Why would modern humans not use scuba gear for missions underwater? (But freedive instead)

Question

I am writing the lore for a currently in-development open-world freediving adventure game and am stuck with trying to keep some things scientifically founded. Overall the game style is closer to realistic than to stylized or cartoony (it's a 2.5D game to make this feasible in a small studio) and the lore should fit this atmosphere.

The Setting

The time period would be a couple of decades into the future. Mankind has made universal progress, including some artificial, biological enhancements to themselves, but with 10 billion people they do not keep the oceans clean by any means. Warming and souring of the ocean has also drastically influenced its food chains.

Base of the game lore is a number of similar species of sirens coming out of hiding from the depths of the ocean as that got further polluted by humans. While not willing to communicate with anyone at the surface, they seek to reclaim the sea and forbid humans from traversing across the surface, let alone diving deep.

The Sirens abilities/technology

They are a sapient species with a generally inferior level of technology and possibly magic (albeit in terms of magic I'm mainly thinking of body-enhancing "natural" compounds which the player can later use as well).

Their main perk is agility and eyesight/echolocation underwater, making even just rapier-style cutting weapons rather efficient. Using the thousands of water mines humans have deployed over the decades as well as natural resources, they can craft sufficient explosives or corrosives to sink ships and submarines especially after learning of weak points.

Furthermore sea life is clearly on their side (or they breed and train it), allowing them to deploy areas of fish and jellies for alarm/scouts + passive defense and sharks as deadly guards (not as offensive attackers since RL sharks already suffer enough under their reputation as bloodthirsty killers :( ).

The Lore vs Gameplay Problem

Yet with that background of not making the Sirens absolutely overpowered, organized teams of Navy Seals or similar equipped with scuba/rebreathers would have easy game defending themselves and counter attack at least in the Epipelagic Zone (above 200m). Specially designed agile submarines with omnidirectional defense capability (instead of just stealth like today) could go even deeper.

What I am aiming for the game though is that less organized and peaceful freedivers (biologically enhanced to be mostly proof against diver sickness and pressure) are the ones who will manage to discover secrets regarding where the sirens come from, what they truly want and eventually lead to some form of resolution. The gameplay shall be in the direction of Subnautica: Always having to take your air into account and you are able to make air pockets with slow air-generators to secure progress.

Best solution to achieve this would be to make any form of high pressurized air supply (as gear or in submarines) mostly unusable. How to explain that without taking the game fully into magic territory is my problem.

It always irked me in Subnautica why you don't have proper scuba tanks. Sure the "on board" compressor on your suit might be technologically limited, but you'd still bring a regular tank at very least for emergencies which can be refilled at a full size compressor at a base.

I'd like a more proper solution with potential for gameplay elements (like providing POIs).

My Thoughts/Ideas

One thing that crossed my mind would be the sirens possessing a type of crystals or technology that emits a radiation which mainly affects pressurized oxygen, similar to how supposedly microwaves only heat up water. But turns out that on its own, is a myth - it's not how household microwaves actually work.

Further notes

• The land dwellers do need to send humans when they see the situation as a war (which they will, because transporting goods across the sea is as important as today). The issue of wireless transmission being very limited underwater has not been solved, making drones easy targets due to their cable and AI has not progressed further enough to truly replace humans for underwater missions (small AI drones will be partners for the protagonist though).

• It does not necessarily need to be an absolute exclusion of scuba gear for everyone. The freedivers will just have a higher chance to not immediately incite aggression by the Sirens as at least some (probably one of the species) will recognize that humans who dedicate themselves enough to dive without gear do actually care about the well-being of the ocean and could be friends like dolphins are.

• I am okay with toning down human ingenuity. Like surely one could probably think of drone-swarms that maintain a short-range network via ultrasound to be controlled from the surface without cables and if pressured O2 is really the weakpoint of scuba gear, there are chemical and electrical ways of generating O2. The game isn't at all about military tech however.

Yet I would like to prevent the player from getting the obvious feeling "all this would be so much easier with scuba tanks and some spear guns; no human would risk doing this freediving".

Am happy about any suggestions! Huge thanks!

Answer 1

There are a number of qualities that make free diving preferable over scuba for tasks that can be accomplished in the small number of minutes a free diver can remain submerged.

First, free diving is, well, free. There were still places at least into the 1970s where free divers harvested pearls in water up to 30 meters or deeper, without fins or full-face masks, using simple stones for ballast (the rock drags you down, you let go when you're ready to go back up) and eyes-only goggles with pressure compensating squeeze bulbs attached (to prevent the goggle pushing into the eye socket), plus nose clips so breath need not be wasted to prevent water invasion.

Given a free diver can train to stay down for more than five minutes, and using ballast can descend more than fifty meters in a minute and still have time to work and surface, diving with either snorkle, mask, and fins or even without that much assistance is very practical for tasks that can be divided into time segments and for which the same workers will stay on the job for years at a time.

Additionally, free diving has fewer hazards related to pressure than SCUBA -- one need not exhale continuously during ascent, is at far less risk for decompression effects and will not encounter oxygen toxicity or nitrogen narcosis. And the limited equipment used (if any) is inexpensive compared to tanks, regulators, and high pressure compressors or paying for tank fills.

Answer 2

Stealth

Man-made materials like metals, plastics, and ceramics have very distinct qualities that allows Sirens to immediately identify submarines and scuba gear from miles away. It's so distinct if you were to try to use subs or scuba gear, you would immediately be swarmed by thousands, or maybe even millions of Sirens and thier aquatic allies. However, a human is made up of more or less the same stuff as sea-lions and dolphins; so, unless they get really close to a free diver, they can't actually tell that they are dealing with a human. This lets free divers pass mostly undetected through the water attracting no more than the occasional curious observer.

Also, if getting out to sea is important, perhaps these free divers could use small wooden boats like canoes so that they just look like driftwood.

Answer 3

There are several major issues with deep diving: narcosis, acute oxygen toxicity and decompression sickness. The specific details of each aren't necessarily important here, only to note that they are all caused by breathing high pressure air. Diving mammals don't actually need to breathe high pressure air... indeed, the deepest diving mammals breathe out before going down, to allow their air spaces to collapse flat. This subject has been covered in more detail elsewhere (here's one of my answers to Are Air-Breathing Merfolk Viable? to get you started).

Your bioengineered free divers can do long deep dives thanks to various blood and muscle modifications, and are much less vulnerable to various problems that people diving with scuba gear or rebreathers would be (but not necessarily immune... see taravana and the many kinds of freediver blackout, etc).

Best solution to achieve this would be to make any form of high pressurized air supply (as gear or in submarines) mostly unusable

Submarines don't actually use high pressure air, because that's a hazardous environment for humans and technology. They have very sturdy pressure hulls that can keep the water out and maintain regular air pressure in the habitation sections. Remotely operated or autonomous underwater vehicles neededn't have any air in them at all. You'll need a different excuse for those, unfortunately. You'll also have to think of a reason why depth charging a hostile underwater intelligence (up to and including the use of nuclear weapons) is not considered.

This might be as simple as highly effective weapons built using electroceptive animals, perhaps as suicide attackers, that are attuned to the strong fields of electric motors, but not mere muscles and nervous systems so as to avoid attacking sea life by accident?

Answer 4

Anti-tech organisms:

Your Sirens have evolved organisms to combat humans - not human organisms, but the technology they possess. Plastic-eating bacteria thrives in the polluted ocean, and any plastics or rubber rapidly degrade. Metal-sniffing explosive sharks patrol the waters, ready to ram any ship or human artifact. Planktonic jellyfish have been been evolved to adhere to glass, metals, and plastics, rapidly blinding anyone with a mask. Then the jellyfish send a chemical signal to attract predators and other things made to degrade human tech.

The sirens quite rightly assume that humans are hamstrung without their precious gadgets, but weren't counting on humans actually improving their species. So they haven't developed things that directly attack humans. They must rely on good old-fashioned weapons to kill denuded humans, instead.

Answer 5

Divers can perceive like the fishes through the skin

It is dark deep down and often a little bit of silt raised by the stormy sea can drastically reduce the visibility even close to the surface.

The divers through the skin can feel the small vibrations in the water. They can perceive anything even small fishes approaching without looking in that direction or seeing it through the muddle. The drawback is that they have to abandon the safety of the wetsuit. But actually by abandoning the wetsuit they also gain some agility.

The bubbles disguise their position

The bubbles coming out of the regulator are noisy. Not only they reveal the position of the diver, but they also identify them as a stranger. The rebreather that does not leave a bubble trail behind is not fit for deep dives because it would not be possible to regulate the internal pressure, or at least you would need a compressor that would suck out exhaled air and store it in another pressure tank.

Storing oxygen in the muscles is better

As others pointed out when you rely only on the oxygen transported by the blood when you dive has some problems. When the pressure increases and nitrogen and carbon dioxide dissolve better in the blood a lot of new dangers appear, like narcosis or decompression sickness. Storing oxygen in the muscles like other deep diving mammals do is way better.

Answer 6

The sirens are hopeless against real organized action. Various types of underwater munitions can be designed that destroy and debilitate them, nuclear submarines will completely overpower any resistance. Consider how much money and effort countries spend to keep marine life from dying. They can wipe the sirens out easily, especially in shallow places where free diving is an option.

The sirens must be a small enough threat that nobody with real equipment wants to bother dealing with them. There are several ways to expand this space:

• SCUBA is highly regulated. Why don't modern humans buy a lot of guns to defend themselves, take steroids to be stronger and take amphetamines to be smarter? The government doesn't like it. Just say that in your world, some stupid moral panic has led to a situation where only the very-wealthy or well-connected are able to acquire SCUBA gear, and everyone else is stuck diving. Or perhaps there is a sea war going on between human powers and all SCUBA is reserved for use by the military.
• The targets are poor. Full SCUBA gear is expensive, and there's a lot of costly maintenance you need to do. It's not as bad as, say, owning a plane. But it's prohibitive for a working class person, especially in developing countries.
• Conflict with sirens is over-regulated or illegal. Therefore ordinary people don't want to deal with the lawsuit that follows. People who are already criminals with no standing in society don't care, as they have little to lose. Perhaps they are actually poachers. These people cannot afford or are not permitted to acquire SCUBA gear. Or being caught with SCUBA gear would incriminate them.
• Because of sirens, demand for SCUBA gear is high in wealthy countries and they cost a lot more than in our world. This is more convincing as a temporary thing, as eventually you would expect supply to catch up and drive prices down.
• The sirens are ancestral enemies and for religious or cultural reasons, the divers consider it dishonorable to not face them unaided. Maybe there are even laws preventing "unsportsmanlike" methods of fighting them. This is a situation similar to hunting in many places, where you need a license, training and only some methods are permitted. People do it for sport, not out of necessity.
• The sirens are irrational. They use some kind of weapon that specifically targets SCUBA. They fail to display the same ingenuity in developing weapons against freedivers (because that would make them overpowered). I dunno, maybe a magic fish that goes and cuts the SCUBA hose, but for some reason it just won't slice the carotid artery. Maybe a giant magnet that pulls all the SCUBA tank in (although the player would wonder why they don't make polymer tanks). Or maybe they're a degraded civilization that no longer remembers how to make future-tech artifacts, and their ancestors so happened to leave them only anti-SCUBA devices and nothing anti-freediver (or anti-nuclear sub).
• The sirens live in some kind of narrow cave complex with tunnels just wide enough for a siren to squeeze through, and sirens are similar size to humans. Thus a human with a SCUBA tank cannot fit into many of these tunnels. Note that you have to be careful here because you could just tow the tank behind you - so you should combine this with one of the other options (eg. divers are too poor to buy the less common towable tank). This does go with the idea of exploiting air pockets.

Also, since when does Subnautica not have SCUBA tanks? Obviously they are more advanced given that it's a far-future world with colony starships, and I assume decompression sickness is omitted to keep gameplay simple, but https://subnautica.fandom.com/wiki/Ultra_High_Capacity_Tank_(Subnautica) sure looks like a SCUBA tank to me.

Answer 7

You could just make the freedivers too poor to acquire the diving equipment that exists. Though you would need some way to how they became biologically enhanced without being able to pay for it. This could be perhaps be explained away as simply being hereditary once applied so they could be enhanced due to the circumstances of their birth without ever having paid for it.

Answer 8

Perhaps it could simply chase them away:

• Scuba gear makes humans look like monsters, so the sirens wont go near anyone wearing it. You'll never even see them.

• The military have secretly been attacking the sirens for years, so the Sirens hide from anyone wearing it.

• The sound (or bubbles) of scuba gear is frightening because it disrupts the Sirens echolocation.

None of this completely removes subs/scuba divers, so the gameplay may have to rotate around a group of people who learn to co-operate with the Sirens, and take on the techno-industrial empire/military etc... Kinda cliche, and not quite what you had planned, but it means your enemies near the end can be the human military!

Or perhaps these ideas means that a special ops team operating without scuba gear can be much more sneaky and successful that regular frogmen...