In a science-based universe with a species physically similar to merfolk, so tails and arms, what weapons would they develop for use during the stone-age phase of their existence? These would be used both for hunting and for skirmishing with other tribes although fights involving more than 30 or 40 people would be highly unusual.

The underwater environment provides a number of constraints in the ways weapons can be used and designed, but does it also allow other new options?

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    $\begingroup$ Possible duplicate: Weapons for Mer-people $\endgroup$ – DaaaahWhoosh Nov 27 '15 at 17:37
  • $\begingroup$ Tim, an author named John Ringo has a book series named The Council Wars. In one of the novels merpeople have to fight against and defend themselves from other mutated-human species (they take the form of other sea creatures). Might be worth your time to read a few of the fight scenes. They basically use pike spheres (instead of walls) as a fight formation, etc. The novel's name, I believe, is Emerald Sea $\endgroup$ – AndreiROM Nov 27 '15 at 23:55

10 Answers 10


Shivs, that is improvised sharp small weapons.

You cannot throw or shoot anything underwater. Friction stops it very quickly.

Take a sharp rock, or a shell of some sort. If it is sharp all over wrap it in something to be able to hold it. And there you have it.

As technology progresses you probably want longer weapons to outreach the opponent.

You can not slash underwater without expending a lot of energy, stabbing is much easier. This means spears, which is basically a shiv on a stick.

However, you don't want very long spears, since they become harder to turn to face a moving opponent. A two-ended spear is a possibility, but I don't know how practical it is.

You can possibly get a rock/paper/scissors situation where short spears beats shivs, and long spears beats short spears, but shivs outflanks and beats long spears.

One major difference is that battles are 3-dimensional. This makes battle tactics much more complicated. The short version is that it is easier to out-flank, but harder to fully surround someone. I don't know much more than that about this, but I expect being able to outsmart the opponent will be more important than in land battles.

So far, the water has been a problem, but as you say it can also be an advantage.

Take a really big rock. Fasten a lot of gas bladders to it to make it float. Push it to directly above an enemy village or other target. Cut away the gas bladders. Smile.

  • $\begingroup$ Make spear. Put spear in kelp sling. ???. Profit. $\endgroup$ – Joe Bloggs Nov 27 '15 at 16:17
  • $\begingroup$ As for surrounding, an outfought enemy may be pressed against the surface or against the seabed. (Depending on whether they breathe water or air). $\endgroup$ – Dallaylaen Nov 28 '15 at 12:12
  • $\begingroup$ Very few of the other answers seem to have accounted for just how big a problem friction is underwater. I'm fairly sure ranged weapons would be it of the question, unless you had a strong enough elastic material to create something like a speargun, and even then they are very short ranged. $\endgroup$ – Toadfish Feb 15 '16 at 3:01

If they were to somehow use kelp or say bamboo that was growing near the edge of water they could fairly easily create telescoping spears with say a gas bladder being popped as the propellant. This could be used in place of say a bow and arrow with reduced range.

But Stig Hemmer brings up a good point about slashing and 3D battles, which to me says that they would develop a way of using their clothing as a weapon say for example a helmet with the snout of a swordfish on it that is large enough to skewer other merfolk. At that point combat would depend a lot more on agility and swimming capability.

Some other thoughts that i had:

  1. kelp nets = to reduce the movement of enemy troops.
  2. domesticated predators = to act as hunting dogs of sorts.
  3. concentrated poisons of say a puffer fish = suicide bomber style attack to take out multiple targets.
  4. gas bladders = stick one of these into an opponents gills and pop it to cause the same affect as sticking a humans head into water for 10 seconds, not to mention the damage of forcing something into gills.
  5. a tail fin = made of coral or shells that allowed for faster swimming speeds and it has a sharpened edge the in close quarters combat could be swung at an enemy to cut them open.

That's All I got hope it helped!

  • $\begingroup$ How would covering the tail fin in coral or shells increase the swimming speed? $\endgroup$ – Burgi Dec 2 '15 at 13:57
  • $\begingroup$ I didn't explain that one very well.. what i meant was creating an extender or prosthesis that made the tail fin longer. it would increase the surface area of the tail and the amount of water they could move thus allow them to swim faster. @Burgi $\endgroup$ – Akmedrah Dec 2 '15 at 15:41
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    $\begingroup$ OK that makes more sense. Like flippers on a flipper... $\endgroup$ – Burgi Dec 2 '15 at 16:06

I think another effective tactic for underwater combat would be to obscure sight, much in the way cephalopods do (https://en.wikipedia.org/wiki/Cephalopod_ink) in order to escape danger. However, for this application, I imagine using an ink sac for creating a cover of darkness for highly-trained underwater combatants to come in close with a sharp object and do the deed quickly and accurately.

  • $\begingroup$ That's a really neat idea. :) $\endgroup$ – Tim B Feb 15 '16 at 19:46

Since mobility underwater is a major factor, I would be designing weapons towards the aim of hindering or trapping opponents so that the short range stabbing weapons mentioned in other answers can make short work of them. Think of barbed nets, harpoons to impale and tangle, even just wrapping ropes around limbs, etc cetera. Consider weighting them to drag them deeper, or even the opposite, if you could somehow deploy an inflatable bladder that would drag them to the surface.

Visibility is also often limited in aquatic environments — create confusion with clouds of ink, like a cephalopod; or shimmering clouds, like a shoal of small fish. Actual cephalopod ink sacs would be a good resource to use for this, or something like mother of pearl or shiny metal pieces for the latter. To prevent an enemy from escaping in dark or murky water, you could even maybe attach noisy objects to them.

Lastly, and this is a little more fantastic, if your environment had bioelectric organisms handy, you could maybe try to harness this effect — as long as you could come up with a way of preventing it from hurting you as much as your opponent. Electric Ray on a stick?


I'd suggest that in such a situation one of the things you might see is an increased reliance on domesticated sea creatures for war - after all, it is generally preferable to fight over long distance if at all possible as it places you in less direct harm's way. Think leopard seals, sharks, giant squid etc. You might even see such creatures bred specifically for war, with bigger teeth and leaving nastier wounds.

Weapons, unfortunately, would likely be limited to spears, swords, knives and axes due to the extra drag imparted by water.

This leads to interesting tactics. An army which relies on creatures has more mouths to feed and is thus more reliant on good logistics. The three dimensional nature of warfare in the ocean also means that you might have vastly different creatures in very different roles. Indeed, over a large enough scale, you may start to need to take into account pressure in both animals and protective equipment for your mer-people - a creature that can fight effectively at -400 ft would struggle at -4000.

  • $\begingroup$ Hmm, in general I don't think pressure is a big deal for most underwater species as they are in equilibrium with their environment. They don't try to keep the pressure out. $\endgroup$ – Tim B Feb 15 '16 at 10:18
  • $\begingroup$ In general no, but if you were to try and use a war-seal at 4000 ft, I don't think the pressure would be very kind to them. Same with Colossal Squid - I can't find a source right now but I seem to remember that the eye of one caught was damaged due to the pressure difference of deep sea VS open air $\endgroup$ – Miller86 Feb 15 '16 at 10:24
  • $\begingroup$ Yes, seals being air-breathers will find it harder the deeper you go. $\endgroup$ – Tim B Feb 15 '16 at 10:26

I'm answering this question taking into account how you could use the environment with a stone age equivalent knowledge to help you in your attack/defence with a little bit of fishing thrown in. these are the sorts of things that you could learn from trial and error and don't need any futuristic tech or knowledge base to decipher.

As on land, Use nature to guide you in your underwater tactics. It's pretty much already solved most of the tactics aside from weaponry.


  • Breathing and air supply are not an issue. But hey, even whales need to breach every now and then, so if necessary take that into account.

  • You have some sort of thermal insulation from the cold.

I’ve listed several things to take into account

1) Light & Darkness = One very important factor to take into account. Little to no light reaches beyond about 100-200m of the ocean surface So you could either use the darkness to make surprise attacks or retreats from below or you could force your opponent into the darkness to disorient. For this you would need some sort of light source or visual enhancer for yourself.

2) Bioluminescence = Nature has several bioluminescent species which create their own light. You could bottle up a couple bright sources. Either use them as 'torches' or if they are particularly bright (it's a make-believe world, so you can make them as bright as you want) you could cover them up, take them into a battle in the dark depths and then suddenly unleash a light bomb on your unsuspecting enemies. Making either an attack or retreat under the cover of ...lightness!

3) Water pressure = The deeper you go, the more the pressure. So long wavy spears won't work in the deeper depths and close combat swimming would be the order of the day. Whereas it could be the opposite in the shallow depths where it is easier to wave a long stick through the water.

4) Speed = I'm not sure how water pressure would affect projectiles. Maybe make shooting them upwards easier and could be considered the equivalent of the high ground. I know from experience that swimming underwater is easier a few metres beneath the surface where the pressure is more uniform around you. Swimming would be faster deeper down, but large quick movements slower. Stabbing would be easier than slashing, think more Zulu assegai than dancing twirling spears and halberds (axes on sticks).

5) The Bends = Water pressure could be used to your advantage by forcing your enemies to rise too quickly and get the bends; Nasty way to go. Or at least too much pressure on the ears. Think in terms of mammoth hunters tagging each other out when they got tired of running (ie you need to stop and decompress yourself). This would involve preplanning and groups of people waiting at designated depths.

6) Extreme temp variations = Some ocean valleys have hydrothermal vents, with super hot water; Force your enemies to either burn or flee. The same in the polar regions. There is a rare event where seawater freezes and the remaining denser saltier water forms a downward 'tendril' or brinicle reaching for the seabed freezing everything it makes contact with. It was called an Icy Finger of Death. I must say it is one fantastically magical looking naturally occurring event.While we would be fast enough to avoid getting stuck in it (it takes about 12 hours in real time to form), it could catch a few arms, legs, tails unawares, if you were distracted or trap a wounded unconscious soul. If you are just hunting for food, it could be a cool drive by - pun intended. Just chip out want you want and move on.

7) Currents = Use the currents to your advantage. If you fighting in the depths you could force your enemies into an upwelling current, and again they die of the bends if they can't get out quick enough. Or you can use a downwelling current to quickly escape/retreat. Get yourself away from your enemy, and then take your time to rise back up to the surface when you feel safe! You could string up some huge nets (material of your choice) downstream and then fight and drift downstream guiding your enemies into the nets.

8) Sight= Warmer, slower currents are normally sediment laden, so visibility will be poor. Colder upwelling water is filled with nutrients and is therefore teeming with life. That's why the fisheries are always located in those regions. So you can use the wildlife to your advantage to distract/ hide in/ lure in some predators or just easy fishing etc.

9) Sealife patterns = Ocean wildlife also has an oscillating pattern according to the day night system. Depending on the species they will rise to the surface and sink to the depths during the night and day to take advantage of light and nutrients. Some of this is passive like, phytoplankton. Teeny tiny bits of grub feeding off other teeny tiny bits of grub. Others use their own propulsion to take advantage of the rich easy food pickings. Think jellies. Masses of stinging jellies. You could time your attacks to coincide or avoid, whichever floats your boat.

10) Also think BLOOD = Are there any sharks around. They are apparently the bloodhounds of the sea - I wouldn't want to stick around a battle/hunting location too long. You would need some sort of substance to cover any wounds and wrap kills in that will prevent the sharks following you home. Unless you like having lots of sharks right outside your front door or that is your intention to lure them somewhere. I'm thinking some sort of waterproof gel-like slime or fish mucus etc - something that sticks and seals at the same time and/or some sort of sealed container for any bloody kills.

All of these features would and could be used to their advantage by a people living in the stone age. It's just up to trial and error for your swimmers to figure it out. The world is your oyster!

I would highly recommend watching the BBC's Blue Planet and Frozen Planet for how ideas on how the natural world works and use that to inspire tactics that would work in those situations.

  • $\begingroup$ Nice ideas, although the bends would only apply to surface air breathers without suitable adaptations. $\endgroup$ – Tim B Jun 19 '16 at 21:07
  • $\begingroup$ True. I was thinking more along the lines of people being forced to move and live in the sea on that one (with some adaptations of course). $\endgroup$ – EveryBitHelps Jun 19 '16 at 21:22

There probably wouldn't be a lot of difference between stone age weaponry whether it's developed for use on land or under water. Short spears would dominate melee combat. Projectile weapons would have reduced range under water, but would still provide some advantage over melee weapons. Atlatls are spears launched by a hand lever, which is a very simple concept that many groups of early Humans discovered independently. Bows and arrows are a logical evolution of the concept of a propelled spear and would also be practical with stone age technology. Retrieval and reuse of projectiles may be difficult if they sink, so a thin line made from kelp or a similar material might be attached to retrieve the projectiles once fired. This would also be very useful for hunting small animals as they can be reeled in once impaled on the projectile.

Domesticated animals may be used as weapons in underwater warfare too. For instance, whale like animals may be used to lift nets filled with rocks that could be lifted over a group of enemies and released as a sort of primitive artillery bombardment.


If they ever develop chemistry and metallurgy as we know it, they could build ranged weapons like spear guns, torpedoes, and even guns that fire supercavitating rockets instead of bullets. They would need some semblance of industry in order to develop such weapons, but seafloor mining and chemicals that burn underwater exist in our world, so it's not impossible.

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    $\begingroup$ While this is true I specifically was looking for low tech weapons so I can't upvote. Thanks for the suggestion though. $\endgroup$ – Tim B Feb 14 '16 at 22:58
  • $\begingroup$ Ah, I seemed to have missed the part about it being a stone age civilization. In that case, spears are really the only option, but maybe some adaptation of the atlatl (a thin spear launched by a lever) would be useful as a ranged weapon. Perhaps even an adaptation of the bow and arrow concept could work too. Swimming above an enemy and dropping something heavy on them like a large rock could also work. I can see domesticated sea creatures also being used as weapons. $\endgroup$ – Elijah Decker Feb 14 '16 at 23:09

If they somehow have access to terrestrial bamboo or something like it they could make air filled spears that when released at depth will shoot up to the surface.


I agree with the answers already given, short stabbing weapons would likely dominate combat. I would add that bone would likely be a common building material for these weapons and other tools. They were used commonly by humans and Neanderthals at a low technology level. This would seem even more likey underwater where wood is uncommon.



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