Nautical campaigns, or even underwater adventures, are kind of a niche thing in Dungeons & Dragons 5e.
Officially, there’s the excellent Ghosts of Saltmarsh campaign book, which casts a wide net through a shoal of delightfully spooky aquatic adventures from the earliest days of D&D, including evocative titles like the Sinister Secrets of Saltmarsh and The Final Enemy.
Otherwise, however, there’s not a whole lot of meat on this particular fish bone.
That’s kind of a shame, because some of the explicitly underwater-themed items found in the Dungeon Master’s Guide are among the most fun found anywhere in the game.
Chief among them is the Mariner’s Armor, a great magic item that should be compulsory for any underwater adventurer worth their salt.
Source: Dungeon Master’s Guide
This magical armor is decorated with motifs of fish and shells. While wearing Mariner’s Armor, you gain a swimming speed equal to your walking speed. Also, if you ever start your turn underwater with 0 hit points, the armor causes you to rise 60 feet towards the surface.
This is some of my favorite item design in the whole game because it not only provides a consistent, tangible mechanical benefit, but also a really fun, unique effect that makes the Mariner’s Armor come alive.
During the age of sail, it was relatively uncommon for sailors to know how to swim. A powerful navy with access to magical crafting abilities might approach that same problem by crafting sets of Mariner’s Armor to give drowning sailors a second chance if they go overboard.
Sea Elf commandos, armed with knives made from megalodon teeth might wear them on nighttime raids against the dreaded Sahuagin. A wizard’s apprentice might don their battered suit of Mariner’s Armor to go searching for rare spell components amid a shark-infested reef at their master’s command.
Because Mariner’s Armor is a type of armor design, rather than a specific set (similar to a +1 magic weapon) and can be based on the following armor types, it’s an incredibly versatile magic item that can be applied to just about any character class.
|Padded||Medium||11 + Dex modifier||—||Disadvantage|
|Leather||Medium||11 + Dex modifier||—||—|
|Studded Leather||Medium||12 + Dex modifier||—||—|
|Hide||Medium||12 + Dex modifier (max 2)||—||—|
|Chain Shirt||Medium||13 + Dex modifier (max 2)||—||—|
|Scale Mail||Medium||14 + Dex modifier (max 2)||—||Disadvantage|
|Breastplate||Medium||14 + Dex modifier (max 2)||—||—|
|Half Plate||Medium||15 + Dex modifier (max 2)||—||Disadvantage|
|Chain Mail||Heavy||16||Strength 13||Disadvantage|
If you’re a dungeon master looking to give one (or more) of your players a suit of Mariner’s Armor, there are virtually no limitations on the character classes that can make use of a set – with the exception of the monk and barbarian.
Mechanically, having your swimming speed increased to your walking speed is a huge bonus.
Swimming (as well as climbing and crawling) costs 1 extra foot of movement, effectively halving your speed. Being able to move your walking speed (especially if you’re playing a character that has above average movement speed, like a Tabaxi, for example) underwater is a massive advantage.
This is especially important because the dangerous things you encounter underwater, from the Reef Shark to the Water Naga, are all going to be able to move at close to twice your swimming speed.
Given the fact that characters can hold their breath for a length of time equal to 1 + their Constitution modifier (30 seconds is the minimum), being able to move further and accomplish more while submerged can be the difference between survival and a watery grave.
The survival component of the Mariner’s Armor – which will send you rocketing towards the surface if you drop to 0 hit points – can be a literal lifesaver if you begin to drown beneath the surface.
Where can I get Mariner’s Armor?
The cost of buying a suit of Mariner’s Armor obviously varies depending on the price of the armor type on which it’s based. Padded Armor costs as little as 5 gold pieces, and a full suit of Plate will run you an eye-watering 1,500 gp before you’ve even imbued it with any magical effects.
In our Magic Items Pricing Guide, we can see that the cost of a common magic item can range from 50-100 gp, and that a rare magic item can be worth as much as 5,000 gp.
Mariner’s Armor is uncommon, and so sits somewhere between the two. I think that, in a “standard” magic item shop, a fairly straightforward way of pricing Mariner’s Armor (per the pricing rules for magic items in the Dungeon Master’s Guide) is to take the base cost of the armor and add 500 gp.
However, this is a game about simulating real life, so taking the concept of supply and demand into account is also important.
A suit of Mariner’s Plate in a magic item shop located in the capital of a great empire, where there’s a wizard’s college, dwarven forges, and enchanted gear is more common, might therefore fetch the 2,000 gp that our little base cost + 500 gp rule suggests.
In a frontier town beside the ocean, where an evil Sahuagin priest is causing sea levels to rise and storms to better the coast, you could expect to shell out that same 2,000 gp for Mariner’s Padded Armor.
Conversely, a society of aquatic elves might just leave their suits of Mariner’s Scale Mail lying around, and happily outfit some helpful, polite adventurers with their own sets for free.
In terms of places you might find a suit of Mariner’s Armor, any seafaring race of sentient creatures might have one lying around. There might be a suit of Mariner’s Leather Armor on a pirate ship, donned by whichever crew member whose job it is to swim under the enemy vessel and disable the rudder.
An order of paladins sworn to guard the shores against an encroaching race of monstrous kaiju (definitely aboleths and their giant squid servants) might have a set of Mariner’s Plate going spare from the last time they lost a brother on an away mission.
The local pearl divers might all wear Mariner’s Studded Leather for an extra dash of speed – not to mention the peace of mind that, if things go south beneath the waves.
If you’re a dungeon master looking to run a seafaring campaign, putting a suit or two of Mariner’s Armor in your game can be a great way to give your players a decidedly on-theme advantage when they venture beneath the surface of the deep blue sea.