I have been trying to remember this movie since I could remember.  I was a kid when I saw it with my dad (early early 1990’s).  I think I remember a group of people stuck in a submarine or a vessel of some sort.  The part I remember is when a lady opens up a small hatch and starts crawling through it.  She begins to sweat and panic and I believe halfway through her venture into the tunnel water rushes in and she ends up dying