The problem: If somebody fires a (kinetic) gun on a spaceship, the bullet is likely to penetrate the hull and cause a host of problems.

I want to incorporate spaceships and fighting on them and in them, boarding action and all the other fun stuff in my current project. How could you solve this?

  • From my other questions and my extensive research I know that it is very probable that kinetic guns (chemical propellant and other) are likely to keep the #1 position in handheld firearms. For example, lasers can easily be nullified by reflective armor. Is that right? In this case, no energy weapons please.
  • The scenario is low-AI, too. So no thinking or 'intelligent' bullets.
  • I once found an idea about a material within the ship's hull which 'deactivates bullets'. But just build a body armor out of it, and you’re bulletproof.
  • Tasers and the like are OK for law enforcement etc. But I plan to incorporate vicious and deadly conflict within a spaceship.

So, is there any solution, or do I need to get rid of one or more of these requirements?

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    $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – Serban Tanasa Oct 12 '16 at 21:22
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    $\begingroup$ Just a quick point re your negation of bullet-proof material - just because the material is available for ship manufacturers to use to protect the hull doesn't mean it's practical, economical, or even generally available, for use in the manufacture of bullet-proof vests. Besides, we already have bullet-proof vests, but people don't always wear them. $\endgroup$ – megaflop Oct 13 '16 at 12:27
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    $\begingroup$ Watch Firefly... $\endgroup$ – J... Oct 13 '16 at 16:59
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    $\begingroup$ Carry needle guns that fire fletchettes? you might fit a thousand needles in the space of 10 bullets, giving a hundred 10-needle shots or ten 100 needle blasts. 10 or 100 needles moving fast will injure or kill a human, but won't have the same kinetic impact on solid walls. Vaguely like a shotgun, but could be electrically launched. $\endgroup$ – Criggie Dec 21 '16 at 3:17
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    $\begingroup$ See also Have spaceships been tested to withstand bullets? on Space Exploration. $\endgroup$ – a CVn Apr 21 '17 at 14:55

31 Answers 31


Bullet holes are not as bad as you think. The ISS would take over 7 hours to depressurize through a bullet hole.


Even a few bullet holes still gives you plenty of time to react.

In a worse scenario of someone setting off a hand grenade or something that punches a very large hole, humans can still remain conscious in a vacuum for up to 30 seconds, maybe enough time to exit the room and initiate some emergency door sealing or cabin repressurization.

Speaking of repressurization, you might have emergency air-replacing equipment to replace air being lost through bullet holes. The capacity of this equipment can be left to your imagination (might be fun to emergency replace massive quantities of air with boiling oxygen directly from the liquid oxygen fuel tanks into the environment system. This could retain pressure for a very long time, but introduce major fire risks (plus pure oxygen at high pressure is poisonous; pressure needs to be kept at a reasonable low. A safety system would regulate this).

But wait a sec, can a bullet even puncture a spaceship hull?

Our current micrometeorite shielding can protect against the energies of bullets at point blank range, by several times. An aluminium slug of 7mm at 7kms can be stopped by whipple shields. That's a kinetic energy of ~36kJ. A handgun bullet at point blank range is more like ~8kJ. (http://calhoun.nps.edu/bitstream/handle/10945/1233/04Dec_Kalinski.pdf?sequence=1) The whipple shield is composed of an outer bumper layer, which fragments the projectile before it hits the hull, so is directional and assuming that projectiles are coming from outside (how naive!). So maybe it's not impossible to puncture the hull from the inside out with high powered weapons. But keep in mind this is using current day shielding technology too, and not the new fancy self-healing hulls which are being worked on. Perhaps micrometeorite shielding is more advanced on the OPs interplanetary spacecraft, making onboard gunfire safe, in a depressurization risk sense :)

I'm not sure anyone, including the shooter, wants to be in a small, metal, possibly bulletproof can while firing off high velocity rounds. The more bulletproof you make the hull, the less you'd want to use guns inside. So I guess it's plausible that lower powered guns would be more popular, just to avoid ricochets.

Finally, if you're about to be boarded, it'd be a smart idea to suit up beforehand. An assault tactic wouldn't be limited to bullets, it'd likely involve punching holes in the enemy vessel with cannon prior to boarding (just like old pirate ship battles, yarr!)

  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – Serban Tanasa Oct 14 '16 at 22:51
  • $\begingroup$ Additionally, a bit of cardboard and duct tape will be a good temporary fix to keep the air in. Your chief worry, however, from punctures is not the loss of air, but damage to any power lines or ducting that lies between the interior and exterior walls. $\endgroup$ – EvilSnack Oct 15 '16 at 5:02
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    $\begingroup$ Micrometeorite shielding is on the outside of the vessel. It's not even a part of the pressure hull. At best you could say that a bullet fired from inside the pressure hull, if it were to escape the vessel, might be blocked by that vessel's micrometeorite shielding before it could damage another vessel. $\endgroup$ – Beanluc Oct 15 '16 at 18:13
  • $\begingroup$ I think it might be interesting to note that, for a while, the Soyuz emergency landing survival kit included a gun: spectrum.ieee.org/tech-talk/aerospace/space-flight/… (Wiki: "TP-82 Cosmonaut survival pistol") $\endgroup$ – stux Nov 22 '18 at 17:28

What you are looking for has been around a long time. Check out Glaser Safety Slugs. They were designed to not overpenetrate and

The United States Federal Air Marshal Service tested and used the Glaser Safety Slug extensively in the 1970s and 80s on board commercial passenger aircraft to defend against hijackers.

The bullet design

... has a core of very tightly packed lead pellets. On impact, the bullet fractures along manufactured stress lines in the jacket—imparting all the bullet's energy very quickly rather than over-penetrating a target or ricocheting on a miss.

enter image description here

They are also used in home defense weapons as they are not supposed to penetrate the home walls endangering someone in the next room.

  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – Serban Tanasa Oct 13 '16 at 13:36
  • $\begingroup$ The problem with this idea is 1) the boarders probably aren't going to bother using these unless they want to capture the ship for their own use, and 2) personal armor will likely be pretty good at preventing the bullet from "overpenetrating" through itself and into its wearer, rendering them all but useless to a defender. $\endgroup$ – Doktor J Oct 13 '16 at 20:32
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    $\begingroup$ Read up on Glaser if you use this idea. Their main downside is that they are crazy lethal. One comment about them says that 90% of people shot with hand-held pistols survive, but 90% of the people shot with Glaser have died. $\endgroup$ – Tom Nov 27 '16 at 7:36
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    $\begingroup$ The concept of a "safety bullet" is a great example of an oxymoron. $\endgroup$ – Criggie Dec 21 '16 at 3:11

The short answer is that if you are wearing armor which matches or exceeds the ability of the interior hull to resist punctures, then projectiles which use that characteristic to cause damage will be obsolete in proportion to the availability of that armor.

Weak points with the armor are likely to be exploited, and these are likely to be combined with attempts to cripple the effectiveness of that armor. E.g. gases which are absorbed by skin, plasma bolts like the PPGs of Babylon 5, and short-range grapping.

Here's some parallel thinking which might help the situation: To injure a human body, you need only penetrate it once. To minimize loss of air through a hull, you need to seal any punctures soon following their occurance. Perhaps railguns with miniascule slugs, a hull material that does not allow tears to propagate, and a special system that secretes sealant much like is used in some tires.

Of course, and such sealant would need to harden very rapidly and have some method of delivery which was quite tolerant of the repeated perforation which you are administering to the hull of your vessel.

If one would consider hull design as a possible answer to this question, then I would recommend

  1. an inner covering of fluid epoxy which hardens in a thin, amorphous film on exposure to nitrogen or whatever comprises the air spaces in your vessels. The activating agent does not penetrate deep in to this tar.
  2. a layer which supports the tar, allowing the projectile to penetrate rather than attempt to absorb or convert its energy — doing so might create progagating cracks which would create catastrophic failures, depending on how you built your pressure hull.

This system would, of course, require diligent maintenance and repairs between and during battles.

Please note that I do not take any of the following into consideration, as they were beyond the scope of my answer — granted, some of these concessions are more justifiable than others:

  • Why you would be shooting weapons onboard the ship, and not killing the crew from the outside e.g. by crippling the engines and life-support systems.
  • Whether the ballistics actually caused a path of airflow from the interior to the Void outside.
  • Whether the pressure hull would be integral with whatever system of micro-meteorite shielded existed on the outside.
  • The nature of the shielding and weight considerations. Keep in mind, however, that heavier armor makes for heavier ships, which makes them less maneuverable and more costly to fuel. Unless, of course, you were using some zero-point technology, but that is well beyond scope of question.
  • Where you'd put support systems, and how you'd be protecting or repairing those in the event of a ballistic casualty. This one is really an important, but not considered in the question.

Remember, also, that even if you were using plasma bolts and chemical weapons to subdue invaders or crew, there's always the need to plan for explosive substances within the pressure hull.

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    $\begingroup$ Self repairing hulls will be common technology to protect against micrometorite strikes long before the need to protect against bullets arises. $\endgroup$ – Innovine Oct 11 '16 at 6:19
  • $\begingroup$ Why would one have a hull that invites people to shoot aboard the ship? $\endgroup$ – Three Diag Oct 11 '16 at 15:16
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    $\begingroup$ It is probably not going to be easy to wear armor as hard as the ship's on a person. In most senarios, the Hull is going to be far stronger than any armor a person can wear, simply because it needs to be strong. If your wearing armor that strong, its going to be Plate armor, which will have very huge flaws with it, such as weight/bulk, and the weak points will be easily exploitable. $\endgroup$ – Ryan Oct 11 '16 at 16:06

I think any spaceship with a hull capable of surviving interstellar travel would have no problem surviving a tiny little anti-personnel bullet. So if you're going to have relativistic or FTL spaceships, I wouldn't worry about bullets penetrating the hull (though internal damage, like "oh man, the food replicator took a hit, hydroponics needs to work double shifts to keep us going" could make for good plot developments).

Battle-hardened ships will have tough enough armor to survive ship-to-ship weapons. So, like FTL ships, they'll have little trouble with small-arms fire.

Even a short-range, light-duty spaceship isn't going to suddenly explode just because someone put a little hole in the hull. Pirates and military ships will likely have spare metal and welding tools to repair the worst of the damage, and compressed air or solid materials that can be evaporated into a new atmosphere.

All but the most hardened civilian spacecraft will likely be easy prey for pirates and military ships alike. Since firearms aren't going to help much anyways, they'll be generally prohibited for anyone except (maybe) security teams.

Similar logic should apply to space stations. Civilian stations will be cheaper and more fragile, and firearms (or anything else that could punch holes in things) will be prohibited. Military stations, pirates, and corporate headquarters will tend to be hardened a lot more, allowing for more brutal, savage firefights without suffocating everyone on board.

Of course, there will also be safety systems, like auto-sealing doors, vents, and ducts, that kick in when a room starts depressurizing, regardless of the type of ship/station involved. So small-scale firefights won't be the end of the story, even for civilian ships.

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    $\begingroup$ anti-meteorite shilelding tends to be outside, and fights happen inside. Isn't this a problem? $\endgroup$ – Mołot Oct 11 '16 at 6:33
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    $\begingroup$ @Mołot: I can imagine circumstances where the shielding isn't air-tight (like, it's a few meters from the actual hull, with gaps here and there). But as long as the shielding is air-tight, and close to the hull, the bullet will penetrate the hull then stop on the shielding. A little air might escape into the gap (if the shielding isn't pressed onto the hull), but that's it. $\endgroup$ – MichaelS Oct 11 '16 at 6:51
  • $\begingroup$ @Mołot Presumably a hole has to go all the way through the hull to be a problem. So whether the inside is tough of the outside is tough, so what? Wll, if there's wiring or plumbing or whatever sort inside the walls, a shot that penetrates the interior wall could damage this, but that's a different category of problem. $\endgroup$ – Jay Oct 11 '16 at 14:22
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    $\begingroup$ This is very true. Look at modern day ships/boats. The Navy isn't worried about a warship being sunk by small arms fire from a boarding party, because ship hulls are made out of hard metals like steel, while bullets are made out of soft lead. Even without armor, it's not much of a problem, because lead bullets have very low penetration into hard metals, and you're probably going to have thick enough hulls that a bullet isn't going to get through. $\endgroup$ – HopelessN00b Oct 11 '16 at 14:47
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    $\begingroup$ @Mołot That's the answer to why a sci-fi future with space stations and space fleets and interstellar travel and sexy alien women isn't realistic and won't happen, not the answer to how things would be if we ignore the inconvenient parts of reality that we need to in order to make such a future possible. $\endgroup$ – HopelessN00b Oct 11 '16 at 15:02

I don't think you solve this problem.

If I'm attacking your people on your ship, then I'm already in a space suit. I just use a grenade or shaped charge and blow holes in your hull.

Then, I go in and kill anybody (the few) who managed to get into a suit fast enough.

Eject corpses, patch holes, re-air from the reserve air tanks that your ship has (possibly augmented with air from tanks I brought.)

Any defense against bullets just causes your opponents to up the ante and use something more powerful.


One thing you're overlooking is that you don't have to put a hole in someones armor to kill or wound them - the impact of a standard rifle round is more than enough to break ribs, even if you're wearing a trauma plate. A .50 BMG or other heavy ammunition will probably outright kill you from the internal injuries, even if your armor somehow prevents the bullet from penetrating.

The frangible rounds that User2448131 mentioned are a good place to start. A large, slow, soft bullet will pack huge amounts of kinetic energy with limited penetrating power. Instead of punching holes in enemy armor, deliver rib-breaking, internal-organ rupturing concussive impacts to their bodies. You have to remember that an armored suit still has soft, squshy meat on the inside.

Ironically, severely injuring your enemy without punching holes in them offers a lot of advantages. You can't pressure a dead man into giving up information, but you can pretty easily coax it out of someone with 13 broken ribs and a ruptured spleen by promising them medical attention. It also means you can have more elite soldiers, since they're more likely to be injured & incapacitated than outright killed.


Firearms are a pretty big risk on spaceships, but not because they're going to punch holes in the hull. A bullet-sized hole in your hull is the least of your problem in a situation where boarders have gotten on your ship, if it can get through an armored hull at all. In an ideal situation, each room has spare space-suits for those inside in case of emergency as well as your crew having their own space-suits so hull breaches are not that big of a deal.
If you get in a combat situation, the first thing anyone's going to do is suit up. Venting atmosphere in a situation where your entire crew is wearing suits is annoying but not life-threatening. What's a lot more dangerous about firearms is that they produce heat and small explosions to propel their projectiles. Metal bullets also tend to spark when they hit other metal so firing guns as we know them is going to have an increased risk of fire (which is a BIG problem on a spaceship).
Another consideration is ricochets. Spaceships are tiny cramped things, most of the time with corridors that are maybe 1 or 2 persons wide, depending on how important they are. If you fire a bullet in there and you miss, it's going to go all over the place. Best case scenario, it glances off a plate somewhere and embeds itself in a locker or something. Worst case scenario, your round shatters against something hard and you have shards of hot metal going everywhere. You might consider this to be a bonus as it makes your guns more lethal but remember that if you need to cross a bit of vacuum and there's a leak in your suit, you're going to have a bad time.
Finally, there's recoil to consider. We all know newton's third law and in a zero-G or near zero-G situation, firing bullets does funny things. You shoot a gun while floating and the bullet's going to go one way and you're going to go the other way, making aiming in sustained firefights a bit of a hassle.

Long story short: shooting firearms in a spaceship isn't a great idea but it's not immediately lethal if you miss. Depending on how ruthless you want to go, maybe boarding actions are fought mostly with melee weapons. Given that guns are problematic, maybe only the most hardened or crazy or high-tech crews use them. So most of the grunts that board ships show up with clubs, swords and other crazy shenanigans. If you want brutal close quarters combat, you can't do much better than high tech swords.


Assuming a hostile force is boarding your spacecraft, you probably have more issues than a few stray rounds going through the life support volume. The hull may well have been breached by the enemy spaceship overwhelming your ship's defences using high energy lasers, railguns, missiles and nuclear explosives, and then there are the holes punched in the hull so the Marines or boarding party can get inside (they will want to enter at multiple points to overwhelm your defenders).

However, they are still trying to fight in a relatively confined 3D space, so there are some analogies to a current naval boarding party. The borders will need compact weapons capable of putting down a high amount of firepower if needed, so weapons similar to today's submachine guns and carabines will most likely be the primary weapons carried by the troops. Secondary weapons will be shotguns and grenade launchers, with pistols as close range backups. Boarders will also carry breaching charges and engineering tools to penetrate bulkheads to clear the entire ship.

enter image description here

Royal Canadian Navy Boarding Party

enter image description here

MILCOR grenade launcher. Nothing like a lot of overwhelming firepower when you need it

Weapons will have to be different from the ones carried on Earth, since recoil forces will throw the shooters off if they're fighting in a 0 G environment, so expect large muzzle devices to redirect gasses and the stocks to be quite large to accommodate recoil compensation devices (imagine the working parts or the weapon in a cradle inside the stock).

As for the damage to the ship's hull, using safety rounds and shotgun pellets will limit the damage, but consider that hulls will be much tougher than you think. Airplane hulls do not disintegrate under small arms fire, and inflatable structures like the Bigelow space habitat module are made of multiple layers of Kevlar, so resemble a bulletproof vest more than a fabric balloon. A metal and composite spacecraft will probably be a reinforced structure like in the illustration to combine strength with light weight, so damage will not propagate through the hull.

enter image description here

If you look at sites which discuss space warfare, like Atomic Rockets or Tough SF, you will see the speeds and energies being deployed make boarding rather unlikely. I might consider rethinking the action to something like customs agents or police boarding a docked spacecraft to make the setup work.

  • $\begingroup$ I think one problem here is that if spaceship hulls are tough, bullets are likely to ricochet, with a real probability of any misses hitting the shooter (or innocent bystanders, hostages, critical equipment, &c). It might be more realistic to use swords/knives. $\endgroup$ – jamesqf Oct 11 '16 at 4:38
  • $\begingroup$ Awesome answer! I already have a solution to the speed/energy problem :) I just let all the action play in a tightly packed asteroid megacloud. $\endgroup$ – openend Oct 11 '16 at 11:45
  • $\begingroup$ Saftey slugs, shotgun pellets and even grenade fragments will lose energy quite quickly upon striking a target or a wall, so ricochets are only going to be a minor issue in this setting. $\endgroup$ – Thucydides Oct 12 '16 at 15:16



The typical use of a shotgun is against small and fast moving targets, often while in the air. The spreading of the shot allows the user to point the shotgun close to the target, rather than having to aim precisely as in the case of a single projectile. The disadvantages of shot are limited range and limited penetration of the shot, which is why shotguns are used at short ranges, and typically against smaller targets. Larger shot sizes, up to the extreme case of the single projectile slug load, result in increased penetration, but at the expense of fewer projectiles and lower probability of hitting the target.

Aside from the most common use against small, fast moving targets, the shotgun has several advantages when used against still targets. First, it has enormous stopping power at short range, more than nearly all handguns and many rifles. Though many believe the shotgun is a great firearm for inexperienced shooters, the truth is, at close range, the spread of shot is not very large at all, and competency in aiming is still required. A typical self-defense load of buckshot contains 8-27 large lead pellets, resulting in many wound tracks in the target. Also, unlike a fully jacketed rifle bullet, each pellet of shot is less likely to penetrate walls and hit bystanders.[2] It is favored by law enforcement for its low penetration and high stopping power.

On the other hand, the hit potential of a defensive shotgun is often overstated. The typical defensive shot is taken at very close ranges, at which the shot charge expands no more than a few centimeters.[2] This means the shotgun must still be aimed at the target with some care. Balancing this is the fact that shot spreads further upon entering the target, and the multiple wound channels of a defensive load are far more likely to produce a disabling wound than a rifle or handgun.[3]

In a space ship, the shotgun would have the following advantages:

  • Very high stopping power at the short ranges of an interior environment
  • Low potential to penetrate the hull of the ship
  • Low potential for friendly fire due to overpenetration, especially nice for the initial boarding process when friendlies greatly outnumber enemies
  • Small drone enemies that could be employed in a sci-fi setting will be easier to hit than with rifles or handguns, though this effect would be greater in a more open environment

Don't kill. Incapacitate.

Rather than trying to penetrate the enemy's Armour, you fire sticky foam, either in a stream, or in large grenade like gelcaps at the target. You reduce their ability to move, gum up their weapons and the worst you'd need to handle the aftermath is the space janitor corps armed with solvents and whatever moplike thing you use in space.

You can crack them out of their armour at leisure after you've left them to stew for a bit.

  • $\begingroup$ The sticky foam could also double as a means to patch holes in the hull of your spacecraft. $\endgroup$ – Justin Ohms Oct 11 '16 at 21:31
  • $\begingroup$ So the character of Viscera Cleanup Detail might actually have a purpose ? $\endgroup$ – Goufalite Oct 12 '16 at 9:23
  • $\begingroup$ Those folks are the real heros. $\endgroup$ – Journeyman Geek Oct 12 '16 at 9:24
  • $\begingroup$ It's nice to be nice. Everyone be nice. $\endgroup$ – Wossname Oct 15 '16 at 11:39

Chemical weapons that incapacitate humans but don’t breach the hull, maybe delivered by needlegun? Hulls thicker than any feasible armor? Aimbots that minimize the number of stray bullets? Self-repairing hulls or fast auto-repairs?

  • $\begingroup$ If the people on the spaceship weren't expecting to be boarded by people with chemical weapons, then they probably won't be stocked with gas masks to defend against it. If they jump into space suits to have a contained air supply and protect their skin/eyes that isn't vulnerable to poison gasses, there are more caustic ones that will eat right through the suits (and surrounding ship, and you), such as fluorine based clouds of gas. Chemists are (rightfully) afraid of working with these kinds of compounds. $\endgroup$ – Cody Oct 11 '16 at 18:08

Assuming an advanced metallurgy culture a solution is to have small bullets, flechettes , or sprays that react violently with water. Think of type of hyper-sodium (note how normal sodium reacts with water)

Projectile weapon: A projectile that only explodes if hits H2O. Small hole (flechette) in hull may not be an immediate problem and could penetrate any armour.

Human target flame-thrower: Generate high velocity shaped mist of reactive particles. People will burst into flames, but at the normal spaceship humidity levels the stream is not hot enough or projected long enough to damage equipment. Particle size and rate can be adjusted not to damage spaceship skin. Personal armour would need to be both all enveloping and quite tough.

Fluid based: Seep through armour. But waterproof suit would block.

Clearly this kind of weapon could be a problem if accidentally shoot the spaceship's water supply - but how much "bang" do you need to stop a person? and water does dampen kinetic energy effectively.


I had another idea - a gun that fires 2 dissimilar pellets that are connected by an explosive string. The pellets are fired in such a way that they spread out in the air and draw the explosive string taught between them. When this projectile hits an object, it wraps around it, in a similar way to a Bola.

When the projectile wraps itself around a victim or object, the ends will curl around it, and the centrifugal force will make them whip around and hit the object with enough force to detonate a fuse which ignites the explosive string.

It will do maximum damage to an object it wraps around, thus it shouldn't do a great deal of damage to walls or hull of the spaceship as it will hit the loosely. However, once wrapped around a person, it would wrap rightly around them, explode and should shred them, or at least crack their armour and shock them.


Just make your ship hulls out of a relatively soft metal like lead, but make it extremely thick. If your story's technology allows for high velocity armor piersing rounds which can penetrate N feet of hull, make your hulls 10 N feet thick.

The softness of the hull walls should reduce richoettes while the thickness lessens the chance of leaks.

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    $\begingroup$ That just makes your ship very heavy, which translates to unacceptable fuel consumption and shortened range. $\endgroup$ – Innovine Oct 11 '16 at 6:21
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    $\begingroup$ @Criggie it was "like lead" not "exactly lead" $\endgroup$ – Magic-Mouse Oct 11 '16 at 10:53
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    $\begingroup$ I didn't realize that ships had to be able to land, nor that energy consumption was a major issue. I figure that a heavy ship would have some advantages in a culture which uses planetary gravity wells for their navigation and acceleration/deceleration processes. $\endgroup$ – Henry Taylor Oct 11 '16 at 13:23
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    $\begingroup$ Easier to hollow out an asteroid in that case $\endgroup$ – Innovine Oct 11 '16 at 15:25
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    $\begingroup$ Use kevlar instead of a metal and line it on the inside with about an inch of tar and a coat it in rubber? rather then metal. $\endgroup$ – Tomy-rex Oct 13 '16 at 16:30

Why not just make the hull bulletproof? It probably has to be anyway to survive the super-high speed grains of space pebbles whizzing about... As to why they don't just make body armour out of the same stuff? Simple: it's too heavy or has to be too thick to wear. Even if they do, body armour has moving parts and therefore chinks.

Or, the ship has an automated system that can quickly plug/patch small holes in the hull.

  • $\begingroup$ Arrow may penetrate bullet proof glass. Projectile speed and mass matters. $\endgroup$ – MolbOrg Oct 12 '16 at 19:13

What about fixing the guns instead of the bullets? We have guns with cameras that you can hold the trigger down and they won't fire until an IR signature passes over the cross hairs. As long as the bullets don't over-penetrate, the ship should be safe. There's a little AI there, but not too much.


Explosive ship decompression from bullets isn't really a thing to worry about as it is more mythological than actual. So really that brings you to how "real" you want your physics to be?

The existence of body armor on a spaceship in a world where this was even semi-common would preclude pressure as a problem for most cases. Crew armor would include by design a pressure suit. Passengers would likely travel in emergency pressure suits - which don't have to be big and bulky for short term use - or have them handy. So the crew on a ship about to get boarded could conceivably suit up and intentionally depressurize before the actual boarding.

They wouldn't have to fully depressurize either. A 50% level (compared to Earth standard) would require suiting up with a minimal pressure suit and air supply, and would greatly extend the time to fully decompress.

There would also be tactical reasons to decompress a ship prior to getting boarded. If the defenders know the ship well and can jam radio communications they force the invaders into a sensory tactical disadvantage. Fighting without auditory feedback on your environment is really difficult without specific and intense training, let alone squad communication.

A good review of the math behind it can be found at this page on spacecraft decompression, but the "one-one-ten-hundred" rule of thumb can help in estimating it. That rule is as follows: "A one square-centimeter hole in a one cubic-meter volume will cause the pressure to drop by a factor of ten in roughly a hundred seconds."

As far as reducing the risk of bullets w/o body armor, look no further than "Dune". There you have the fictional "Holtzman Shield" - a field of energy that slows down or only allows slow moving objects through. If you take a step back from the personal-sized ones in Dune, the idea could be used on a multi-hulled spaceship to minimize the risk of gunfire.

Your world may not have compact enough power sources to power such a device as body armor, but a ship could, thus removing it from being effective body armor. Though of note, I seem to recall in the original Dune movie during the invasion a bullet penetrating the shield and killing the wearer. You could also play off the idea of slowing the projectiles down enough that they can't penetrate the ship hull, but not powerful enough to slow them down far enough to avoid penetrating flesh.

On a personal side, I would drop the expectation that anything but a very high amount of small projectiles or a small amount of large ones would produce catastrophic events during the boarding battles. Unless mass is a non-factor in your world, even boarding troops would not necessarily be firing willy-nilly because that represents mass that had to be carried and thus ammo itself may be at a premium. Perhaps it used to be that melee was the normal way because of the mass of guns and ammo versus, say, a cutlass or brass knuckles. But now with more advances in propulsion tech mass is less of an issue and guns are making their appearance and are being "disruptive".

But either way, those are at least some ideas on how to solve the problem. If you want to be more "hard sci-fi" then that solves your problem for you because bullets are not the threat Hollywood likes to make them into and projectile ammunition is a mass penalty anyway. Otherwise, the "softer the sci-fi" the more flexibility you have to play with things like energy dampening fields that can't be powered by "man-portable" power supplies. I also think you could get more mileage by dedicating thought to how ship design might evolve considering boarding actions and playing with those.


Combat. In. Space.

(Impressive echos trail off)

Using outer space as an environment for combat scenes has unique challenges as it is a unique setting that (so far) very few humans have experienced. The common challenges are: Lighting conditions, Temperature conditions, Pressure conditions, Radiation conditions, Mass Proximity and Collisions.

Lighting Conditions Outer space is typically either very dark, or very bright. As no human has been much further than our own moon, we really don't know how bright or dark true interstellar space is, however, close to our primary, it is quite bright, given that our star is a relatively young one. Visual protection against direct radiant exposure to the sun is important.

Temperature Conditions It's cold out there. Unless one is directly exposed to the sun's radiant energy, in which case it can be lethally hot. A temperature controlled environment is critical.

Pressure Conditions Specifically, the lack of pressure. Most of space is a near vacuum. Humans are used to "one atmosphere" of pretty constant pressure. Protection against the lack of pressure is a must.

Radiation Conditions The sun puts out a lot more than light. Any time one is near a sun (or some planets) one must take into consideration the other types of energy the star is putting out, and protect oneself from it.

Mass Proximity and Collisions Space may be big, but it's not empty. And there is no speed limit below light, either. Bits of dust or pebbles moving along at even a fraction of light speed can punch holes into, through, or effectively explode just about anything. Armor is a big plus.

Sufficient mass will produce gravity gradients of strengths dependent upon the amount of mass in close proximity. Large enough masses will produce a "gravity well" which can be handy for orbiting, but not so handy for plummeting. However, when one is not near a mass, zero-g conditions provide unique challenges and effects which challenge a lot of assumptions.

Spaceship, Starship, and Station Systems

The hulls, viewports, and airlocks all take into consideration the above required protections and conditions. The internal structure will also likely be compartmentalized such that even if one section receives damage, other sections can function independently.

Internal systems should also be designed to handle acceleration stresses, accidental impacts, decompression, and spills.

In fact, one of the greatest challenges to environment-containing objects in space is liquids and fire in zero-g conditions. Liquids scatter and spread based on momentum and surface tension. Without gravity to provide a unifying direction, liquids can scatter quickly and unpredictably, spread into nooks and crannies that would be impossible in a gravity well, and is very difficult to clean up.

Fires expand globally from the ignition source, and follows the oxygen and/or hydrogen, leaving behind pockets or streams of 'dead' air where no one can breath. While this can also put out fires, it is potentially very dangerous. Even a human can knock themselves out with CO2 poisoning simply by breathing long enough in an area with little to no air current and not moving around.

Fire suppression systems such as we have on Earth cannot work in space, as they usually depend on releasing water, foam, or dust into the atmosphere; all three of which depend on gravity to function as expected, and would create more hazards and cleanup than they would solve. Without gravity, fire suppression materials would drift, clump, and clog everything nearby, and eventually get into other compartments, not to mention posing a real breathing risk to any humans on board.


Due to all the above factors, standard gravity-well weapons would tend to cause undesirable problems for any potential hostiles in a zero-g environment. Most weapons of today rely upon blunt force trauma, explosive force, chemical reactions, and cutting or piercing.

Melee Melee weapons (up close and personal) typically rely upon cutting, piercing, or blunt force trauma in order to inflict potentially painful and crippling wounds upon opponents. However, such wounds cause bleeding, as well as potential for messy bits flying around the compartment. If recovery of the vessel or station being boarded is not a priority, then this is still a viable option... except for one thing.

In a zero-g environment, there is no gravity and little to no friction to brace against during the swing. Martial arts likewise suffer from the lack of gravity. Once one has swung or punched, one will continue in the direction of the swing or punch, unless one actually connects and hits the target. Once you've hit the target, however, you will now find yourself moving away from the point of impact.

One possible solution is to artificially provide gripping and bracing points with handles, narrow corridors, as well as magnetic and velcro grip surfaces.

Another downside to melee combat is the potential for breathing in flying messing bits, and the shorting out or damage to equipment and controls.


Projectiles have additional issues in zero-g areas. Chemical projectiles spray residue (dust, oil, bits and shards of metal or plastic, etc.,) all over the place with all the risks that entails. Projectiles are typically moving at higher velocities than thrown or accidentally bumped objects, and can ricochet with disastrous effects.

Explosive and Chemical

Explosions will create over-pressure ripples in the atmosphere, which can be damaging all by itself, not to mention what it does to solid surfaces. If flechette materials are included this sort of attack could be devastating in outer space. Unless one is going for a quick and messy entry, these sorts of weapons are not usually good options in melee combat.

Chemical weapons may be potentially effective - introducing something to the air or water supply can certainly get rid of opposition, however it will not usually yield exciting battle sequences, unless protection is had on both sides.

Viable Options

After all of these negatives, there would seem to be very little one could use, especially if preserving the ship and/or station functions is desired. However, there are a few:

Puffer weapons These are weapons which release a small contained puff of highly inflictive gas, which in concentration will be effective, but will thin out and become ineffective in fairly short order, so as to avoid the wielder also being affected. Mostly used by suited attackers against unsuited victims. An injection variant for use against space suited individuals, with optional cauterizing and poison mods is also popular.

Zapper weapons Zappers are designed to either overload powered suits, or to pierce both softer suits and the person within, and producing enough electricity to incapacitate the victim and cauterize the would instantly, preventing (hopefully) pesky droplets of blood from getting out into the atmosphere.

Sonic weapons Weapons which assault the auditory senses, these weapons can be effective even when transmitted through metal surfaces. It can impede thinking, and shake morale, as well as become extremely painful "Ride of the Valkyries" cranked up to 31 is a traditional, yet still popular, choice. For maximum effectiveness against suited individuals, direct contact is required.

Incapacitation weapons These weapons are designed to pin opponents in place. A simple extendable brace can be used to pin someone face first into a flat surface, though this is typically hard to do in the middle of combat, especially if someone gets tossed and knocks your brace loose.

Magnetizing an opponent can also pin them into place, so long as they can't reach the device's controls.

Restraints are also a popular choice, though this usually requires a victim who has been rendered unconscious or helpless already. Skilled grapplers might be able to snag a limb mid-combat and cuff it to a nearby handle or grip, one by one.

Chemical restraints of a quick-set, high viscosity, and high surface tension nature are less common, but still effective in a quick and dirty way. Emphasis on the dirty. Clean up is a horror, but if your goal is to simply pin them down fast and move on, there is a place for these in your zero-g arsenal.


Combat in space requires some clever thought, a sneaky temperament, and a billard master's grasp of angles, vectors, and velocities; applied to 3D. With some planning and cunning technologists, your narrative space pirates will be terrorizing the space lanes in no time at all.


The only way to win the arms (armor?) race is not to play. Don't try to armor your ships against standard bullets. This does things to the armor market that work in your favor.

The first thing to understand is that most people won't want to wear armor anyway, and most armor-users will want to wear thin, flexible armor that can be easily concealed. Against the first group, "safety rounds" that can't pierce a ship's hull will be as effective as ever. But even against people wearing concealable armor, safety rounds will still hurt like hell even though they may not be lethal, and thus are effective as stunning weapons. The few moments a lightly-armored opponent spends stunned from the pain is enough time for an assailant to pull out some other tool.

Of course, heavier, rigid armor that could truly stop a safety round can be made, but it will be conspicuous. Especially since bullets that can pierce such armor can also pierce a ship's hull, so the market will demand that such armor also be able to function as a pressure suit. So when a ship's surveillance cameras or crew notice someone clanking around, the people defending the ship know that they may need to pull their "elephant guns" (i.e. what we'd call "standard" rounds). Despite the name, an elephant gun might not be a distinct gun, but just a clip of hull-piercing ammunition that fits in the character's usual firearm.

As a result, gunfighters in a universe like this carry one or two guns, and a couple of tools:

  • "The usual gun", loaded with safety rounds
  • An "elephant gun" loaded with standard rounds (or a clip of standard rounds for the usual gun)
  • A "stake": a stiletto made from some suitably strong material to punch through light armor or joints in heavy armor (for those times when the elephant gun just isn't an option). Maybe paired with a hammer for dealing with really tough armor. This is more of a tool for finishing off downed opponents than a weapon per se, though stake-fighting could develop into a kind of martial art in its own right.
  • "Cuffs": Some kind of restraining device. Could be literal handcuffs, or maybe some sort of force field or tranquilizer. For those times when you need to make sure someone isn't getting up again, but killing them isn't an option.

This should, in theory, give you the kind of environment you're looking for. Lethal gunfights, with the added brutality of staking downed opponents at times. Reasonable safety on a shipwide scale, most of the time, but with the possibility for things to "get dangerous" when the elephant guns come out.


As far as I remember it was in the book "Solar Station" from Andreas Eschbach where the walls of the station were filled with a kind of foam which, when the wall was penetrated by a buttet or micro asteroid, closed the leak within seconds. Of course this only works if the holes your weapons punch into the walls won't be too big.

  • 1
    $\begingroup$ I believe that they used a similar idea on Blake's Seven. When a breach was detected the space between the hull and the inner walls was filled with foam. This could handle even fairly large holes, I think at least a square foot, as long as there are extra air to replace the loss. People close to the hole could still get killed, but most would survive. $\endgroup$ – BentNielsen Oct 14 '16 at 8:40

While the Earth's early, short term ships didn't have much radiation or micrometeorite protection, any long term ship has to protect its crew from hard radiation and micrometeorites.

Current micrometeorite protection stops a 7.5mm aluminium projectile at 7km/s. That's of the order of a hundred times more energy than a bullet, though obviously if fired from the inside a bullet hits the pressure hull first rather than the shielding.

Penetration depth of bullets is less than the penetration depth of hard radiation in most materials, including water which is the most likely near-future shielding.

So a realistic ship might have a thin inner hull, a couple of meters of 'water' or ice for rad shield and crew use, then a micrometeorite shield. A bullet will penetrate the inner hull, but stop in the water after 30cm or so. Even without the water it would be stopped by the shielding. The water won't be very pressurised, so expect a bang and maybe a little splashing. Pseudo-gravity from centrifugal effects would mean the water would stay put; microgravity would mean the water might bubble out a bit where the bullet displaced it.

If bullets can penetrate the hull of your spaceship then all your crew are already dead on a long term mission.

By 'water' the load may get replaced with waste products as used, so the splash may be somewhat unpleasant.

  • $\begingroup$ I calculate that to be a little over 4 times, not 100. Kinetic energy = 0.5*m*v^2 so for aluminium (density 2g/cm^3) is 0.5*0.001*7000^2 = 36kJ whereas a bullet 0.5*0.01*1300^2 = 8kJ. $\endgroup$ – Innovine Oct 11 '16 at 19:58
  • $\begingroup$ @Innovine I was thinking around 600J for a typical handgun round such as en.wikipedia.org/wiki/9%C3%9719mm_Parabellum $\endgroup$ – Pete Kirkham Oct 12 '16 at 7:46
  • $\begingroup$ Water and bullet - search "supercavitating bullets", something like that en.wikipedia.org/wiki/Underwater_firearm , 7.62×51mm NATO (accurate range of 25 meters underwater) $\endgroup$ – MolbOrg Oct 12 '16 at 19:19
  • $\begingroup$ @MolbOrg the question was what needs to be changed so that anti-personnel firearms can't accidentally penetrate the hull of a spaceship, not what could be changed so that they will screw with the plumbing. $\endgroup$ – Pete Kirkham Oct 13 '16 at 9:12

I think you can incorporate a style of energy weapon. I agree that lasers don't sound promising, but more of a plasma/electric type of ammunition could be an appropriate tool if one is open to such an approach.

In this scenario the hull has a lot of mass, and can disperse large amounts of energy blasting into it without issue. Just taking the same material and creating an armor plate wouldn't work, as the energy needs to dissipate somewhere. If shot in the chest it would just ark from the plate through their legs and into the floor.

They could get a full-body suite beefy enough to route some of it to the hull -- if the floor is even the right material. But the conductivity wouldn't be ideal so damage wouldn't be eliminated, and the encumbrance penalties would be significant. That is, they'd have textbook heavy armor.

  • $\begingroup$ Welcome to Worldbuilding.SE, Thomas! While you have a well-reasoned argument, here, this does not quite answer the question @openend asked. In his/her first bullet point, they explicitly said "no energy weapons please." Now, at the end, they do invite you to "get rid of one or more of these requirements," but the implicit requirement there (in your case) is to then also include a compelling argument for why kinetic weapons cannot work in the scenario by openend. I'm not sure that "energy weapons are better" will fly, so maybe you can think of a more interesting reason? Again, welcome. $\endgroup$ – type_outcast Oct 11 '16 at 17:11
  • $\begingroup$ Fair enough. The question he posted in that bullet point led me to think the matter was still open ended. No pun(s) intended. $\endgroup$ – Thomas Oct 11 '16 at 18:33
  • $\begingroup$ Aw, it was a good pun. :-) Remember, you can always edit your own answers to incorporate feedback or improve them in general. Later on you'll even be able to edit others' posts in the same fashion. So feel free to improve your answer if you can! $\endgroup$ – type_outcast Oct 11 '16 at 18:44

I'm thinking... for what purpose would you board an enemy spaceship? I can only think of 3 options...

  1. To capture people on board.
  2. To capture the spaceship
  3. Data gathering from the spaceship itself

As far as I can see, all three options rely on the spaceship being pretty much intact. Option 1, you can't harm the spaceship in case it depressurizes and the people die. Option 2, no point in harming the spaceship heavily, although you may disable it's power to make it easier to take over. Option 3, the more you damage the spaceship, the more likely you are to destroy data on it.

Therefore if I was going to board a spaceship, in the best case I'd disable it's power, so it can't move and can't fight back, then if possible I'd pump sleeping gas into it, depending how big it is, and then enter the ship with gas masks on.

If that's possible, it's easy, but otherwise there's a range of weapons I could use on the enemy, and depending on circumstances, some wouldn't even require an entry to the ship: ie, the attacking spaceship could use them from outside the ship. I could use:

  1. Taser Shockwave - idea of electrocuting lots of targets with a single wave
  2. Radar targeted laser guns - whatever armour the enemy has, they will still be able to see. Use a short range radar to target their eyes with a laser and temporarily blind them.
  3. Active Denial System - radar waves that causes intense pain
  4. Vomit Gun - use of pulsing lights to make the victim vomit
  5. Water jet - powerful enough to knock a human over or stun them, this wouldn't penetrate metal.
  6. Flame thrower - no practical armour is really proof against high levels of concentrated, sustained heat.

Most of these should work with armour, if the victims are unarmoured, the job becomes a lot easier, I can use tasers, electric swords, close combat stuff. Maybe the use of droids etc can target the ship's systems itself as well.

Note that all these things can be used by those being attacked, in defense. In addition, it probably makes no odds to the victims if they can blow apart the attacking spaceship.

just my 2cents, it's an interesting question!


(You don't say what kind of physics might be acceptable, but it appears that things like energy weapons are plausible somewhere in your universe, suggesting exotic physics)

"But just build a body armor out of it, and you’re bulletproof" and similar arguments in answers can perhaps be worked around.

The ship is much much larger than a crew member / combatant; if the hull shielding incorporates some sort of active dispersal (whatever kind of "field" physics makes sense in your world) which spreads the kinetic energy of a small impact across the entire area/volume/mass of the hull material (and possibly an additional mass sink somewhere in the ship) it would take an inordinate amount of energy to even scratch the hull - but a combatant suit with comparable technology could only spread the impact over its own area, very much tipping the balance. Whipple shield 2.0, needs a catchier name.

(The same technology is likely to be rather useful for attacks from outside the ship, too, although ship-to-ship combat and breaching forces may use much larger kinetic energies, and perhaps energy weapons there aren't excluded from your scenario.)


One more or less realistic solution is to use a laser gun.

Soviet laser gun

Allegedly, a prototype of a laser gun was developed in scope of the Soviet space program for military purposes (the Polyus space station).

  • $\begingroup$ This is specifically disallowed by the OP. «For example, lasers can easily be nullified by reflective armor. Is that right? In this case, no energy weapons please.» $\endgroup$ – JDługosz Oct 11 '16 at 13:20
  • 2
    $\begingroup$ @JDługosz: Not everything reflects all radio frequencies. And a material that is reflective at some frequencies are transparent to others. So you can in theory have a star-trek style configurable frequency weapons. $\endgroup$ – slebetman Oct 11 '16 at 13:42
  • 1
    $\begingroup$ @JDługosz The OP said no laser weapons based on the premise that reflective armor would nullify them, which I don't think is the case. Variable frequencies and pulsing the beam both would significantly reduce the efficacy of reflective armor. Plus, much like modern body armor, you can't protect everything. $\endgroup$ – Jason K Oct 11 '16 at 13:45

I think the easiest is a highly advanced non-Newtonian fluid armour in the ship. From this video, a giant gummy bear stops a bullet and a gummy bear is a kind of non-Newtonian fluid.
This armour running behind the inner panels and outer armour ought to prevent kinetic slugs punching through the hull.
This layer could be quite thin, and potentially serve other functions (conduct electricity around the ship). It would also add to the carnage as it now becomes ship 'blood'.


Since internal ballistics of any kind (from, say, an explosion internally) are bad, why not have whipple shielding on both the inside and outside of the outer hull?

This is essentially spaceship Kevlar (very dumbed down description, read the wiki article). It is put on the exterior of spaceships to help reduce and prevent damage from debris and micrometeorites by absorbing and redirecting the kinetic energy from the impact before it reaches the primary hull (often shredding debris and making it effectively harmless). Make the outer hull also have this design on the inside (perhaps only in exposed corridors where explosions or boarding actions might take place to save weight/space).

Effective whipple shields against bullets would be too heavy/bulky to wear individually (though, there is probably something better at keeping a person alive against small arms fire than a whipple shield in your universe).

That said, why would a boarder care about putting holes in an enemy ship? Presumably they would be in some kind of armor/suit to protect them from the environment. There's no guarantee that the enemy vessel will have an intact hull (as most boarding actions happen after/during a battle). If anything, depressurizing the entire ship would help the boarders take control of it, and any holes can be fixed after the battle.


In Seveneves ( which is a super enjoyable book and well worth reading ) the necessity of not making holes in spacecraft results in the development of catapult based weapons. These don't fire far, but they don't need to in the constrained area of spacial habitats. What makes them interesting is that instead of regular projectiles, they fire small anti-personnel robots, that may attack the moment they land on a target, or crawl around the target looking for a chink in their armour. Consequently arms races develop in defensive and offensive robotics as much as in the weapons to launch them.

  • $\begingroup$ Ive already read that one. And although they are interesting, I just dont want them neuropincher robots in my project :) $\endgroup$ – openend Oct 11 '16 at 21:10

It depends on what your assailants goal is. If they want to capture the ship in working order and those on the ship presumably want to repel the attack while maintaining the ship they both have the same limiter on weapons.

If the assailants want to destroy the ship and are close enough to board they may just use explosives rather than precision firearms.

I think the major reason fiction often talks about firearms in space ships as a catastrophic situation is as a device.

It's often more interesting when you are forced not to use firearms, or it's an easy way to build threat when a gun does more than just shoot someone.

Many people who already posted have good solutions for ultimately using firearms anyway. Depending on the story you are writing do what is most interesting and come up with a justification that fits your world.

Could also go the Dune route and say firearms left favor and have their resurgence be a tactical coo for one force.


Super bouncy balls...fired from an automatic air canon at incredibly high speed. They will hurt and continue as a distraction long after they are fired. If you use the ones that have a strobing LED inside it will be psychedelic! OK, not very realistic but illustrates a point.

Seriously though...

Basically anything big and slow transferring a lot of energy will do the trick. It won't be very effective on anything hard, like the hull of a ship, but launch something hard enough and the human body just isn't strong enough to prevent dislocated joints and broken bones.

Another possible non-penetrating option would be something like from the animated movie The Incredibles. Sticky balls that expand are fired at the target(s). If they are very difficult to get off they become a distraction and then a disabler. If you want to be truly diabolical, mix in a skin irritant that becomes a true distraction!

  • $\begingroup$ Seems like that's nearly as dangerous to the attackers as those being attacked. $\endgroup$ – Innovine Oct 12 '16 at 9:24
  • $\begingroup$ True...just trying to illustrate a point about possible non-lethal distractions. I've edited as such. $\endgroup$ – Steve Mangiameli Oct 12 '16 at 14:11

protected by Serban Tanasa Oct 13 '16 at 13:36

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