In my case, REALLY cold! 1963 - 1972 in a submarine (SSBN and SSN) with two Extended trips to the Arctic seas, occasionally under ice. Ice in the bilges, cold sleeping on mattress on the torpedo room deck (tank top). Sometimes terrifyingly anxious moments, other times mostly slow and quiet. Glad I did the tour, but wouldn't want to repeat it. Other runs in the Med trailing "bogies" and occasionally finding undersea mountains that were not on the charts, yet.
Memorable was a repair job I did on a radio aboard USS Nautilus in New London.
Smooth sailing and following seas!