser may burn through the exposed motor shell on a small swarm boat only to hit and damage an exhaust port underneath which is not critical to the engine’s continued performance, at least for the time needed for the boat to complete its attack.  Or, a laser may burn through the shell of a missile only to hit an empty fuel tank or an ECM component, neither of which would stop the missile.  Consider the case of a laser used against a ship and imagine a narrow beam passing through the ship on a straight line.  With no explosive effect, the odds of the beam hitting a component that would destroy or mission kill the ship is near zero.

One conclusion from this analysis is that lasers will work best when the target is most densely packed with critical components.  Thus, quadcopters, UAVs, and missiles would be more susceptible to laser effects while large aircraft and tanks would be less susceptible and ships would be nearly invulnerable.  This suggests the target classes we should be developing lasers for.

Power

Lasers require a great deal of power although I would imagine that the power can, and is, supplied in pulses (a capacitor like function).  Thus, it’s not necessary to provide continuous power but only pulses of power.  I’m way out of my field here so feel free to correct me if I’m wrong.  This is interesting and has implications for power management and power system architecture but is only marginally relevant to this discussion.  What is relevant is the need for power, however it is supplied.  If the power is disrupted the laser is rendered inoperative.  Power represents a single point of failure for a ship’s entire battery of lasers.  Lose power and you lose all the lasers.  Of course, this applies to conventional guns as well.  Ideally, what you’d like to see is a local power system that can continue to operate if the main power is disrupted.  To an extent, conventional gun systems of WWII had this capability with local fire control and, for smaller guns, local manual train and elevation.  For lasers, the analogous local capability would be a battery or capacitor backup that could supply power for at least enough shots to continue the immediate engagement before ultimately failing.

Countermeasures

As with all weapons throughout history, the implementation of laser weapons will be immediately followed by the implementation of countermeasures.  If the countermeasures turn out to be cheaper than the weapon, then the weapon is on the wrong side of the cost curve and will be at least an economic failure, if not a practical failure.  Early anti-ship missiles were expensive and the early countermeasures, such as chaff and flares, were very cheap.  Eventually, the curve flipped and now we see that anti-ship missiles are far cheaper than the defensive Aegis/Standard weapon.  So goes the perpetual back and forth of weapons and countermeasures development.

Lasers of the foreseeable future are susceptible to countermeasures.  Noting the requirement for significant dwell time, simple countermeasures could include ablative coatings, reflective coatings, ‘rolling’ to prevent extended contact (rolling airframe missile?), multi-shelled sacrificial layers, jinking, sea skimming to reduce the engagement window (lasers are, of course, line of sight and the engagement range against a sea skimming target is around 15 miles or so), stealth to deny fire control solutions, and many other possibilities that I’m sure I haven’t thought of.  The takeaway from that list is that most of the possible countermeasures would be very cheap to implement relative to the cost of the laser – in fact, some already exist.

Thus, for the foreseeable future, lasers appear to be on the wrong side of the cost curve.

Applicability Summary

So, where does this analysis leave us?  It appears that, in order to produce destructive effects, lasers will require small, slow targets so as to maximize the chance of achieving sufficient dwell time.  This suggests that the applicable target set will be drones, UAVs, and small boats.  The challenge, even for this target set, is fire control.  Laser development would do well to go on hiatus and instead focus (a laser joke there - sorry) on fire control.  To put it simply, the key to effective lasers is dwell time and the key to dwell time is fire control.  This also suggests that the most effective lasers will be land based which eliminates one half of the movement issue.

With sufficient fire control, there is no reason why lasers can’t be quite effective for the small, slow target set.  Interestingly, the anticipated target set suggests that the most useful application for lasers will be on land as anti-drone weapons.  That being the case, the development trend should be towards smaller lasers that can be vehicle mounted.  For ships, I would see lasers being mounted on smaller ships like Cyclones, LCS, and, possibly, the new frigate for use as anti-small boat and anti-drone weapons.  I don’t see the benefit of lasers with the noted target set on larger ships since they shouldn’t encounter those types of targets.

Disclaimer:  This is, by its nature, a highly technical topic in its underlying foundation and I am not a laser 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.