My idea is that you equip yourself so that nobody wants to attempt to go weapon on weapon on the ship. It's about deterrence.
The best deterrence in the north would be an undersea-capable submarine, and hopefully a nuclear submarine that could stay there. If a submarine is there and it's known, nobody will come forward. There we achieve deterrence because the cost inflicted would be too high to come and have bullets of ice breakers against bullets of ice breakers.