I have a society of merpeople that have developed sonar in order to hunt, gather resources, and in some instances communicate. They use organically created weaponry (sharpened coral, animal incisor daggers, turtle shell shields, etc.) and live in woven seaweed fortresses. A rift has been created, and the society has split, leaving two groups of merpeople about to head into war over the organic and natural resources (Prime seaweed for building, excellent coral flexibility in this area, the water currents funnel the fish juuuust right, etc.). I was thinking on how to beef up those defenses, when I hit a block. My merpeople live ~150 meters down, and although they can utilize photosynthesis, it is not a necessity to them. Most of their structures are either built in as part of a kelp forest, or spread out into a hut city of sorts. There is a stigma about caves in their world being cursed by the god of water, so holing up (in some cases literally), is out of the question. They have the ability to burrow, but mining through stone is only done for the rich and the powerful due to its difficulty, and so is not commonly done. Digging is easily done provided the ground is soft enough for a coral shovel to penetrate.

If they have sonar, then there would never be a surprise attack that would gain the advantage on the enemy, and directional warfare would probably be akin to space warfare, in that an attack could come from any direction.

My flaw was in first thinking about the defenses, but I couldn't come up with a reason to not create essentially a bubble of seaweed or shells (think the part in 300 where they have the shield turtle), and just go on with their daily lives using sonar to say, "Oh hey, the enemy is over there".

My question is thus: How would warfare be conducted in an underwater environment? Is there a way to gain the upper hand at the start of a battle?

I'm looking for something like an attack of some sort (blitzkrieg, sneak attack, etc.), but intelligence, espionage, and sabotage might work as well, provided the actual reason for the wars (resources) would remain usable.

  • $\begingroup$ Related, but not duplicate: worldbuilding.stackexchange.com/questions/17484/… $\endgroup$
    – Anoplexian
    Jun 20, 2016 at 15:21
  • $\begingroup$ Does each side have individuals constantly monitoring (sonaring?) the surroundings? Because it seems like if not, that could be an advantage for the attacking side to take advantage of. $\endgroup$
    – user
    Jun 20, 2016 at 15:28
  • $\begingroup$ @MichaelKjörling I mean even if I did or didn't have sonar, I'd still have guards looking out, so presumably yes and it would just make patrol(?) duty easier. This is assuming they would patrol at all, and not just post sentry posts with constant sonar. It'd kind of depend on how war is conducted in general. If the sonar is seen as widespread and common, I feel like warfare in general would avoid anything that would be detected like that, but hence the question, as I don't really see how it would be conducted otherwise. I may just have a narrow outlook on warfare though. A tactician I am not. $\endgroup$
    – Anoplexian
    Jun 20, 2016 at 15:28
  • $\begingroup$ I think one thing you should consider for "lookouts" is how far beneath the surface do they live? It gets dark pretty quickly as you descend into water. At even just a few tens of meters, water is quite opaque, and a lot of the time, merfolk are depicted as living deeper than that. Disney's Ariel movies are not really an accurate depiction of the amount of ambient light at depth. $\endgroup$
    – user
    Jun 20, 2016 at 15:33
  • 1
    $\begingroup$ I'm pretty sure there's a stigma about caves, not a stigmata. That would be ... bloody. $\endgroup$
    – David K
    Jun 20, 2016 at 19:43

3 Answers 3


While sonar is better at penetrating water than light is, it doesn't give the user a perfect picture of their environment. If the surrounding area has trees, reefs, or coral, those will all make it difficult to detect a passing enemy using sonar in the same way that hills or forests can stop people from seeing approaching enemies in our air-based environments. Even without dense kelp forests, the sort of long sea grasses that are common in areas like the Mediterranean Sea would effectively obscure merfolk crawling through them close to the sea floor. Even schools of fish or pods of whales could be used as cover from sonar, effectively forming moving shields blocking sonar from imaging what's behind them.

Alternately, blocking sonar is as simple as stopping sound waves from reflecting off of you. Armor made of soft-bodied creatures like sponges or something similar might be sufficient to hide the wearer from someone searching for them with sonar, or at least diminish the reflected sound wave to the point where it sounds like something much smaller than a merfolk.

  • 2
    $\begingroup$ And Sonar can be fooled. I imagine fish and other critters come close to the fortresses and what-not. Why not drive these animals towards your enemy to overwhelm or confuse their sonar, or imitate their sonar signatures in some way. "Oh, look, the whales are coming again....wait....that's no whale!" $\endgroup$ Jun 20, 2016 at 19:26

Don't trick the technology, trick the user

Sonar like all forms of wave detection is open to interpretation by the operator. Case in point, modern submarines and stealth craft do not completely mask their signature, but reduce it to the point where the signature appears to be something innocuous. Given your merpeople don't have stealth technology, they could use an opposite technique. Instead of trying to appear as a fish, they can build some larger movable cover and appear as a whale or a squid, that way a squad of MerSoldiers, appears as a single large entity instead of many man-sized entities, leading to unskilled sentries to dismiss it.

Bad Communication Kills

The United States had detected the Japanese Naval Air Squadrons plenty of miles out before Pearl Harbor. Why then did the US not respond? Communication mix-ups from higher sources indicated that an American Bomber wing was due to arrive, but said bomber wing was delayed. Only when the fighters got into visual range did everyone realize their goof up. Subterfuge can still work in this situation if you don't want to use the previous idea. Some false missives, a killed off messenger, and you have a massacre on your hands.


I can think of a few methods that circumvent sonar sentries or are general of use in warfare.

  • Underwater drums or trumpets for distraction.
  • Herd innocent fish to block accurate sonar images.
  • Bait and lure sharks to confuse. Any aggressive and/or poisonous fish would do.
  • Tame a whale to use as underwater 'elephant'.
  • Dolphin squads for light cavalry.
  • Orca squads with nets for heavy cavalry.
  • Sneak along the ocean floor and attack key targets from behind.

Inspiration can be found from generals like Alexander the Great, Caesar, Lu Tzu, Napoleon, and often underwater versions can be envisioned.

Confusion to the enemy!


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