Underwater Combat (5e Variant Rule)
Underwater Combat[edit]
The standard 5e rules for underwater activity and combat seem to lack the tension and flavor that adventures in this environment deserve. I developed these homebrew rules from various sources, google searches on holding your breath, a bit of math, and playtesting. These rules should give a great roleplaying experience for almost all water situations, such as traversing underwater tunnel, fight with creature trying to drag you under, falling into the water while in armor, etc.
Doing Stuff Underwater[edit]
Movement[edit]
Unless you have a swim speed, swimming is treated like difficult terrain effectively halving movement. Your underwater swimming speed is the same as your surface swimming speed. Your armor and encumbrance will have an uncontrolled affect on your swim speed and direction. In addition to the intended, spent, movement that the character does, the character will also move straight down at 5 feet per round if holding the equivalent of light armor, 15 feet per round if holding the equivalent of medium armor, or 25 feet per round if holding the equivalent of heavy armor. A Strength (Athletics) check with a DC equal to the character’s AC (without magic bonuses, but with disadvantage if any worn armor gives the wearer disadvantage on Dexterity (Stealth) checks) will halve this sinking movement. This will likely require the character to spend some, if not all, their movement to counter the downward sinking movement, or speed their descent if this is their desired movement direction.
Combat[edit]
Melee attacks are made at disadvantage underwater, unless using a dagger, javelin, spear, or trident.
Ranged attacks are made at disadvantage underwater, unless throwing any of the weapons listed in melee attacks above or while using a weapon with the loading or reload properties. Ranged weapons cannot go past their “normal” range bracket.
Armor[edit]
If you are in water with your armor, likely you will want to take it off. The don/doff table for PHB 146 lists doff time (converted to rounds). This could be halved if you have assistance. You can attempt to remove your armor in the water, but you may not use your move during this time and it counts as doing your action (using up “breath” if submerged). If you have something sharp, you may attempt to cut your armor off with a successful DC 15 Dexterity (Acrobatics) check to cut the doff time in half.
| Category | Don | Doff |
|---|---|---|
| Light Armor | 10 rounds | 10 rounds |
| Medium Armor | 50 rounds | 10 rounds |
| Heavy Armor | 100 rounds | 50 rounds |
| Clothes | 5 rounds | 5 rounds |
| Backpack | 1 round | 1 round |
| Shield | 1 action | 1 action |
Equipment[edit]
Firearms. Most renaissance firearms are unable to be fired underwater. If a renaissance firearm is submerged, it is rendered unusable for 10 minutes until it dries and must be reloaded with new powder before it can be used again.
Holding Your Breath[edit]
Each character has a number of rounds of “breath” equal to 5 × Constitution score + 20. If you spend 10 consecutive rounds breathing deeply (as your action), you may add 10 rounds of breath.
While underwater, certain activities will expend extra rounds of “breath” from your reserve:
- Taking an action expends ½ round of “breath”
- Doing a move to swim expends ½ round of “breath”
- Moving at 5 feet swim rate expends no extra rounds of “breath”
- If you take damage while underwater, you must make a DC 10 Constitution saving throw or lose 1 round of “breath”
Once you run out of “breath”, you must make a Constitution saving throw vs:
DC = 10 + #rounds out of breath + damage taken/10 + 1/move + 1/action Fail: lose ½ total max hit points (or one failed death save if already below 0 hit points) and disadvantage on the next saving throw you make against running out of breath (due to taking in water)
It takes an action to take a breath, which restores 5 rounds of “breath”
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