russian missiles launched from 50 meters will get through ice upto 2 meters thick i have no clue how they do it but i think its to do with the gas they use to eject the missile
also the typhoon is so large that the ice you saw riding on your deck would probly only be about 1/4 the way down the hull on a phoon
the phoons hatches are very strong and can break ice the sail is designed for under ice in the first place it cuts it first then cracks the rest of the ice around it and thus making it easier to open hatch and fire theres a video on it some where when i can find it
read my under ice guide that will give you a good idea too its on the subguru downloads page