Thank goodness for watertight integrity! I assume, unlike surface ships, all WT doors and hatches on subs are secured at all times.
I have great appreciation and fascination for the men who serve on subs. One of the most horrific ways of dying I can imagine is to be on an imploding submarine, deep beneath the surface...at night!
I doubt if any would really realize what hit them should/when that happens; the pressure/water shock would be so sudden and the sea would be merciful.
Under the sea, it's always night.
God bless our sailors...