[@Eyeris] Vaughtar, once awake, isn't stone anymore. He's bone, flesh and blood. His bones 'only' are inhumanly massive and dense and he has grown an abundance of muscles with similar properties. I guess without actively working against it he would indeed be completely unable to float and consequently be in deep trouble since he needs air just like everyone else does.

So, yes, he might have a very vital interest in this u-boat remaining dry on the inside, even though he hasn't yet fully grasped the idea of what a submarine actually is. And even if it weren't for that glass pane very close to shattering in front of him, he possible wouldn't just look away while a completely mad Hirsch tries to rip Zesiro apart.

The question is... How to work out this fight ?