I have seen a number of posts on this site about the difficulties of technological advancements for those who dwell beneath the surface of the sea, and this is colouring my treatment of mer-people in my story.

My mer-people look like a human with a cetacean-like tail in place of their legs. They can breathe both air and water. When breathing water, they take in water through the nose and mouth, and eject water through gill slits on the sides of the chest, between the ribs. When breathing air, they close their gill slits and breathe in the manner of land-dwelling mammals. Merfolk are capable of altering their buoyancy in water. They do not spend more than a few hours out of water at a time, and must use their arms to move effectively on land.

I have been considered what sort of body armour might be made by people whose only access to metal might be via occasional trade with surface dwellers, and whose native technology is neolithic, and whose warfare is similarly primitive.

The first type of armour I have considered would be made from the bones of sea mammals such as whales, as well as whale baleen, fashioned into plates and joined together with natural fibers.

The second type is similar to the first, save that it would be made from abalone shell, which is known for its impact resistance, and could be polished as an artistic statement, as well as being protective.

These would both be varieties of lamellar armour.

How feasible would these types of armour be? Please consider factors such as the ease of manufacture of each type and effectiveness against primitive weapons such as spears and knives, as well as the natural weapons of large, dangerous, aggressive sea creatures such as sharks?

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    $\begingroup$ "How effective might each type of armour be?" Against what weapons? Looking at the natural world, most weapons used by marine animals either stab or are sound weapons. I don't think any type of armour would stop sound weapons. $\endgroup$ Jul 14, 2022 at 13:30
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    $\begingroup$ Related, possible duplicate, but not necessarily. They even come-up with the idea of blubber as armour. $\endgroup$ Jul 14, 2022 at 13:35
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    $\begingroup$ In case your merpeople go out to the surface, do they completely leave water so that they crawl on their lower body like say a naga? If yes, they should develop scales on the tail, and these scales could be fashioned into armor for body (or plain grow on upper side as well). $\endgroup$
    – Vesper
    Jul 14, 2022 at 13:35
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    $\begingroup$ @sphennings, I've cut down the number of questions. $\endgroup$
    – Monty Wild
    Jul 14, 2022 at 14:00
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    $\begingroup$ @Vesper, whaleskin doesn't make good leather. Age of sail whalers used to tan the only good bit of skin on a whale for use as overalls: a blue whale's penis skin. $\endgroup$
    – Monty Wild
    Jul 14, 2022 at 14:31

2 Answers 2


Firstly, you should probably forget about trying to protect yourself from large predators like sharks using armor. Things live in the sea that can eat crabs and turtles and have the jaws and dentition to back it up; you're not going to be able to cobble together good enough armor to defend yourself against those sorts of things, and anything with small enough teeth that you can easily ward it off with bits of stone and shell and plant is not going to be much of a threat to you in the first place.

Secondly, you only really have to worry about two kinds of weapons... pointy polearms, and small knives. Swinging swords and axes underwater is pointless and futile, and projectile weapons are both hard to make and even when you can make them they'll be pitifully short ranged. Knives are used at close range when you can actually grapple with your opponent, and finding the gaps in primitive armor to stick a blade through is probably not going to be very challenging.

Thirdly, everyone always gets too hung up on armor, and forgets about shields. They're much easier to make and pretty effective against a whole range of attacks in a way that primitive armor can't ever be. They also don't need to be nearly as protective as armor, as having someone stick a spear through your shield is less bad than having someone stick a spear through your chest, for example.

Fourthly, combat between tail-using swimmers is going to be a bit different to combat between bipedal walkers. There's a much smaller cross-section of your opponent exposed to you... either head/shoulders if they're coming towards you, or the tail if they're moving away from you.

Lastly, stuff rots fast in the sea. By definition, it is always wet, and readily accessible to any microbe or planktonic scavenger that floats past. Shell and stone will last well, but everything else has a strictly limited lifespan. Armor seems likely to be designed to be made quickly and easily, and repaired or replaced easily and often. Complex and timeconsuming things (stitched leather, for example) would be expensive luxuries because they are consumables in a way that similar items on dry land are not.

So, I posit:

  • Shields. Making a stiff shield might be awkward, but bone and shell might be enough to provide a framework to build upon with some other softer but tougher material... skins or plants. A big turtle shell might be nice, but I can see problems with species being hunted to extinction in the event of protracted warfare.
  • Helmets, and possibly pauldrons. Bone and shell again, probably woven together with plants or sinews and onto a harness. Much smaller than shields, so easier to engineer. Smooth and curved as possible to to help keep the wearer streamlined and to help deflect spear/trident tips.

Everything else is probably of increasingly limited usefulness other than looking nice or signifying wealth, if you live in a society where doing such a thing is possible and useful. Your merpeeps are unlikely to be engaging in huge pitched battles (difficult to think of a parallel to an agrarian bronze age for a strictly underwater civilization), but much more likely to be doing raiding for livestock, slaves or plain old theft of shiny stuff. Raiders move fast and light. Slowing yourself down just makes attacking and defending in that sort of environment far harder than it needs to be.

  • $\begingroup$ Isn't a shield going to suffer the same issues as a sword? Even trying to move it edge-on you are still moving a fair amount of mass, and if you aren't exactly edge-on it's going to be increasingly difficult. $\endgroup$ Jul 16, 2022 at 21:11
  • $\begingroup$ @SoronelHaetir you aren't trying to chop bits of people off with it, though. Lateral movement is the main thing you need for defense, and that's the direction of least resistance. I'm not sure what "fair bit of mass" means here, because it needn't be heavy nor is mass quite so important underwater (and real world shields can't be that heavy either, if you think about how they need to be used). A curved surface with a few carefully cut vent slots should work well enough. $\endgroup$ Jul 17, 2022 at 8:24

Not Great

It is hard to imagine how whale bones or shells could be fashioned into plates around the body. Seashells are brittle and bones are either flexible when alive or brittle when dead. The shape of a bone is also not suited to making plates.

I suggest the standard armor is a gambeson made of matted kelp. A gambeson is armor made by taking the duvet off your bed and wrapping it around your body.

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You might cut through the gambeson with a good sword swing. But you will not cut through the gambeson and chop off the arm underneath. It is even harder if you try sawing back and forth with the sword. Side-note mermaids do a lot of sawing since they cannot swing their swords fast underwater.

Mermaids wear something similar except instead of layers of cotton or linen they use layers of kelp.

The standard armor is made of kelp. But the fancy armor is made of copper. This is either bought or forged by the mermaids on their island forges. Copper is softer than iron but it is good because it does not corrode underwater.

Only a disgustingly wealthy mermaid wears iron armor. Iron armor is disposable armor underwater.

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    $\begingroup$ Isn't fiber armor very susceptible to thrusting attacks? I would expect spear/trident type weapons to be common underwater rather than either slashing or sawing. $\endgroup$ Jul 14, 2022 at 18:35
  • $\begingroup$ @SoronelHaetir All I can tell you is the gambeson was the most common medieval armor and the spear was the most common weapon. $\endgroup$
    – Daron
    Jul 14, 2022 at 19:10
  • $\begingroup$ I was thinking more lamellar armour. $\endgroup$
    – Monty Wild
    Jul 14, 2022 at 22:09
  • $\begingroup$ I'd rather go for pressurized kelp, add other fibers if any available, like mentioned baleen which could also work as an extra protective outside layer. However there are questions regarding mermaids themselves, whether they can sustain high water pressure required to compress kelp into something that won't break while swimming, whether there is glue available to make kelp into semi-solid structure, etc. $\endgroup$
    – Vesper
    Jul 15, 2022 at 9:00
  • $\begingroup$ @Vesper The kelp would be woven into a mat rather than pressurised. $\endgroup$
    – Daron
    Jul 15, 2022 at 9:36

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