Concrete is not very water proof on its own. It's also quite hard to prevent cracks from forming, even with reinforcement.
There is a lot you could do, like neoprene barriers on the skin of the fuselage, sacrificial anodes, spray sealant on the poured concrete. But at that point, you might as well not even have the fuselage and just build a regular, ol' concrete bunker.
alt Hacker News
Concrete is not very water proof on its own. It's also quite hard to prevent cracks from forming, even with reinforcement.
There is a lot you could do, like neoprene barriers on the skin of the fuselage, sacrificial anodes, spray sealant on the poured concrete. But at that point, you might as well not even have the fuselage and just build a regular, ol' concrete bunker.