Thanks Keith. I guess another way to know if you were under ice, in poor visibility, would be by temperature?

I guess I was wondering how feasible it would be to make some removals/mods to the conning tower and generally top surfaces of the boat. to make it a little more sustainable when surfacing through new ice say a foot thick. A bowhead whale can do 18" but yes no protuberances. Just aiming for a little credibility in my book which finds a type 1X boat in arctic waters and with some difficulties operating in ice while on a mission . Also I presume torpedo doors (outer) could be welded shut and a bit of steel plating added to the nose to give it a little more ice protection. Some limited damage to the boat upon surfacing through the ice would be become part of the story but again need the credibility.
Would the type 1VX milch cow boats have had some limited welding capability and other retrofit capability for on the spot work, beyond their basic refueling role?

Regards,
Larry