Mitchaa - I can't think of a situation when they wouldn't wear their immersion suits, especially at night.
As Satsuma has said , they had a version (I don't know which one) of STASS (Short Term Air Supply System) and will have trained using it in the dunker.
Dclbydaplha - so it is S-AIS
The original concept of AIS was a LOS collision avoidance IIRC.