My setting contains modified humans who live on an ocean planet with only small pockets of land. Generally, large populations of people live on these small islands but since land is so restricted, they get most of their resources from the sea in the form of fishing, diving (foraging/hunting), or underwater farming. Luckliy, the humans are able to hold their breath for a long time (over 30 minutes) and can see rather well underwater (due to genetic adaptation).

Unfortunately, the sea is not safe. Diverse threats, large and small, lurk in the deep. Everything from giant kraken to tiny piranhas love to snack on humans. That's why the humans need to defend themselves. Generally, the intelligence of the attacking creatures is primarily bestial/instinctive. Only very few underwater threats are capable of more than animal cunning.

What melee weapons or combat techniques could be used to:

  • Fend off foes while diving (curious sharks and more aggressive monsters)?
  • Defend ships from emerging attackers (think giant kraken tentacles)?

Technology level:

  • Bone, wood, and fibrous materials are available in great quantity along with other materials that can be harvested from the sea such as shells, shark teeth, and coral
  • Metalworking technique is advanced and complex. Alloys can be made and furnaces can reach extreme temperatures but metal itself is very rare. Metal tools, cooking instruments, and weapons are often family heirlooms and highly valued.
  • Glassmaking and ceramics are suprisingly advanced. Large amounts of glass can be produced, even at high clarity
  • Ranged weaponry like harpoon guns exist however aren't really man-portable but rather ship-mounted.

Thoughts I've had:

  • Slashing or crushing weapons such as hammers or swords would be greatly slowed by the water and rendered almost completely useless.
  • Piercing weapons such as harpoons or rapiers might be effective.
  • Arm-guards or bracers which bait the creature into latching on could bring it into knife-melee range
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    $\begingroup$ i gotta say, the proposition of humans who are essentially also penguins sounds very romantic. $\endgroup$ Feb 6, 2020 at 16:18
  • $\begingroup$ How would a ship defend against a sea creature, and possibly win? $\endgroup$
    – Mazura
    Feb 7, 2020 at 3:33
  • $\begingroup$ Depending on how many monsters there are, they could start poisoning them with suicide divers. They could also try to attach weights to the bigger targets to slow them down. I imagine a giant octopus would rather rip its own tentacle off than pulling a boulder over the sea ground. $\endgroup$ Feb 7, 2020 at 9:35

9 Answers 9


Fend off foes while diving (curious sharks and more aggressive monsters)?

You don't. When there are large predators around, leave the water.

This is fairly standard behaviour in hunter-gatherer societies. Big predators are exceedingly dangerous, and when your society lacks things like antibiotics, you absolutely don't mess about with the possibility of being mauled because even if you do fend off or even kill your opponent you'll probably end up dead as a result of infected wounds. Its a big risk for very little reward.

Marine animals are no different. Predators like sharks or seals are strong, fast and clever and they have keener senses than you. Don't mess around; leave the water and keep what you've already hunted and harvested. Don't try and spar with them, because the risks are just too high and there's a pretty good chance that knife, spear or no, you're gonna lose. I absolutely would not be mucking around with shields or vambraces when faced with something that can eat me!

Defend ships from emerging attackers (think giant kraken tentacles)?

For the classical "an octopus just grappled my ship and is staring at me whilst eating my crewmates" axes and spears are perhaps the order of the day. Cephalopods generally aren't very well armoured, and they are often very tasty. Get hacking. Once you've collected a bit of calamari and jabbed it in the bit that might be its face, maybe, it'll probably leave you alone.

The big problem is that those things are probably quite clever. They'll learn. A giant kraken would be better served by grabbing your ship at or below the waterline, and then using its huge and very hard beak to bite chunks out of the hull. A sinking boat won't be putting up nearly as good a fight as an unharmed one, and the four-limbed snacky things will come out of their own accord.

So once again, the answer is "you don't". Go sailing in flotillas and watch out for one of the other ships being sunk. When that happens, run away.

Remember that in a world where surface land is rare, making new boats will be a costly enterprise, and careless deforestation could spell the end of your society. You don't want to risk your own life, and you won't want to risk the most valuable possession you have, which you may have inherited and be expecting to pass down to your children. Don't go sailing where the wildlife will eat you.

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    $\begingroup$ hunter gathers fend off or kill large predators all the time, the trick is they do it in numbers and from a distance, they minimize risk, but leaving large predators to close to your village if far riskier than combat. $\endgroup$
    – John
    Feb 7, 2020 at 1:12
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    $\begingroup$ "That's why the humans need to defend themselves." - no, that's why they need to leave. Holding your breath for 30min and better eyesight doesn't make you a master of the underwater domain. - What is this, Waterworld? Dude had gills and webbed feet. $\endgroup$
    – Mazura
    Feb 7, 2020 at 3:50
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    $\begingroup$ @StarfishPrime except that's the point they don't always go, you can't wait out a predator that has no intention of leaving. Plenty of technologically primitive cultures hunt sharks, even the largest sharks. Hunter gatherers killed off most of the Pleistocene mega fauna, don't underestimate the killing capabilities of primitive humans. $\endgroup$
    – John
    Feb 7, 2020 at 11:10
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    $\begingroup$ "The four-limbed snacky things will come out of their own accord" is just precious! :D $\endgroup$ Feb 7, 2020 at 11:15
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    $\begingroup$ @John Yes, they hunt sharks. Mostly with spears from the relative safety of their boats. Out of interest: Can you tell me which culture does it by diving at them with a melee weapon? $\endgroup$
    – Kakturus
    Feb 7, 2020 at 12:47

The Greeks had it right when they armed Poseidon with a trident.

Because of the resistance of the water, any melee weapon that depends on a "swing" to do its work (swords used for cutting, axes, clubs) will be hampered, but those that depend on a "thrust," that is moving along the length of a linear sort of weapon, will be almost unhindered (this has to do both with the velocity of the movement, and with the orientation of the weapon relative to its striking velocity).

Hence, spears (and spear guns) -- and trident is just a spear with some width to it, decreasing the likelihood that some quick-reflexed enemy will dodge the head when you thrust.

The classic Roman gladiator combination, of a trident plus a net is probably also derived from Greek fishing tools -- though a net can't be effectively thrown underwater as it might be in an arena, it can still be used to entangle an opponent's weapon. Questionable whether it's more useful than a buckler shield, but retarii used both, the shield being small enough to allow use of the net without dropping the shield.

So, there you have it -- your underwater fighters who, for some reason, can't make a crossbow work underwater, should carry a trident, net, and small buckler -- and practice with them, because those aren't an easy combination to use well.

  • $\begingroup$ Trident (or a pitchfork) is a so-so melee weapon because it's easy to block. It's good only for smaller opponent who's only defense is to flee. $\endgroup$
    – Alexander
    Feb 6, 2020 at 19:14
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    $\begingroup$ @Alexander it isn't a whole lot simpler to block than a spear, a design which was popular for quite a few thousand years and killed quite a lot of people. $\endgroup$ Feb 6, 2020 at 19:19
  • $\begingroup$ @Starfish Prime I found this popularity very limited outside of ritualized tournaments. Do you know of any soldiers or knights using tridents (or pitchforks) in real combat? $\endgroup$
    – Alexander
    Feb 6, 2020 at 19:26
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    $\begingroup$ The way I read the question, the weapons are more for slippery-but-dangerous sea creatures than other people. Trident to stab/capture them, net and buckler help keep things like tail stingers out of your face. $\endgroup$
    – Zeiss Ikon
    Feb 6, 2020 at 20:00
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    $\begingroup$ @Alexander having actually done some sparring with pitchforks (which probably aren't as nice to fight with as a trident due to being curved and not barbed) it's only very slightly easier to block one with a shield (The user can twist the tines around the central axis quickly, so you have to block the center regardless unless your opponent is a klutz). This is offset by the fact that it can bind limbs, weapons, and yes, even someone's shield. They're not great against heavy armor. For that you'd want a poleaxe. But for unarmored foes they're a decent choice. $\endgroup$
    – Perkins
    Feb 7, 2020 at 21:48

Fight Fire with Fire

(Fight fish with fish)

Historically, man’s strength in combat against nature has been brains, not brawn, and the same is true here. Domestication is an art that is (mostly) unique to humans. We protected our herds from wolves by making wolves into dogs, and our storehouses from pests by domesticating cats. We have also have domesticated or tamed a number of marine animals, some for warfare. A brief list:

  • Goldfish (domesticated)
  • Koi (domesticated)
  • Siamese Fighting Fish (domesticated)
  • Orcas (trained)
  • Dolphins (trained)
  • Seals (trained)
  • Sea lions (trained)
  • Sharks (allegedly trained but sources are spotty)

These animals live their lives in water and are better suited to it than adapted humans. Use them! A species with good reason to domesticate the larger predators will be able to make more progress than we have, and we’re no slouches at training marine animals (see Sea World, or the US Navy’s use of dolphins and sea lions).

Pods of orcas can take on big threats, and fighting fish or dolphins can tackle pests like piranhas.

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    $\begingroup$ Sea mammals? Awesome! Are goldfish and koi "domesticated"? Just because we keep them in bowls and ponds doesn't mean they want to be there. I would be convinced if you gave them a choice between freedom in a lake vs. food in an aquarium, and they chose the aquarium. I doubt you'd get many takers, tho. $\endgroup$ Feb 7, 2020 at 20:58
  • $\begingroup$ They are on Wikipedia’s list of domesticated animals: en.m.wikipedia.org/wiki/List_of_domesticated_animals $\endgroup$
    – Daniel B
    Feb 7, 2020 at 21:08
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    $\begingroup$ Yeah, I know folks call them "domesticated". I'm just questioning what that really means for fish. Can you go diving with them and they will swim up to you without fear? I think it just means: "Humans keep them as pets", rather than: "They accept cohabitation with humans" in the way that dogs and rabbits and parakeets do. For instance, could you train a school of goldfish to attack prey? Or stay within the limits of a "goldfish farm" without a fence? $\endgroup$ Feb 7, 2020 at 21:25
  • $\begingroup$ I genuinely don’t know: this paper may provide some insights. researchgate.net/profile/Fabrice_Teletchea/publication/… $\endgroup$
    – Daniel B
    Feb 7, 2020 at 21:34
  • $\begingroup$ @LawnmowerMan It depends on what you mean by "domesticated". Domesticated spiders, for instance, don't really behave differently than their wild counterparts. For example, a tarantula in a cage at home may only be marginally less likely to bite than one you find in the wild, provided you are smart about when and how you handle it. On the other hand, a species we would absolutely call domesticated (like a house cat) can still easily become feral and mistrusting of humans under certain circumstances (which don't always necessarily include cases of abuse). $\endgroup$
    – Abion47
    Feb 8, 2020 at 0:20

As everyone else has said, poking weapons versus swung weapons. Tridents, spears, spikes, big hooks, that sort of thing.

I have a question though. A bow may not be a great weapon under water over any great distance, but what about a tube type spear or spike thrower? It depends on how good your people are at making rubber or rubber like material. Or can you arrange a reel and pulley system along a tube that could use mechanical advantage to push something pointy out of the end of the tube with greater force than could be done by hand? This could give you a ranged weapon (not a huge range but maybe enough). That's one thing you could do that would be interesting. Launching things out of a tube like a modern spear gun.

Second, if your people can manage an explosive gunpowder like compound and an impact primer, you could give them shark sticks or the equivalent. poke the adversary with the end of the stick, the primer gets punched and the end of the stick goes bang. What comes out the end is up to you. Modern ones are basically no barrel shotguns. They are effective because the range the projectile travels through is 0 so there is not a lot of energy loss from travelling through water. Using shattered glass as shrapnel could be particularly nasty.

One last thing. Underwater combat is three dimensional, not 2. An enemy can and will come from any direction. You can mitigate somewhat if your people stick to the sea floor as much as possible to reduce the chance of an attack coming from below. They can also take advantage of being able to ambush from below themselves.


Your thoughts are correct.

Melee weapons are a poor choice underwater: the drag caused by water will prevent the user from giving the weapon enough momentum to deliver an effective blow/cut.

Moreover I remember that as a kid I have tried fending something large in the water, like a knife or a blade: as soon as I made the error of tilting a tiny bit the surface with respect to the flow, the thing would go where it pleased itself.

If you think about it, all fishing tools are piercing weapons, not impact weapons, so that thanks to their shape they can have better hydrodynamics and deal damage.

You might want to consider dropping stones and boulders from above the surface, but that has obvious limitations.



Lots of folks have mentioned domesticating marine mammals, and I think that is indeed the best defense against most hazards. If we model Kraken as giant squid, then the natural enemy of these beasts would be: the sperm whale. The trick is to get the whales to protect your boats. It turns out that sperm whales like cephalopods of all sizes, including normal octopus and cuttlefish. Thus, you probably don't need to fully domesticate them, as long as you can tease them with an occasional snack so they follow your boats around. Once a kraken comes to attack, the whales will feed on their own. If kraken love the taste of human flesh as much as humans love the taste of calamari, then they will be naturally attracted to human shipping, and sperm whales may simply learn that human boats are a good place to hang out for kraken-feast. Still, the occasional bucket of squid or cuttlefish can help reinforce this behavior.

Spike Bombs

Ok, so these are not "bombs", as such. Rather, your merfolk can create small spiked balls maybe the size of a basketball, with long, glass/ceramic/bone spikes sticking out of it like a puffer fish/porcupine. The center of the ball is a cage for a tasty treat (small fish, crustaceans, whatever the local predators like the best). They just tow these behind on a short rope when they're diving. When a curious predator swims by to see how tasty they look, if it looks like they can't fend them off with weapons, they just stab the critter in the ball, cut it loose, and let it drop away. Hopefully, the predator will go for the easy snack instead, and with any luck, impale itself with the spikes as it tries to get at the bleeding critter inside. If you manage to kill it with the spike ball, great! If not, a mouthful of spikes should hopefully be enough deterrent to make the predator go nurse its wounds for a while. After all, shark blood in the water will attract orcas just as surely as fish blood attracts sharks.

Also, the spike bombs might work on multiple predators, or even be recoverable! Eventually, predators might learn to ignore them, so the merfolk would need to make them quite varied so as to frustrate natural learning. They should make them different shapes and sizes, and try to make most of the spikes transparent glass, so it's harder to tell what it is.

Scale Armor

Small predators like piranhas won't go for the big spike balls, so body armor is more appropriate. And what better armor than the scales of fish which are naturally immune to small bites? Introducing: the arapaima. Catching enough of these to make a full suit of armor is surely tedious, and would only be used in the most dangerous areas. But hey, at least you don't need to invent appropriate protection from scratch, right?


First off, awesome setting.

Second, as the poster above said, primitive fishing implements, scaled up for human size. And realistically, boats. If there's enough land that humans evolved, surely there's some floaty jank that they can at least make a raft out of.

As for underwater combat, I think spearfishing poles (polespears?) are pretty cool.

Also, if you're talking deeeeeeeeeeep underwater (over 2m), then there is very little light penetration and camoflauge, ambushes, etc. come into play due to the low visibility. Goggles would be an amazing invention, or perhaps, clear eyelids like frogs or something that allow people to see clearly underwater. In my opinion, this sounds like just one culture of people whose came from ancestors from a much larger land mass, so they wouldn't have necessarily evolved special adaptations to this environment.

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    $\begingroup$ You're not a skin diver, are you? I've been down 40+ feet (12 m) in a freshwater lake, and there wasn't enough light attenuation for my eyes to notice (the human eye is comfortable down to about 1/100 of summer daylight, at least, with no loss of acuity). In the ocean, you have to get about 20+ m deep before light becomes a problem, not 2 m. $\endgroup$
    – Zeiss Ikon
    Feb 6, 2020 at 15:00
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    $\begingroup$ k then listen to this guy. I'm a land mammal and I googled light attenuation and got a graph that looked like its 1% incident light at 2m and didnt know if that's a lot or not. $\endgroup$
    – doe
    Feb 6, 2020 at 15:18
  • $\begingroup$ 1% is about the difference between summer sun and office lighting -- but that seems not to be reasonably clear water, because it strongly disagrees with my experience. britannica.com/science/seawater/Optical-properties gives 150 m as 1% light in the clearest ocean... $\endgroup$
    – Zeiss Ikon
    Feb 6, 2020 at 15:53
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    $\begingroup$ @doe when you say "2m" do you mean "two metres" or "two miles"? I suspect that may be where the confusion is arising... $\endgroup$ Feb 6, 2020 at 16:06
  • $\begingroup$ Serious light attenuation kicks in from 200metres, with the twilight zone to 1000metres, below that it's dark. $\endgroup$
    – Separatrix
    Feb 7, 2020 at 8:14

I think it would be fun to see the humans make use of ocean bio-weapons.

Examples might be cultivating poisonous sea anemones to grow on the end of long poles, so you could stab at approaching sharks with them. Or having sharp toothed eels encased in long glass tubes, where only their mouth reaches out to bite your foes. Shell producing creatures with sticky bases could be attached to vulnerable human parts for armor.

And my favorite, just as we train hunting dogs, they could train hunting dolphins (or whatever the alien equivalent is) in a cooperative relationship.


Melee combat is not the right tool. Your people would be at disadvantage in that and nobody reasonable picks a fight in which they are at disadvantage.

1. nets

Farming is done in shallow waters where enough light still reaches to the bottom. So the height you need to protect is not that big and you can put protective nets around them. That will keep your workers safe from predators and the ‘crops’ from large herbivores.

If the nets are breached, the workers get out. They are not trained to fight, they need to direct their effort towards other skills, so they don't try it. Net-builders bring in new nets and hunters deal with predators if any got in.

You said fibrous materials are readily available, so this should be worth it.

2. shepherd dogs

In the deeper waters the main thing you can do is herding fish. So recruit a suitable marine equivalent of shepherd dogs. Probably something like dolphins.

And you always want to have a ship around. A ship with sails and oars is faster than swimming, stays afloat even if all the crew is dead tired and can have some harpoon guns mounted.

3. hunting/defense ships

Since you are able to build ship-mounted harpoon guns (the weapon is not immersed, so all the usual mechanisms—bow, torsion springs (ballista) and trebuchets—all work), use them against the larger threats. Any activity when there is a risk of attack by a kraken or a large shark should be guarded by a ship with harpoon guns.

Use them in sufficiently large fleets that when kraken tries to attack one ship, the others can fire at it and kill it before it manages to do too much damage.

The bottoms need to be protected so a kraken can't bite through them with its beak. Either using a layer harder than that beak, perhaps from glass or some ceramics, or by spikes and blades so the kraken would cut itself if it tried to attack there.

Alternatively some mechanism for extending spikes when a kraken attacks could work.

4. encumbering harpoons

The old techniques for hunting whales involved having air balloons attached to them. Those would prevent the whale from submerging and create drag, both of which would help tiring it to exhaustion. You can use that too, or in some cases, you might want to try the opposite, having weights or anchors at the end of the ropes so when you throw or shoot the harpoon at something dangerous, you can get away and it will not be able to follow, because it will be dragging the anchor.

5. apropos torsion springs

With a torsion spring and a pulley you should be able to create a mechanism that would at least somewhat work as a harpoon gun underwater. Better than nothing.

6. escape mechanism

When going down to fight some predator with the hand harpoon or simple harpoon gun, you can have a rope connecting you to the ship with some mechanism that can pull you out of the water quick. A weight and some pulleys or another torsion spring should do.

That way you can wait for the predator to get close, take a shot at it and get out quickly in case you miss or if the predator does not die immediately (piercing weapons are even worse than cutting ones in this aspect) and can still swim faster than you.

7. keeping watch and planning

You don't defend from random attacks. You make sure they don't happen, or that you know about the predator ahead of time and prepare for the fight. So standing watch is important. On watch towers on the shore, on ships, and sending out scout dolphins (or whatever ‘dog’ you domesticated).


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