[andrewmunsell]

Oh yes, I am (though I am absolutely not a real engineer nor do I have any experience with subs) just questioning why they would need to bolt it from the outside anyways. If it was to keep occupants in, I would imagine that a door that opens outwards would solve that issue if submerged, and would still be openable on the surface

[rightbyte]

It is a simpler design to screw the nuts from the outside. Otherwise the hull would need through hull screws attached to the door or some sort of clamp around the hull edge by the door opening.

[rsaxvc]

Guess: weight and cost savings