Atlantis

As I said on Wednesday, there are two ways you can get underwater in fantasy.  You can find a technological method or introduce a magical version.  Both are viable with having been used in the genre before.  There are two things to consider though:

1. Availability–  If the technology or magic doesn’t exist to go underwater then you can’t use it.  This is truer for tech than magic because you can have ancient relics found for the latter.  Still, you can’t have a submarine appear in a story where it’s been Bronze Age tech the whole time.  Even if this stuff does exist, your heroes need to have access in some fashion.  They can’t just be given this stuff or abruptly have it for no reason other than to move the plot along.
2. Dependency–  Are either of these choices dependent enough for the heroes to want to use them?  For example, you’re shown a submarine and a water-breathing ring.  The former is uncomfortable and has no defenses, which may turn adventurers towards the magical item.  Yet, the ring has a tendency to lose its charge after two hours.  You can’t depend on being near the surface when that time is up.  Now, the submarine seems more sensible.

Probably more to think about, but they’re situational.  Availability covers the big part as far as I’m concerned.  So, what are the pros and cons of each category?

Magical Gear

Pros–  These tend to be enchanted items, which means they’re small and don’t add to the discomfort of moving around.  Magical gear requires less knowledge on the heroes parts because they’re put on and activated either immediately or by a word.  Fewer working parts makes sense for adventurers who wouldn’t normally be experienced in using advanced machines.  Less of a chance of breaking too since enchanted items are known to be difficult to damage.

Cons–  Unlike technology, it can be fairly easy to lose a magical item.  Rings can slip off fingers or the hand be bitten off by a shark.  This is why clothes tend to be safer, but even those can be at risk.  I know I said there’s less of a chance of breaking, but it’s possible and adventurers have less of a chance of fixing magical gear than technology.  There’s the threat of the magic being nullified as well.  This can be done by an enemy, a startled creature, or just passing through a non-magic zone.  One could say that the higher risk of something going wrong comes with the easier use.

Technology

Pros– This category is typically a type of submarine or a scuba suit.  It’s usually the former, which means the heroes are kept together.  We’ll keep talking about submarines because they have the greatest amount of pros.  They’re armored, which protects from the elements and aggressive animals.  It allows for communication instead of signing and hoping it isn’t too dark for allies to see.  Weapons can be placed on these devices, which helps preserve the adventurers’ supplies.  Maps can be stored and checked without having to worry about water damaging the paper.  Finally, a basic submarine can make a faster escape than a person who is swimming.

Cons–  The downside here is entirely due to the complication of the tech.  Your average adventurer won’t know how to steer, read the gauges, or do real repairs.  They may learn basics quickly, but a major emergency means they’re in trouble.  You can say this is remedied by them hiring a captain with experience, but that’s a non-combatant that has to be protected.  That person dies and it could be all over.  Submarines and scuba gear are also bulky, so they can’t get into areas that a person using a ring of water breathing can get into.  Finally, a submarine can be broken so badly that it will sink along with everyone inside.  If it’s already deep then there’s no way to get out and swim to the surface before you drown.

What to do?

That’s really up to you.  An author decides on how effective these things are going to be since they’re telling the story.  If you don’t want the magical gear to be negated then don’t do it.  If the submarine doesn’t break then that’s your choice.  Consider that the pros and cons would be thought of by the people in the fantasy world too.  They may very well work towards countering those issues.  So, think about how far along the magic or tech would be in general.  I would assume a few early accidents would get some of the major bugs out of the advancements.

Also, you can always combine them.  Adventurers can take a submarine, but have magical gear for when they have to leave for investigating.  There’s no rule that says it really has to be one or the other.  Kind of makes this ‘versus’ post rather silly now that I think about it for a second.  Oops.