Within Barotrauma, players violate the Geneva Conventions quite a lot. To an extent that it rivals the sheer heresy that Rimworld players act out within their games. However, I have noticed a lack of a specific armament that would greatly effect player vs. player combat.
What I propose is a shell that delivers a chemical payload from a railgun. Imagine loading up a canister with mustard gas or cyanide and launching it at an enemy vessel. Imagine being within said vessel and you watch in horror as a titanium mass tears through your hull and, upon contact with the interior, it delivers its chemical payload, dumping it into your air.
Its a horrifying aspect but it would be one that should be utilized within our beloved depths of Europa. The damage should also scale with a medic with the plague doctor perk, to help balance it of course.