They say saving while submerged is not a good idea, however I have never had a problem.
Im afraid if the save is corrupted is your screwed, your only hope is to fall back to a previous save. That is why I save early and save often. I probably save at least 6 to 8 times a patrol session and that does not include the in base saves. I keep 4 save slots and over right them in order.
As to the TC not being able to go past 4x it was probably because you were close to or on the bottom. Its sort of a safety feature to keep you from slamming into the bottom by accident. That dammed 'D' key can be leathal.
