Has this been entertained already?
I think being underwater should protect you from gun fire that’s shot into the water, if not 100%, at least partially.
Canon fire would still be deadly if hit under the water.
While underwater, guns should be unusable, or have a high drop off rate if they can be used. Then we have a perfect opportunity to introduce a speargun. It could be used for offense, or hunting/fishing as part of a future update.
I just think having some differences to account for between above and below water combat would add to the strategy, and coordination of crews
