Actually, I myself, DO NOT INTEND to play the RC submarine in icy water. I DON'T EVEN ICE-FISH although I do see ice-fishermen on and off at the local river .
I present this question scenario on the basis that if I can learn from the best, the most extreme, I can apply it with ease to run my sub in the fall weather of slightly chilly water.
That is why I did not post that CRAZY British video right away.
Who on earth would launch a RC sub in freezing cold weather if you can launch your sub in an indoor heated swimming pool instead ???