Hey Ducimus,
First of all thanks for the mod.
Not sure if this is an error or intended to be this way, but last night and this morning I took a Porpoise down past 445ft (basically as deep as I could go using the gauge) and sustained no damage or flooding. I did it once in the torpedo training mission and again in a new campaign.
It's a fresh install only with TMO 2.5
I'm going to read through the docs now to see if there's any mention or reason for this.