I was thinking the same thing too, after your comment.
It depends on if the bridge clamshells / sail access is to a free flooding area, or if the area he is climbing into is actually dry, and closed off from sea by the hatch.
If it is dry, this tells me that the vaunted Iranian submarine pictured above doesnt have much of a dive depth.
regards
Judicial Meanz ( bubblehead)
I just can't remember where....