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On some computer games it is common to have a setting that disables friendly fire, it does not prevent shooting but it the bullets don't harm friend players.

In real life would it be possible to make a weapon (today or near future) that will never shoot someone from your own group?

Some sort of facial recognition would help but would need to work in milliseconds to lock the trigger and avoid the shot. But if the person is not directly facing the camera in the weapon or helmet it wouldn't work.

Next thought was related to some sort of GPS coordinates or team radio triangulation do determine if a person is from the team or not, but GPS is not that precise and I could only find articles on mobile phone triangulation based on cell towers that a bad precision as well.

Third thought was some sort of laser that would reflect from a special material in the teams clothing, it would block the trigger while you are targeting a good person. But depending on the angle the person is the laser would not reflect 180 degrees back to the weapon.

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    $\begingroup$ "Will never fire at a friendly", or "will never harm a friendly"? $\endgroup$
    – KEY_ABRADE
    Nov 8, 2021 at 23:23
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    $\begingroup$ Is this for a present day tech? Then this article should help: Identification friend or foe $\endgroup$
    – Alexander
    Nov 8, 2021 at 23:31
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    $\begingroup$ Simple: don't have friends. $\endgroup$
    – Schwern
    Nov 9, 2021 at 7:43
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    $\begingroup$ Just some food for thought. You will want a way to override the safety. Otherwise the next time a member of your military goes postal and starts wiping out his army base (using a civilian non-safety weapon), he will be utterly invulnerable to the weapons of his squadmates. $\endgroup$
    – PcMan
    Nov 9, 2021 at 8:18
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    $\begingroup$ A weapon that never shoots will never shoot a friend. And if everyone is your friend, you might not even notice :) $\endgroup$
    – bukwyrm
    Nov 9, 2021 at 9:27

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Out-there idea: Reverse-frangible bullets:

This isn't something invented yet, so it's a bit hypothetical. I imagine a team of armored SWAT or special-forces troops. Right before combat, everyone synchs a set of RFID transponders to the same frequency.

Their guns contain bullets that are frangible if they hit an armored target - as long as the tiny internal electromagnet isn't engaged. If the electromagnet is engaged, the projectile is held in an armor-piercing configuration designed to kill armored (or unarmored) opponents. Firing the gun activates the electromagnet, while proximity to the RFID signal of an ally deactivates it.

So a bullet set to the RFID signal of your squad deactivates and is frangible against the armor of an ally. At extremely close range, the electromagnet may not be active yet (or alternatively, it may activate and not deactivate in time) so point-blank ranges may be unpredictable. The projectiles would still pack a wallop, but you won't be blowing holes in a co-worker. Against unarmored opponents, I'd guess these bullets would still be lethal, so watch out for hostages and other soft targets. Any bullet that gets close to an ally will deactivate, so you don't want to be winging near-miss rounds past friends.

Obviously these rounds would take some very sensitive and advanced electronics not yet developed. The margin of error would be very tight. But I never believed they could invent frangible rounds, so why not invent the opposite? Who knows, maybe DARPA is making these things right now...

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  • $\begingroup$ This is a very interesting solution, thanks. $\endgroup$ Nov 9, 2021 at 2:33
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    $\begingroup$ A slightly less out-there variation would be bullets with a "bursting charge" designed to break them into fragments if they sense an ally in their forward cone. That way, instead of being shot, your ally is merely sandblasted by bullet dust. (This could still cause abrasions or eye damage; always wear your safety goggles, kids!) $\endgroup$
    – Cadence
    Nov 9, 2021 at 3:31
  • $\begingroup$ @Cadence Not a bad thought. There's a lot of cool possible engineering that can be imagined with frangible technology. Now if DARPA will just give me a security clearance... $\endgroup$
    – DWKraus
    Nov 9, 2021 at 4:09
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    $\begingroup$ Fellow members of Hydra: I present to you the ExterminaTron-2000. A 20mm armor-piercing autoturret, with a highly accurate directionfinder that will pinpoint any RFID signal within its zone of operation. Fully automated, it is completely harmless to Us, and to civilians. But when that SWAT team with their <snerk> "Safety Bullets" enter its field of fire.... Let's just say a mop and buckets will be needed. $\endgroup$
    – PcMan
    Nov 9, 2021 at 6:04
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    $\begingroup$ @PcMan Sure! Well, that and every improperly deactivated purchase, or by then possibly everything down to your coffee cup (which signals when it gets low so they can sell you more). But yes, every answer to a problem has a counter-solution. I was personally more worried about jammers meant to send out millions of different signals to make someone immune. But safety bullets are a super-niche market, since you can just use unmodified frangible bullets and kill routine unarmored terrorists. Without electromagnets, they still kill routine enemies and don't kill your armored guys. $\endgroup$
    – DWKraus
    Nov 9, 2021 at 12:18
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Genetically modify your own troops to be immune to the deadly poison with which you coat your weapon's tiny dart rounds. Then when friendly fire accidents occur, the victim will take no more harm than a mosquito bite. Meanwhile, your enemy who are not genetically modified to handle your poison will die as quickly as if they were hit by a high caliber round.

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    $\begingroup$ An antidote might make more sense, and require less tech. Even something simple, like narcan and a high-dosage opiate (allowing you to take prisoners, too, if desired). $\endgroup$
    – DWKraus
    Nov 9, 2021 at 1:55
  • $\begingroup$ An interesting idea, but narcan (as it stands) has a very short biological half-life; shorter than most opiates. This would need a narcan implantable slow-release device (already used for contraceptives, amongst others). But this would block most high-strength painkillers and anesthetics, without the device being removed first. Not nice when your buddy has taken a bullet to the arm. $\endgroup$
    – CSM
    Nov 9, 2021 at 10:04
  • $\begingroup$ @CSM I agree, narcan was just one idea. It could be set in an autoinjector so a tranquilized ally can trigger it themselves OR an implanted chip detects high tranquilizer levels and auto-triggers (but doesn't detect other opiates). You can use neurotoxin just as easily. There are antidotes to those as well. Of course, opponents can get antidotes as well, even to the stuff you are using with genetically modified troops. 20-40 years of genetics investment (growth included) foiled by an autoinjector and six months of traditional R&D. C'est la vie. $\endgroup$
    – DWKraus
    Nov 9, 2021 at 12:28
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Going in a little different direction from the rest of the answers, I propose a biochemical weapon.

Bullets cause physical damage, and without some really smart, quick acting, and extremely reliable technology, smart bullets would not be viable.

Instead, I propose a fast-acting neurotoxin in rounds that can pierce the skin without much damage. The entire team would be treated with an “antidote”/blocker/inhibitor of sorts.

Advantages

  • Enemies can’t use stolen technology on the battlefield. The technology would have to be reverse-engineered from scratch
  • Depending on the situation, the correct neurotoxin can be chosen to induce irritation, paralysis or death

Limitations

  • The ammo would have to be handled very careful during production and transportation, since anyone who hasn’t been treated with the antidote would get affected almost immediately.
  • Biochemical warfare research and production is banned by the UN.
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  • $\begingroup$ This seems the most realistic option, as it includes being able to shoot friends without (much) harm, thus circumventing the very valid points brought up by others around being unable to design a perfect system to avoid hitting them $\endgroup$
    – bytepusher
    Nov 10, 2021 at 2:29
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You can’t completely.

No matter what approach you take, there is some way to work around it or some dangerous failure path.

IFF tagging (mentioned by a number of other answers) can be fooled or hijacked (this has actually been an issue multiple times in the recent past).

A smart gun that only fires on identified foes can be hacked (and is still susceptible to the issues of IFF tagging).

‘Just don’t be where the bullets are going’ approaches assume intelligent troops, which is not something you should rely on (there’s a long standing joke about ‘military intelligence’ being an oxymoron, but even ignoring that stereotype mistakes can and will be made), and can just as easily be exploited by intelligent enemies.

Biological and chemical weapons have a nasty tendency to be completely indiscriminate and hard to defend against and there will generally be no way to perfectly protect your own troops (there is a reason that most of the smart militaries treated them as an absolute last resort even before they were banned by international treaty).

Even if you go really out-there sci-fi/fantasy and have omething that scans brain wave patterns, or looks at the target’s soul, or some other crazy evaluation of intrinsic properties of the target, there will probably be some way to spoof it (or some dangerous failure mode).

But even if you could, smart soldiers would not want to use it.

The issue here is that you’re introducing a couple of new ways for the weapon ti fail, no matter what weapon you are attaching this technology to, and intelligent soldiers do not like weapons that may fail to work. More specifically:

  • It might misidentify a friendly target as a hostile.
  • It might misidentify a hostile target as friendly.
  • It might just stop working completely and brick the weapon.

The first case is somewhat scary to any soldier who relies on this system, but the second and third cases are positively terrifying to any sane soldier. A weapon that may not work at when you need it to is, in most cases worse than no weapon at all, especially if the chance of failure is relatively low. This is because most people will, in the heat of the moment, assume the weapon will work, and thus usually put themselves in a dangerous situation when it does not work.

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Implant microchips in allied soldiers. Then, use smart guns with the same chip, and install integral microprocessors in them that use coordinate-based data to determine how far away the microchips in other allies are.

At that point, the distance can be processed along with the average accuracy/dispersion of the gun (perhaps multiplied by some factor in order to provide a safety margin), and a signal can be sent to automatically lock the trigger and/or firing mechanism if the gun is pointed within a certain number of degrees of a friendly.

It would depend on range; at point-blank, a person might take up, say, 90 degrees relative to the gun barrel, whereas they might take up 1 or 2 degrees farther away.

Note that there's no way to actually determine whether there's, say, a hill or a wall in the way of the friendly. This can result in situations where there's an enemy in front of you followed by three meters of concrete followed by a friendly - and the gun still won't let you shoot.

Also, the more components you put in something, the greater risk of failure there is.

Also, microchipping your soldiers might not go over well.

I still believe that it's better than most other solutions, though, because it allows you to fire essentially all of the time. The rate of "there's an enemy in front of a friendly, but the friendly would be safe if I missed, BUT IT STILL WON'T LET ME SHOOT GAH" would probably be lower than misfire rates.

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  • $\begingroup$ Good point about the person behind a person that could wrongly trigger the safety measure, thanks! $\endgroup$ Nov 9, 2021 at 2:36
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    $\begingroup$ Constantly broadcasting RF signals with position data (even if encrypted) sounds like a bad idea. The transponders in PcMan’s answer have the same problem. $\endgroup$
    – Michael
    Nov 9, 2021 at 10:26
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It is possible. You make a firearm that has the safety switch fuzed in the "safe" state.

The real challenge is to make a firearm that meets your "safe" criteria and still does the job well enough to be carried by your soldiers. Fundamentally, the "never" in "never shoot someone from your own group" is a damnably daunting threshold.

The reality of warfare is that if such a threshold can be achieved by machines, it typically isn't a place where warfare is undertaken. That's called "civilian life." Soldiers typically bring weapons into areas where life is not so simple. In the situation you describe, one would not sent valuable soldiers. Instead, you might send in a battalion of well armed Roombas to sort things out.

Practically speaking, the question would need to be re-asked in a very different structure. First, the premise needs to be questioned: why are we making a gun that can't fire on friends? Perhaps that sounds dumb and simple, but your actual goals may be better achieved by other means -- such as not engaging in warfare in the first place. Diplomats have rarely been implicated in the shootings of colleagues.

The second step would be to discuss acceptable failure rates. Something that is permitted to fail one-in-a-million gets designed decidedly different than something that is permitted to fail one-in-a-billion.

The third thing is to consider the enemy. Know thy enemy. If you are approaching combat as the ultra-technical eliete, opposing a bunch of farmers who know nothing about advanced weapons, you can solve some of the IFF issues in some ways. However, when fighting against a peer, they can take that IFF and use it to create guns that only fire upon their enemies.

With those in mind, you could start to craft ways to restrict friendly fire.

You didn't specify a technology level, but with present day technology the best solution we have come up with is to train the solder well, so that they point the firearm in the right direction, and only pull the trigger at the right time.

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    $\begingroup$ Thanks a lot, this really makes me want to throw away the original idea. You really have exposed several different aspects I didn't take into consideration. $\endgroup$ Nov 9, 2021 at 2:41
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Frame challenge:

A weapon that can't work both ways is a bad weapon.

It moves the responsibility both for shooting and for not shooting from the user to some hypotetical technology.

The technology can be hacked and no one will be responsible for its major failures (so it WILL be hacked).

Well, a soldier can be hacked, too, but at least soldiers can be held responsible for their actions.

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Step #1: Identify the Allies

Some basic IFF, it can be several encrypted radio emitters in the uniform of the infantry, or a real-time maintained registry of everything in the battlefield, updated by sensors in all the allied equipment, etc.

Step #2: Make a fired bullet don't harm

This is the hardest of all steps, because depending of what are you shooting it cannot be a way to avoid damage to a allied with a fired projectile. This projectile can be any particle or light, etc. IF you are using missiles you probably can the sames with smart bullets, but railguns, laser, neutrino beams, and many other there is no realistic way to avoid damage in a allied with a already fired bullet.

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  • $\begingroup$ I was not aware this is called IFF, the wikipedia article was useful. Thanks! $\endgroup$ Nov 9, 2021 at 2:34
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Trebuchets will shoot at targets with a very long range and the ammo comes from a high point. As long as your troops are smart enough to not be in the destruction path, tbey should be safe.

Arrows, too, should be safe with proper shooting discipline. Space your bowmen in lines with a safe distance from each other and have them fire volleys at 45 degrees or so upwards. Most european powers had mastered this by the middle ages. Again, this depends on your own people not being in the middle of an enemy army, so this is situational. I wouldn't have the slightest feeling of pity towards Leroy Jenkins, though.

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Your weapon is already in the enemy, you just need to activate it

Before the battle begins, the environment is filled with a swarm of nanobots containing botulinum toxin, sarin or some other highly deadly, fast acting toxin. Your people are already infected with a second kind of nanobot that transmits short range IFF codes to make your men immune to their effects, but everyone else is quickly contaminated as the nanobots are designed to tunnel through armor, ventilators, and concreate seeking out people to infect. While most toxins take a minimum of 1-5 minutes to kill, nanobots can kill much faster by carrying the toxins to the exact parts of your body in advance they need to get to making incapacitation and death just as instant as getting shot.

At this point you could just send out a giant radio signal commanding them to kill everyone, but such a weapon system could risk to many civilian lives, so when you can't just blanket kill everyone in an area, you follow up by sending in ground troops or drones with "guns" that are basically just remote controls used to confirm targets and activate the bots in your victims. This may still result in the occasional civilian casualties, but you can shoot your fellow soldiers all day long, and it won't matter because its just a low powered, directional radio signal.

The reason this works better than the smart bullet solutions is that the nanobots do not kill quickly upon exposure; so, your IFF does not need to make a split second choice under unfavorable conditions. But, it is also better than other toxin based answers because the time between a trigger being pulled and someone dyeing would be almost instant as opposed to several minutes.

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What you are asking for is a smart safety. As long as the system detects a friendly you can't operate the trigger.

The biggest issue I see in the system is how the signal or waves or the from of friendly identification is traveling from the soldier to the system. Because the friendly is sending the signal all the time in all directions.

Meaning that the system won't be able to distinguish between a friendly soldier behind you, beside you, or in front of you.

Once you start thinking about a system is not as simple as: signal on>safety on. Signal off >safety off. Then that thing is not mountable to a rifle.

I'm not scientists and I'm sure there are clever solutions. However the biggest issue is the parameters set and reality. Solving the problem only requires throwing more money and attaching a complicated back bag sized computer system.

For example imagine this "smart scope" but unlike it where it only needs to worry about calculations that relate to a trajectory of a bullet. It has to figure out if a friend or foe is in front of it.

This creates another complication and a point of failure. Whatever system or thing your soldiers use identify them as friends.

Lastly. This practically offers 0 advantages while potentially causing massive problems.

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    $\begingroup$ I understand that in a group of very well trained people they won't kill each other, but there may be situations of infiltrated/undercover people behind enemy lines. $\endgroup$ Nov 9, 2021 at 2:35
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It would absolutely be cool to have a thing like that. The problem is that how to do that. You know how in mini games they have that aiming cursor that moves when you turn. If there were glasses that simulate the world as a game, and it was linked to the gun and the brain, the gun might as well just use signals from the brain to signal when to shoot or not.

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  • $\begingroup$ Have you ever played such games with friendly fire turned ON? If so, you'll find that in a game, you won't have no friendly fire. It may even produce more than in real life - it's just a game, isn't it... $\endgroup$
    – bytepusher
    Nov 10, 2021 at 2:30
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The friendly would need to emit a "friendly" signal. Whether that's RFID, RF, motion capture balls, green-screen, or something else is up to you.

The gun needs to always be scanning for this signal and needs to have an internal "clutch" which engages and retracts accordingly. Soldiers are typically quite strong so if you try to implement a mechanism which locks their trigger then they will eventually break it. The trigger should always move freely and the internal clutch should be the one providing the pew-pew or no pew-pew.


All in all this is some great tunnel-visioned utopia but you'll curse the technology once a friendly decides to carry an non anti friendly-fire weapon and decides that you are the one that gets the pleasure of staring down the barrel.

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Easy, make so the weapon has some kind of infra-red laser that detects if it's an ally who's on the aim of the gun, if it's an ally it blocks the "fire" function.

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