Believe it or not, Churchill cooked up a plan to specially modify a couple fo battleships to give them extra Armour (to survive air attack) adn sail them intot he Baltic sea to attack German shipping. The admiralty were of course flabergasted with this idea and managed to move it onto the back burner. I don't know if the idea of it being impossible to enter the Baltic is correct, but if the Germans have enough airpower (and use it) it should be a one way ticket.