In my RPG, an engineer is working on an energy weapon that kills enemy soldiers but leaves civilians and noncombatants untouched.

During the game, he takes the weapon designs and goes on the run, out of fear his superiors will find a way to 'corrupt' the technology toward more destructive ends.

Is there a possible way to make a weapon such as this work? Could it be perverted and if so, how?

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    $\begingroup$ have you tried googling it, because smart targeting is not a new idea. $\endgroup$
    – John
    Aug 19 at 23:59
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    $\begingroup$ How does your scientist propose to tell the difference between combatants and noncombatants? $\endgroup$
    – Cadence
    Aug 20 at 0:56
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    $\begingroup$ You're asking us to write your story for you here, and asking multiple questions. To reiterate the point made by @Cadence it doesn't matter if the weapon is a wooden club or a drone with a laser, there must be some measurable difference between soldiers and noncombatants. You need to decide whether that is cyberware, or a uniform or what. (You also seem to have some idea that discriminating targeting can be more destructive than indiscriminate targeting - not sure what you are thinking here.) $\endgroup$ Aug 20 at 1:40
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    $\begingroup$ That must be a very politically aware weapon. What is an enemy combatant and what is a friendly freedom fighter is a decision which is made in Washington, D.C., and does not rely on any observable attribute of the barbarian in question. For a well known example, in the 1980s the mujahideen of Afghanistan were friendly freedom fighters who fought against the evil Russians, and the U.S.A. even sent Silvester Stallone to help them; then things changed, and the exact same mujahideen became enemy combatants killing innocent American peace keepers. Moreover, the muj were never soldiers. $\endgroup$
    – AlexP
    Aug 20 at 3:59
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    $\begingroup$ One question at a time, also you need to give details like the technology level. $\endgroup$
    – John
    Aug 20 at 14:39

8 Answers 8


You need to target something that soldiers have and civillians don't.

There is this class-based, first person shooter videogame that I love very much, Team Fortress... Few people know its current iteration as a standalone game, but fewer yet remember the original version from the 90's. Back then one of the classes, the Engineer, had a weapon that was an EMP grenade.

When it detonates, anything explosive within the EMP grenade's blast radius will also blow up. That means other grenades being held by other players, bombs, and even shotgun shells due to the gunpowder in them. Enemy players caught in the blast with absolutely no ammo at all could shrug it off unharmed, but the more you were packing, the more it would bite. And you'd be left with only a melee weapon if you survived.

Your engineer could do something like that. An energy weapon that remotely detonates gunpowder and lithium-based batteries.

Civillians would either be unharmed or get some burns from the batteries in their smartphone and smartwatch blowing up. Hurts, but survivable.

But anyone carrying would have their weapon shoot even if the safety is on, and the remaining ammo would explode inside the clip. If you have a grenade or an RPG launcher on you, you'll be blown to bits.

And don't get me started if this hits a tank or any missile-carrying combat vehicle.

P.s.: as far as I know EMP's don't do that in real life. The game did a Rule of Cool with it when adding that effect. A real electromagnetic pulse might switch off or fry some electronics, but would not detonate explosives remotely.

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    $\begingroup$ I take it we're not allowed to talk about the fate of civvies with laptops, e-bikes, scooters... $\endgroup$ Aug 20 at 6:13
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    $\begingroup$ If we continue taking Team Fortress as an example, engineer's turret has smart targeting that avoid most friendly fire, and pyro's flamethrower can reflect dangerous projectiles back at bad guys without harming people otherwise. $\endgroup$
    – Tortliena
    Aug 20 at 7:32
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    $\begingroup$ @KerrAvon2055 we are, and those people would be hurt. This weapon could also turn a Tesla car into a big bomb. Food for thought. $\endgroup$ Aug 20 at 8:35
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    $\begingroup$ Also a fun excuse to get your soldiers using melee weapons! (Or crossbows.) $\endgroup$ Aug 20 at 16:19
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    $\begingroup$ @TheZouave this method is unrealistic and more like magic, so no. If it were realistic and could affect food, it would probably also affect living tissue just the same, so wouldn't be different from a very powerful laser. $\endgroup$ Aug 21 at 1:45

I think there is a simpler answer here:

The Weapon targets Body Armour

That is, in order for the Weapon to deliver a lethal effect on-target, it requires the person to be wearing Body Armour. You could do this different ways - some form of ray that causes Ceramic Armour to explode or something that causes metal armour to spall.

All the Soldiers are wearing armour, but almost all the civilians aren't (something something militia something plat carrier for bonus plot points).

So, why doesn't the enemy soldiers simply not wear armour then? Because without armour, they are much much much more vulnerable to all the other threats on the Battlefield that are more numerous than the new weapon.

How could it be perverted?

Well, Many of the materials used to build buildings (Metal and Clay Bricks) can be susceptible to the same effects by the energy beam. By changing the properties of the Ray slightly and increasing the power (by mounting it on a Vehicle) - you've made a weapon that is capable of levelling all the buildings in a town/city and crushing all the inhabitants in mere moments.

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    $\begingroup$ until it starts targeting civilian police. And many many soldiers do not were armor, especially militia and of course this does not stop you from accidentally shooting your own troops. $\endgroup$
    – John
    Aug 20 at 14:38
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    $\begingroup$ @John - I'm not so sure - if the Police are in uniform and openly carrying arms, they may be considered lawful combatants. $\endgroup$ Aug 21 at 1:42
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    $\begingroup$ I think they do this in clone wars with mandalorian Beskar $\endgroup$ Aug 21 at 3:50
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    $\begingroup$ "Soldier" is undecidable if you decide that SWAT are not soldiers but barely armed miliria are. $\endgroup$
    – alamar
    Aug 21 at 10:56
  • $\begingroup$ @JourneymanGeek It was in Rebels. starwars.fandom.com/wiki/Arc_Pulse_Generator $\endgroup$ Aug 21 at 17:01

First, there was IFF.

Your military fits their troops with short-range radio transmitters sending an encrypted signal. Ranged weapons (no matter the type) are fitted with directional receivers, and they will not fire if they are aimed at friendly signals. An improved version is not just blocking fire at 'invalid' targets, it actively aims at 'valid' targets and fires.

But the inevitable happens. The encryption gets hacked. Enemy troops mark themselves as immune.

So there is augmented recognition.

IFF codes are no longer sufficient. Optical recognition checks the shape of helmets and rifles. Spectrographic analysis of the materials of the uniforms. Perhaps even a biometric database of all friendly personnel in the area. Over time, cryptographic codes get less and less important, then they are dropped.

Genetic recognition

A breakthrough in a related field allows sensors to 'sniff' the genetic code of a person at short to medium distances. We are all dropping skin cells etc. all the time, so invent a means to analyze a single cell, with AI to match multiple 'positives' to wind patterns and to give a 'decent guess' as to the person this cell came from. Someone tells the military-industrial complex and the government that they can idenitfy ethnic origin from DNA with 'reasonable' accuracy. At least, the studies say, errors will be on the same order of magnitude as friendly fire by human operators.

Of course that does not just work on a battlefield. And not just for foreign ethnic groups. Your character thinks this through, gulps, and runs with all the prototypes.

  • $\begingroup$ "Enemy troops mark themselves as immune...." It is at this point that you program a code rotation to happen at hour H, with the weapons automatically targeting everyone who sent the old code. $\endgroup$
    – Ángel
    Aug 20 at 21:49
  • $\begingroup$ @Ángel, that's why I assumed a cyber-exploit instead of the capture of a transponder. With a hack in place, once the new keys and schedules get rolled out, the enemy listens. $\endgroup$
    – o.m.
    Aug 21 at 4:21
  • $\begingroup$ I saw some YouTube videos on the Phalanx close-in weapon system and found out it had no IFF. Why? Because if a missile is headed towards your position at mach 5 (or perhaps even 0.8 mach like a passenger jet might fly) there's no time for an IFF. The track of different objects on the radar are monitored for a potential collision with a friendly position and anything on a collision course is targeted. Friendly aircraft are given a "safe lane" where the Phalanx will not target in case they need to approach the position. With trial and error, or dumb luck, the enemy could find this safe lane. $\endgroup$
    – MacGuffin
    Aug 21 at 20:22
  • $\begingroup$ An Iraqi pilot shot down a plane after being sighted but was out of range of the AWACS so they didn't have permission to engage, as there were thousands of friendlies circling. - IFF +1; whether that's DNA or everyone has a chip, w/e. Your military-industrial complex is out of hand. "identify ethnic origin" wasn't on the docket.... Need to know if your name is on the roster. If we don't have your DNA or you've no chip... then I guess you're the 'enemy'. - Civilians are chipped. Get caught with a chip and it's the same as wearing the enemies' coat: you're a spy and you get put to death. $\endgroup$
    – Mazura
    Aug 23 at 3:08

Artificial Intelligence

It uses advanced and well-trained A.I. to tell the difference between friendly, enemy and non-combatant forces. It's an energy weapon so it can turn itself on and off faster than you could think, and the moment it detects itself pointed at a non-enemy, it turns off.

Can the A.I. be fooled? Of course! But humans could be fooled even more easily. But this weapon can tell the if the target is carrying a weapon - even a hidden one - or using it in a threatening manner, or can make a very good estimate of how long before the enemy pulls the trigger and who their intended target is, etc. to make a very well-informed decision on whether to shoot.

(After all, you probably might not want to kill even confirmed enemies indiscriminately anyway, just armed ones or ones who are a threat. e.g. you might want to give others the opportunity to surrender.)

It could also use facial recognition and have access to a vast database with info gathered from other intelligence sources (e.g. previous battlefield recordings, hacking enemy databases, spies, secretly gathered info on how the enemy identifies themselves to one another, etc.) to give even more certainty.

As for how it could be perverted, that would seem self-evident. Whoever got hold of it could reprogram it to target whoever they wanted! Not to mention gain access to the aforementioned databases...

  • $\begingroup$ This seems to be the obvious answer to me - and I feel like I've seen 'this technology goes wrong' a bunch of times in various sci-fi. Not that I'm saying it's bad - I'm saying there are various ways of doing it well. $\endgroup$
    – Joe
    Aug 22 at 18:42

It reads minds.

Okay, maybe not read minds but nearly so from whatever it can pick up off the person to indicate the state of mind. An aggressor will have a certain behavior, heart rate, breathing rate, odor (from sweat, armor, weapons, hormones, etc.), and/or perhaps even brain activity which can be more like actually reading the mind.

How could this be perverted? The aggressor soldiers learn how to control their emotions to not trigger the weapons. This would be difficult as there would be real fear, and going into battle without fear is a good way to get killed for lack of alertness and awareness. Perhaps some kind of drugs grants "immunity" from the weapons. Likewise the weapons could be fooled by friendly forces fearing these weapons, a vicious cycle since if the weapons screw up once then that instills fear in others which makes them fearful, etc. If noncombatants are taking certain prescription or recreational drugs, have some mental illness, are in a state of fear or some other mental state that is unrelated to the battle, then they could be inadvertently targeted.

Presumably the weapons could sense a state of surrender so that if the combatants turn and run, disarm themselves, or whatever might indicate they have become no more aggressive than a civilian, then the weapon ends any attack. Presumably the means to surrender to the machines would be told to as many people as possible, including civilians, friendly combatants, and aggressor combatants, so as to minimize any loss of life. Presumably this state of surrender would be made as instinctive as possible so that even those not told of the means to surrender would be expected to survive. People instinctively drop what they have in their hands and show open palms as one example of trying to show they are not a threat. Dropping to the ground with hands and arms over the head would be another example.

Advertising what triggers the weapons to stand down could be used against the machines. Aggressors told the means to surrender could use this to fool the machines, but a false surrender is a war crime which should discourage that. The weapons may stand down to a false surrender but the friendly combatants might not be so easily fooled, so each backs up the other to keep the aggressor combatants honest.

  • $\begingroup$ Exactly what I thought. The detection of brainwaves can be done by nanobots that are made to climb onto or into all people. $\endgroup$
    – Nav
    Aug 22 at 15:27
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    $\begingroup$ "OW, that was my foot you lumbering oaf, watch where you're go-BLAM" "Hostile intent detected. Enemy combatant neutralized." $\endgroup$
    – Shadur
    Aug 23 at 7:33

Your soldiers are chipped

As long as soldiers and civilians are both human, your story has to create the discriminator. So your military is required to wear/be implanted with some sort of ID chip.

Your soldiers are augmented

Military personnelle are required to undergo augmentation when they join. This medical regimen has a side effect of creating certain hormones or pigments that let off a particular smell or leave them with a certain skin characteristic. Perhaps their skin reflects UV light (maybe the military required this to protect the soldiers from UV exposure during space operations). The weapon then relies on ion sensors for smell, or UV targeting lasers.

Theoretically, AI could be used to allow a weapon to discriminate between military and civilian personnel if it were allowed access to sensors for the above modifications. However, there are a number of challenges before this could be done reliably.

  1. AI systems are trained on data that can introduce bias. For example, if the data is mostly images of male soldiers, then the AI system may be more likely to misidentify a female soldier as a civilian.

  2. The context of a situation won’t likely be understood. For example, a civilian wearing a military uniform may be mistaken for a soldier.

If you want the weapon to do all the discrimination itself without a world-based characteristic, even detecting military out of uniform and under cover, then magic is your only choice. There is no scientific way to look at two people and know which one signed a contract.

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    $\begingroup$ The point of a weapon is to kill enemy fighters, not your own soldiers. You cannot impose any requirements on the enemy; that is why he is called the enemy. You may recall that quite recently the U.S.A., the world's sole remaining superpower, lost a long war in Afghanistan, where the enemy fighters did not wear uniforms, were not even soldiers in any meaningful understanding of the word, and surely did not wear any identification marks. $\endgroup$
    – AlexP
    Aug 20 at 4:06
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    $\begingroup$ why would enemy soldiers chip themselves as "soldiers" ? $\endgroup$
    – user104995
    Aug 20 at 10:00
  • $\begingroup$ @AlexP it’s not my job to write the story as to why the enemy chose to chip their soldiers. I do not pretend to assume anything about what any party chose to do to another party. A discriminating weapon that homes in on the enemy’s chipped soldiers is an answer to the question. That was what was asked. Whoever is writing the story is responsible for explaining why they chose to put the chips in their soldiers. I’m sure there are many many very good reasons why a specific, communist army or capitalist army would choose to chip their soldiers. There’s a world of story reasons this could happen. $\endgroup$
    – Vogon Poet
    Aug 20 at 14:05
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    $\begingroup$ so metal gear 4? Nanomachines son! $\endgroup$
    – John
    Aug 20 at 14:40

Don't shoot at smartphones

Your military has excellent electromagnetic radiation detectors, quickly pinpointing and tracking any signal source. Therefore, soldiers are forbidden from carrying any continuously-transmitting wireless device, to not reveal their location and movements.

Knowing this, the weapon tracks sources that look like civilian devices (smartphones, wireless headphones, car keyfobs), which nowadays is virtually everyone, and refuses to shoot in that direction. The detectors are good enough to tell if the signal is directly in line of sight or if it's a bounce, so soldiers can fight in urban environments without too many problems.

Of course enemies combatants will try to abuse this system by broadcasting "civilian" signals in the middle of combat. There are two defenses against that:

  • The weapon has thresholds for normal behavior, including rate of movement and how long the source must have been active. Turning a smartphone on during the firefight will not help.

  • Pretending to be a civilian is against the Geneva conventions and severely punished.

You can also add drama to your story in the form of a civilian with a dead smartphone caught in a firefight, or a soldier miraculously saved by a smartphone left behind.


AI identification of friends and foes is the most likely and most realistic candidate

Really, the most realistic way to achieve that is to help soldiers identify targets before they manually shoot them with conventional weapons.

AI could be used to identify friends and foes. We've made enough progress with AI that it's not unconceivable to have a well-trained AI model that can interpret what the soldier sees and paint targets.

Displaying the information would be fairly trivial, and we have already plenty of examples of what that would look like if you've ever played a shooter in the last decade.

The next technological leap would be to link IFF to the trigger of the guns, forbiding it to shoot non-friendlies (excluding civilians), maybe even non-hostiles (including civilians). Then the next step would be systems that can point at a target autonomously, and either fire at will or fire on command.

Mistakes will still happen, and it's not some kind of smart bomb that kill all baddies in a city leaving everybody else alive. But on the bright side, it also doesn't shoot your own guys, which is something a smart bomb would have trouble achieving.

This supposes the enemy follows the laws and customs of war, which includes showing your true colours (i.e. wearing an identifiable uniform of your own faction, and bearing arms clearly). Not because not doing so would be a war crime (which it is, but that's only a problem if you lose), but because that's a good way to trick your own troops into shooting themselves.

That covers what the technology could be. We'll cover how it can be perverted, but before we get there I need to say two things.

It doesn't need to be a working weapon

"An engineer is working on an energy weapon" doesn't mean there is a fully working prototype yet, let alone a production version. It might work in a lab under ideal conditions, but hasn't been field-tested. As such, it may have flaws to be resolved that makes it good enough for paintball but not enough to be deployed. And certainly enough to envision its limitations and all the ways it can be perverted.

In fact, it doesn't need to be a weapon. Technology can be designed for non-combat purposes, only to be coopted by the military to shoot at people. Or seemingly innocent technology being funded by the military to make it easier to shoot at people.

There are precedents for that. The Silicon Valley first thrived on US government contracts, being both the biggest financer and biggest client of early electronics. Why? Well to make better targeting systems for missiles. GPS famously is US military technology. Encryption was once classified as a weapon. You'd be amazed the amount of technology in your pocket that owe its existence to the military-industrial complex.

So it's entirely possible for your "weapon" to be a new form of AI training, some fundamental research on a new physical phenomenon that happens to make grenades explode randomly, or some other seemingly innocent prototype.

It may or may not work as advertised, but it doesn't matter too much because...

Never underestimate the magic thinking of generals

It would be very easy for generals to consider the weapon works exactly as described this far: a perfect weapon that only kill the people you want dead and not anybody else. After spending billions of moneys into it, they'd be right to expect that it should work as advertised. And they might even convince themselves that it does, at least until they start using it and realise it doesn't really.

It would also be very easy for generals to consider that anybody that the weapons kill was an intended and justified target. The obvious example here is "strategic" bombing. You level whole cities, and it's not terror bombing because it's totally justified, you're only shooting at the military, or its support industries, or whomever works for those support industries, or whomever supports those who support them.

Whatever helps them sleep at night, or not look like monsters after the war is over.

For the engineer however, it should be obvious how the "weapon" can be used and abused.

No matter how it works, the engineer should be scared of it

The idea of a weapon that can be targeted against a specific group of people is frightening. Today you're shooting enemy soldiers, tomorrow you might be shooting at protesters, and the day after that at ethnic minorities. All horrific prospects for people with a conscience.

And those concerns are very justified with AI models. AI doesn't erase societal biases, quite on the contrary. It is near impossible to remove biases in training, and there are a lot of them in our data. It would be quite easy to imagine an AI trained to shoot at Middle Eastern soldiers and not your own majoritarily white troops, that ends up shooting anybody with dark skin regardless of the uniform or lack thereof.

It doesn't really matters how it works, or if it works. The simple fact that it might one day work should be enough for the engineer to want to scrap it, and enough for the powers-that-be to want it.


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